Internal services

CHAPTER 8.1
This chapter gives guidance on meeting the
Technical Requirements forinternal
services, including:
the supply of hot and cold water
„„
plumbing
„„
gas
„„
electrical installations.
„„

8.1.1 Compliance 01
8.1.2 Provision of information 01
8.1.3 Water services and supply 01
8.1.4 Cold water storage 03
8.1.5 Hot water service 04
8.1.6 Soil and waste systems 05
8.1.7 Electrical services and installations 06
8.1.8 Gas service installations 07
8.1.9 Meters 07
8.1.10 Space heating systems 08
8.1.11 Installation 08
8.1.12 Extract ducts 10
8.1.13 Testing and commissioning 11
 2020
Internal services
1 1
CHAPTER 8.1

8.1.1 Compliance Also see: Chapter 2.1

Internal services shall comply with the Technical Requirements and take account of service entries, ground
hazards and chemical attack.
Internal services which comply with the guidance in this chapter will generally be acceptable.
Adequate precautions against ground hazards and the entry of gas i.e. radon or gas, from landfill sites, should be provided
as necessary. Further guidance can be found in BRE Report 211 ‘Radon: guidance on protective measures for new dwellings’,
and BRE Report 212 ‘ Construction of new buildings on gas-contaminated land’.

8.1.2 Provision of information

Designs and specifications shall be produced in a clearly understandable format, include all relevant
information and be distributed to the appropriate personnel.
Clear and fully detailed drawings should be available on site to enable work to be carried out in accordance with the design.
Designs should be issued to site supervisors, relevant specialist subcontractors and suppliers, and include the following
information:
Location of sanitary fittings.
„„ Central heating pipe runs.
„„
Drainage runs.
„„ Underfloor heating pipe runs.
„„
Location and size of water storage cisterns and cylinders.
„„ Gas supply pipe runs.
„„
Hot and cold water pipe runs.
„„ Electrical outlets, switches and consumer units.
„„

8.1.3 Water services and supply Also see: water regulations and guides, BS EN 806
Water services shall be based on the pressures and flow rates supplied from the incoming main.
Components shall be selected and installed to ensure satisfactory service for the life of the system,
with suitable precautions taken against corrosion and damage. Issues to be taken into account include:
a) suitability of materials and components c) durability
b) adequate supply d) protection from the cold.

Suitability of materials and components

Relevant standards for materials and components used in domestic water systems include:
BS EN 806 ‘Specifications for installations inside buildings conveying water for human consumption’.
BS EN 12897 ‘Water supply. Specification for indirectly heated unvented (closed) storage water heaters’.
BS EN 1057 ‘Copper and copper alloys. Seamless, round copper tubes for water and gas in sanitary and heating applications’.
BS 1566 ‘Copper indirect cylinders for domestic purposes’.
BS 3198 ‘Specification for copper hot water storage combination units for domestic purpose’.
BS 7291 ‘Thermoplastics pipe and fitting systems for hot and cold water for domestic purposes and heating installations in
buildings’.
BS 8558 ‘Guide to the design, installation, testing and maintenance of services supplying water for domestic use within
buildings and their curtilages. Complementary guidance to BS EN 806’.
8.1
 2020
Internal services
22
CHAPTER 8.1

Adequate supply
The design and installation of the water services supply should:
be in accordance with building regulations, statutory
„„ ensure that stop valves within the curtilage and outside the
„„
requirements and the recommendations of the water supplier home are protected by a shaft or box
ensure drinking water is provided at the kitchen sink direct
„„ ensure service pipes are a minimum of 750mm below the
„„
from the supply pipe or, where this is impracticable, from a ground surface – where this is not possible, adequate
storage cistern containing an adequate supply of precautions should be taken against frost and
drinking water mechanical damage
be based on a minimum 1.5 bar dynamic pressure at the
„„ ensure that underground ducts are sealed at both ends to
„„
stop valve inside the home prevent the entry of fluids, vermin and insects
ensure a minimum 20L/min flow rate is available at the stop
„„ be of materials which are safe and minimise the risk
„„
valve inside the home of corrosion
account for pressure and flow rate reductions (a wider
„„ be in accordance with the recommendations of the water
„„
supply pipe may be required inside the home) supplier, including compatibility of the supply with the
account for pressure fluctuations and surges, which may
„„ materials and fittings.
occur within the system and potentially damage fittings
(surge arresters may be required)
The water system should be capable of being drained (hot and cold services separately).

Durability
The hot and cold water service should be installed using corrosion resistant pipes and fittings.
In areas where pitting corrosion of copper cylinders occurs, it may be necessary to fit aluminium protector rods. These should be
fitted during manufacture in accordance with the relevant British Standard. Sacrificial anodes should be installed where required
by the water supplier.

Protection from the cold

To reduce the risk of freezing, water services should be located in the warm envelope of the home. Where they are located in
unheated spaces, they should be insulated and not affected by cold. Insulation should be provided:
around water services, including pipework (in accordance
„„ as specified in the design (but not beneath a cold water tank)
„„
with Tables 1 and 2), cisterns and vent pipes on each side of raised tanks in unheated roof spaces
„„
(particular care is needed around bends and junctions, in accordance with BS 6700 or BS EN 806 and BS 8558.
„„
especially near openings to the outside air, such as eaves)

insulation
thickness

insulated
water pipes

cold air

Table 1: Minimum insulation thickness to delay freezing inside domestic premises for cold water systems
8.1

Outside pipe Minimum insulation thickness (mm)

diameter (mm) Thermal conductivity of material at 0°C W/(mK)
0.025 0.030 0.035 0.040
15 30 45 70 91
22-28 12 15 19 24

The conditions assumed for the table are:

air temperature -6°C
„„ ice formation 50%.
„„
water temperature +7°C
„„
 2020
Internal services
33
CHAPTER 8.1

Table 2: Examples of insulating materials:

Thermal conductivity W/(mK) Material
Less than 0.020 Rigid phenolic foam.
0.020-0.025 Polyisocyanurate foam and rigid polyurethane foam.
0.025-0.030 PVC foam.
0.030-0.035 Expanded polystyrene, extruded polystyrene, cross-linked polyethlene foam, expanded nitrile
rubber and improved polyethylene foam.
0.035-0.040 Standard polyethylene foam, expanded synthetic rubber and cellular glass.

Where the floor is of suspended construction, the underfloor ventilated void

to suspended floor
water service should be insulated as it passes through the
ground and the ventilated space.

min.
750mm

any distance

8.1.4 Cold water storage

Cold water service shall be provided in accordance with statutory requirements and be adequate.
Cold water storage should be provided with suitable capacity and include primary feed cisterns where indirect water heating
systems are installed. Cold water storage should be provided:
to supply an open vented hot water storage system
„„ to supply cold water outlets (where not connected to the
„„
(where required by the water supplier) mains supply).
Cisterns should:
be accessible for inspection and maintenance
„„ have holes neatly formed with a cutter in the positions
„„
be protected by a rigid close-fitting cover (non-airtight) that
„„ shown in the design
also excludes light and insects be suitably supported.
„„
BS 6700 provides the following recommendations:
Storage capacity for small homes – only cold water
„„ Storage capacity for small homes
„„
fittings – 100-150L. – supplying hot and cold outlets – 200-300L.
Storage capacity for larger homes – 100L per bedroom.
„„
Warning and overflow pipes:
should be provided at each cold water cistern, to a suitable
„„ should be situated 25mm from the shut-off water level in the
„„
external discharge, unless permitted by water regulations cistern
where it may be internal if it is conspicuous may dip below the water level in accordance with water
„„
8.1

should be adequately sized (19mm minimum)

„„ regulations, terminate vertically downwards or be fitted with
a horizontal tee where it discharges.
The cistern bottom should be continuously supported by materials such as:
softwood boarding
„„ oriented strand board type OSB3 to BS EN 300, laid with
„„
marine plywood
„„ the stronger axis (as marked on board) at right angles to
chipboard type P5 to BS EN 312
„„ the bearers.
 2020
Internal services
44
CHAPTER 8.1

Access should:
be provided to the main roof space and voids that contain
„„ include a minimum 1m2 platform located for
„„
cisterns and tanks, etc. (not required to roof spaces maintenance purposes
containing only water pipes) include securely fixed boarded walkways between the
„„
be via an opening (access hatch) with a minimum width of
„„ opening and the cistern or other permanent equipment
520mm in each direction (boarding should be securely fixed without compressing
not be located directly over stairs or in other
„„ the insulation).
hazardous locations

8.1.5 Hot water service Also see: BS 8558

Hot water service shall be provided in accordance with statutory requirements and be adequate for the
demand and consumption.
Hot water services should be designed in accordance with Tables 3, 4 and 5, and:
the minimum flow rate should be in accordance with the
„„ have the design flow rate available at each outlet when the
„„
statutory requirements and generally be available; it may total demand does not exceed 0.3L/s (where simultaneous
be less where the pressure and flow rate of the incoming discharge occurs, the flow rate at individual outlets should
supply falls below 1.5 bar not be less than the minimum rate).
Table 3: Flow rate and temperature requirements
Outlet Design flow rate (1) Minimum flow rate (2) Supply temperature °C (3)
L/sec (L/min) L/sec (L/min)
Bath (from storage) 0.30 (18) 0.15 (9) 48
Bath (from combi) 0.20 (12) 0.15 (9) 40
Shower (non-electric) 0.20 (12) 0.10 (6) 40
Wash basin 0.15 (9) 0.10 (6) 40
Sink 0.20 (12) 0.10 (6) 55
Notes
1 The design flow rate should be used to establish the hot and cold pipe sizes to provide the flow rate quoted at each outlet when that outlet is used on its own.
2 The minimum flow rate should be available at each fitting when that fitting is used simultaneously with one or more other fitting(s) as shown in Table 4.
3 The supply temperature is the temperature at the outlet. In accordance with BS 8558 the water temperature at an outlet or thermostatic mixing valve should be at
least 50°C within 1 minute of running the water.

Table 4: Hot water demand and simultaneous use

Bathroom Shower room Hot water demand (5)
Bath only Bath + Shower (1) 1st Shower room 2nd Shower room L/sec (L/min)
 (2) 0.20 (12)
 (3) 0.15 (9)
  0.25 (15)
   0.35 (21)
 (2) 0.20 (12)
8.1

 (4)
 0.20 (12)
 (4)
  0.30 (18)
  0.20 (12)
Notes
1 Shower may be over the bath or in a separate enclosure within the bathroom.
2 Demand based on ‘Design’ flow rate of bath.
3 Demand based on minimum acceptable boiler output.
4 Demand based on use of the shower in preference to the bath.
5 The hot water system should supply at least the hot water demand stated and take account of distribution heat losses through the pipework. The suitability of
instantaneous systems (combination boilers) will be limited by their performance as quoted by the boiler manufacturer.

Hot water storage should comply with the minimum capacity in Table 5 (based on a draw-off temperature of 60°C), and where
appliances require greater volumes, the capacity should be increased accordingly.
 2020
Internal services
55
CHAPTER 8.1

Table 5: Minimum storage requirements

Shower only Bath only Bath and shower(s)(1) Two baths
60L 120L 145L 180L
Note
1 Maximum of two showers (excludes instantaneous electric showers).

Where systems are heated by off-peak electricity, the storage capacity should be in accordance with the recommendations of the
electricity supplier.
Where homes have one bathroom or shower room, the system should be able to provide adequate hot water:
immediately after the bath has been filled, for tasks such
„„ for a second bath after 20 minutes.
„„
as washing
Where homes have two or more bathrooms, the system should be able to provide adequate hot water immediately after each of
the baths have been filled, for tasks such as washing.
Where a shower is installed, adequate provision should be made to ensure that the outlet temperature of the water is not
significantly affected by the use of other hot or cold outlets in the home. This may be achieved by the provision of a thermostatic
shower mixing valve, the appropriate design of pipe sizes or dedicated supplies.
Instantaneous systems (using combination boilers) produce hot water on demand (generally at lower flow rates than
storage systems), and should only be used where:
simultaneous demand for hot water is limited. Where there
„„ storage combination boilers have the capacity as required
„„
are three or more outlets, the design for simultaneous in Table 5. Where boilers can control and prioritise hot water
discharge can omit the outlet at the kitchen sink outputs the storage capacities can be less than the figures
in Table 4 subject to manufacturer’s recommendations on
meeting the demand.
Storage systems provide higher flow rates than instantaneous systems, and:
require a suitable space for the siting of the storage vessel
„„ where vented, should be provided with an expansion pipe.
„„
Unvented hot water storage systems should be:
assessed in accordance with Technical Requirement R3, or
„„ installed by competent installers.
„„
meet the requirements of BS EN 12897 and be the subject
of third-party certification, e.g. Kitemarking (applies to both
the assembled system and components)
Hot water cylinders should be:
„„supported in accordance with accessible for maintenance
„„
manufacturer’s recommendations insulated as specified in the design.
„„
„„installed vertically, unless designed otherwise
Where an immersion heater is fitted, it should be:
appropriate for the type of water supplied to the home
„„ located to facilitate replacement
„„
controlled by a thermostat
„„ fitted with an on/off switch.
„„

8.1.6 Soil and waste systems Also see: BS EN 752 and BS EN 12056
8.1

Soil and waste systems shall be in accordance with relevant building regulations and installed to ensure
that effluent is removed without affecting health or creating unnecessary noise and smell.
Soil and waste systems should be:
in accordance with the requirements of the water supplier
„„ 900mm
min.
adequately ventilated at the head of underground drains
„„
(this may be by a soil pipe or separate ventilation pipe)
openings soil pipe or
adequately ventilated at each branch
„„ ventilation
pipe
arranged to ensure foul air from the drainage system cannot
„„ less than 3m
enter homes (e.g. ventilated to 900mm above openings when
within 3m)
fixed neatly and securely to provide the correct falls
„„
fitted to prevent the entry of vermin.
„„
 2020
Internal services
66
CHAPTER 8.1

Air admittance valves should:

be used to allow air to enter the drainage system (but do not
„„ have free movement of air around them which can be
„„
avoid the need to ventilate it adequately) achieved by ventilation grilles, discreet gaps around the
where used to terminate a soil pipe, comply with
„„ boxing or ventilation of the boxing into a ventilated roof void
BS EN 12380 or be assessed in accordance with (the ventilation area should be 2500mm2 minimum unless
Technical Requirement R3 otherwise specified by the manufacturer)
not be positioned in areas which are liable to freezing
„„ where positioned within the home, be accessible
„„
for maintenance.
Sound insulation should be provided to soil pipes passing
through homes by:
timber framing
an encased boxing, using a minimum 15kg/m2 board
„„
material and wrapping the pipe with a minimum 25mm of line the enclosure or
wrapthe pipe with 25mm
unfaced mineral fibre (the insulation should be continued unfaced mineral fibre
through the thickness of each sound-insulating floor).
the material of the enclosure
should have a mass of
15 kg/m2

Sanitary fittings should be:

installed with accessories, such as chains and plugs
„„ fitted without using excessive packing
„„
secured using non-ferrous or stainless steel screws or
„„ fitted to ensure WC lids and seats are stable when open.
„„
fixings appropriate to the weight of item being secured

Waste disposal units should be:

provided with adequate support
„„ connected to the drainage system in accordance with the
„„
fitted with a tubular trap (not bottle or resealing)
„„ manufacturer’s instructions.

The junctions of wall tiling with baths and showers should be made watertight using a flexible sealant to accommodate
movement. The manufacturer’s instructions should be followed.

8.1.7 Electrical services and installations Also see: BRE report ‘Thermal insulation: avoiding risks’
Electrical installations shall be provided in accordance with relevant regulations, codes and standards.
The installation shall ensure safe and satisfactory operation and be protected from chemical attack.
Electrical services and installations should:
comply with BS 7671 ‘Requirements for
„„ be installed in accordance with the
„„
electrical installations’ manufacturer’s recommendations
comply with BS 6004 ‘Electric cables. PVC insulated and
„„ ensure cables are not placed under, against or within
„„
PVC sheathed cables for voltages up to and including thermal insulation, unless they have been appropriately
300/500 V, for electric power and lighting’. sized and derated
have fittings and components located in accordance with
„„ ensure PVC covered cables are not in contact with
„„
relevant building regulations polystyrene insulation.

Rooms should be provided with the minimum number of 13A outlets listed in Table 6 (dual outlets count as two).
Table 6: Minimum number of outlets
8.1

Room Outlets Notes

Kitchen/utility 8 Where homes have separate areas, the kitchen should have a minimum of four outlets and the
utility room four. Where appliances are provided, a minimum of three outlets should be free for
general use.
Living or family room 8 A minimum of two outlets near the TV aerial outlet.
Bedrooms 6 (4) A minimum of six outlets for the main bedroom and a minimum of four outlets for other bed-
rooms.
Dining room 4
Landing 2
Hall 2
 2020
Internal services
77
CHAPTER 8.1

Cables without special protection, such as an earthed vertically or horizontally in shaded zone
to switch or outlet 150mm wide
metal conduit, should be positioned:
„„vertically or horizontally from the outlet or switch being served
„„within the shaded zone in the diagram, or
„„a minimum of 50mm from the surface of a wall, or a minimum
of 50mm from the top or bottom of a timber joist, or batten in
a floor or ceiling.
Where the position of switches or sockets can be determined
from the reverse side of the wall or partition, the zone on one
side of the wall or partition applies to the reverse side.
Lighting outlets
Lighting outlets should be provided:
in each room, hall, landing and staircases
„„ in the common areas of homes and controlled by either
„„
with two-way switching at each floor level in a staircase
„„ manual switching or automatic light-sensitive controls.

Cooking spaces
Cooking spaces should:
have a minimum 30A supply which is suitably switched
„„ where provided, have cooker panels located to the side of
„„
and terminated the cooker space.
have a 13A socket outlet where there is a gas supply
„„
Electrical supply to gas appliances
Where a gas appliance requires an electrical supply, a suitable fixed spur or socket outlet should be provided.

TV
Aerials are not required; however, one of the following should be provided:
a concealed, coaxial cable from the roof void to a terminal
„„ a conduit and draw wire or suitable alternative.
„„
outlet in the main living room

8.1.8 Gas service installations Also see: Chapters 6.2, 6.8, BS 6400 and BS 6891
Gas service installations shall be adequate and comply with the gas safety regulations, and be in
accordance with relevant standards and codes to ensure safe and satisfactory operation.
Gas service installations should ensure:
service pipework up to and including the emergency control
„„ where there is a gas supply to the home, a gas point at
„„
valve and meter is in accordance with the requirements of the cooker space should be provided. This is not required
the gas transporter, gas supplier and primary meter owner where an electric hob is provided
installation of pipework and appliances complies with
„„ where gas pipework is to be installed in timber frame,
„„
relevant standards and codes including those published by allowance is made for differential movement.
the Institution of Gas Engineers and Managers (IGEM) or
Gas Safe Register (GSR)

8.1.9 Meters Also see: Chapter 6.1

8.1

Openings in walls for meter cabinets shall be structurally adequate and prevent dampness entering the home.
Openings set into external walls should be provided with: cavity tray

DPCs and cavity trays

„„
lintels (except for purpose-designed built-in meter boxes).
„„
Meters and associated equipment should be located to be
reasonably accessible and not subject to damage.
Domestic meters may be of the following type:
Built-in (to the outer leaf of the wall).
„„
Surface-mounted (on an external wall).
„„
Semi-concealed (sunk into the ground adjacent to the
„„
outer wall).
meter box
Individually purpose-made compartments in accordance
„„
with the recommendations of BS 6400.
 2020
Internal services
88
CHAPTER 8.1

8.1.10 Space heating systems Also see: Chapter 6.8

Where space heating is provided, it shall be in accordance with the relevant codes and standards, and
ensure safe operation.
Where appropriate, space heating systems should comply with the following:
BS 5410 ‘Code of practice for oil firing’.
BS EN 14336 Heating systems in buildings. Installation and commissioning of water based heating
systems.
BS 8303 ‘Installation of domestic heating and cooking appliances burning solid mineral fuels’.
BS EN 12828 ‘Heating systems in buildings. Design for water-based heating systems’.
BSRIA guide BG 4/2011 ‘Underfloor heating and cooling’.

Space heating appliances, including all components and controls, should be of a type approved by the relevant authority,
including:
Solid fuel – Solid Fuel Association, Heating Equipment
„„ Electricity – British Electrotechnical Approvals Board
„„
Testing & Approval Scheme Oil – OFTEC.
„„
The provision of whole home or central heating is discretionary. Where provided, it should be designed in accordance with
Table 7, recognised standards, and:
the number of air changes per hour from kitchens and
„„ design temperatures should be verified by calculations and
„„
bathrooms should account for any mechanical ventilation not by performance tests
where rooms contain open flued appliances, the rate of
„„ the main living room should have a heating appliance or a
„„
air change used for the design should be increased in heat output as part of a whole home heating system
accordance with BS EN 12828 temperature calculations should be based on
„„
a -3°C external temperature.
Table 7: Room temperatures and ventilation rates
Room Room temperature °C Ventilation rate (air changes per hour)
Living room 21 1.5
Dining room 21 1.5
Bedroom 18 1
Hall and landing 18 1.5
Kitchen 18 2
Bathroom 22 2
Toilet 18 2

8.1.11 Installation
Internal services shall not adversely affect the stability of the home and be installed to ensure
satisfactory operation. Issues to be taken into account include:
a) fitting of pipes and cables c) concealed services.
b) notching and drilling of joists
8.1

Fitting of pipes and cables

Services should:
comply with Chapter 5.1 ‘Substructure and ground-bearing
„„ not be located in the cavity of an external wall, except for
„„
floors’ where they pass through the substructure electricity meter tails
be protected by a sleeve, or ducted, when passing through
„„ not be buried in screeds unless permitted by relevant codes
„„
structural elements and not solidly embedded of practice.
Where copper pipes are permitted in floor screeds, they should be:
sleeved or wrapped so that they can move freely along the
„„ jointed with capillary joints.
„„
length and at joints and bends
Pipes should:
be adequately secured with suitable clips or brackets
„„ have adequate falls (where appropriate)
„„
be installed neatly with clips spaced to prevent sagging,
„„ be installed with adequate room for thermal expansion and
„„
but not restrict thermal movement contraction to avoid damage and noise.
 2020
Internal services
99
CHAPTER 8.1

Metallic tape should be placed behind plastic pipework, where it is concealed behind wall surfaces, and would otherwise not be
located by a metal detector or similar equipment.
Joints in pipes should be made:
strictly in accordance with the manufacturer’s instructions
„„ using lead-free flux recommended by the pipe manufacturer,
„„
with traces removed immediately after jointing.

Fire stopping should be provided around any services which penetrate fire-resisting floors, walls or partitions. Where a proprietary
system, such as an intumescent seal is used, it should be installed in accordance with the manufacturer’s instructions.

Notching and drilling of joists

Notching, drilling and chasing to accommodate service pipes and cables should either:
comply with the clauses below, or
„„ be designed by an engineer.
„„
Solid timber and studs
Table 8: Limits for notching and drilling solid timber members
Location Maximum size
Notching joists up to 250mm in depth Top edge 0.1-0.2 x span 0.15 x depth of joist
Drilling joists up to 250mm in depth Centre line 0.25-0.4 x span 0.25 x depth of joist
Drilling studs Centre line 0.25-0.4 x height 0.25 x depth of stud

holes separated
by a min. 3 x
hole diameter

100mm min. holes located on the centre line in a

between notches zone (0.25-0.4 x span) from the end
and holes and max. diameter = 0.25 x joist depth
notches located in a zone
(0.1-0.2 x span) from the end and
max. notch depth = 0.15 x joist depth

Where the structural strength is impaired by notching or drilling, the element should be replaced or correctly repaired.
Holes should be spaced at a minimum of three times the hole diameter.
Notches and holes in the same joist should be separated by a minimum horizontal distance of 100mm.
Instructions should be obtained from the designer when notching and drilling, where:
the joist is deeper than 250mm, or
„„ it is close to heavy loads, such as those from partitions,
„„
the dimensions are not in accordance with Table 8, or
„„ cisterns, cylinders and stair trimming.

I-joists
Preformed holes are provided, and additional holes and notches should not be cut without the approval of the manufacturer.
Metal web joists
Services should run in the gaps between the metal webs. Conduits may need to be inserted before the joists are fixed in position.
8.1

Lightweight steel
Light weight steel should be used in accordance with Chapter 6.10 ‘Light steel framed walls and floors’.

Concealed services
Services concealed in walls or floors should be located so that significant cracking of the surface does not occur. Where chases
in walls are necessary, their depth should not exceed:
1/6 thickness of the single leaf for horizontal chases
„„ 1/3 thickness for vertical chases.
„„
Hollow blocks should not be chased unless specifically permitted by the manufacturer.
 2020
Internal services
10
10
CHAPTER 8.1

Pipes under floor screeds should:

min. 25mm cover
be protected by wrapping or ducting
„„
have adequate allowance for thermal expansion,
„„ insulated pipe
particularly at changes of direction. within screed

Screed cover should be a minimum of 25mm over pipes and

insulating material, and:
where pipes cross, it may be necessary to form a duct to
„„ for in-situ suspended concrete floors, the location and depth
„„
achieve adequate cover of pipes should be approved by the designer.

8.1.12 Extract ducts Also see: Chapter 8.3

Ductwork to intermittent and continuously running mechanical extract ventilation systems shall ensure
satisfactory performance and durability. Issues to be taken into account include:
a) building integration d) installation
b) resistance to airflow e) terminals.
c) control of condensation

Building integration
The route of ductwork should take account of other building elements. Ductwork passing through structural elements should not
adversely affect the structural or fire performance of the building. Where alterations to structural elements, such as I-joists,
are required, this should only be carried out in accordance with the manufacturer’s recommendations, or be designed by an
engineer in accordance with Technical Requirement R5.
The fire requirements of the building should be in accordance with relevant building regulations and standards. Issues that
should be taken into account include:
„„suitable detailing of components passing through other „„ the integrity of protected stairs and halls
elements of the building „„ the integrity of walls and floors.
„„the location and type of dampers and firestops to be used

Resistance to airflow
Ductwork systems should be designed to minimise the resistance to airflow, and be formed from compatible components.
Rigid duct is preferable to flexible, but where flexible duct is used, it should be restricted in length to ensure that the airflow
resistance does not prevent the designed ventilation rate from being achieved. Flexible duct should be installed:
straight
„„ in accordance with the manufacturer’s recommendations.
„„
Bends should generally be formed with proprietary rigid components. Where flexible duct is used to form bends on an
intermittent extract system, they should be restricted to a maximum of:
„„ two for systems up to 30 L/s „„ one for extract rates higher than 30 L/s.

Control of condensation
Where extract ductwork passes through unheated spaces, it should be continuously insulated to achieve a thermal resistance
equivalent to a minimum of 25mm of insulating material with a thermal conductivity of 0.04W/(mK). This can be achieved by
using:
suitable pre-insulated ductwork, or
„„ a proprietary insulation system.
„„
8.1

Alternatively, the ductwork can be fitted with a condensate trap that discharges to the outside or installing the duct to slope to
the outside.
unheated
unheated space
space

pipe to drain duct sloping to

condensate to eaves the outside

condensate trap
 2020
Internal services
11 11
CHAPTER 8.1

Installation
Ductwork should be installed in a neat and workmanlike manner, be securely fixed, and have:
adequate support throughout its length
„„ sealed mechanically fixed joints and connections.
„„
Where ductwork passes through an external wall, it should be positioned to slope slightly outwards to prevent water entering
the building. Clips and supports for ductwork should be spaced at equal distances and in accordance with the ductwork
manufacturer’s recommendations. For rigid ductwork, they should not generally be more than 750mm apart.
Ductwork should not be in direct contact with other surfaces, such as plasterboard ceilings, that may transfer noise to the home.
Terminals
Ventilation systems should terminate freely to open air.
The air flow resistance of terminals should not adversely affect the performance of the ventilation system. Airflow resistance of
terminals can be obtained through testing in accordance with BS EN 13141-2.

terminal extracting
to open air

insulation removed
for clarity

8.1.13 Testing and commissioning

Services shall be tested and commissioned to ensure satisfactory operation.
Services should be tested:
in accordance with all relevant regulations and codes
„„ to ensure leaks or other defects are made good prior to the
„„
of practice application of finish and handover of the home.
where pipes are located under screeds (including air or
„„
water testing before and after the screed is laid)
Before completion and handover of the building services should be commissioned in accordance with relevant regulations and
codes of practice.
8.1
Low or zero carbon
technologies
CHAPTER 8.2
This chapter gives guidance on meeting the
Technical Requirements for low or zero
carbon (LZC) technologies.

8.2.1 Compliance 02
8.2.2 Provision of information 03
8.2.3 Clean Air Act 03
8.2.4 System design 03
8.2.5 Access 04
8.2.6 Handling, storage and protection 04
8.2.7 Sequence of work 04
8.2.8 Location 04
8.2.9 Building integration 04
8.2.10 Fixing 05
8.2.11 Electrical installation requirements 06
8.2.12 Pipes, insulation and protection
from cold 06
8.2.13 Ground collectors 06
8.2.14 Fuel storage 07
8.2.15 Safe discharge 07
8.2.16 Testing and commissioning 07
8.2.17 Handover requirements 07
8.2.18 Further information 07
 2020
Low or zero carbon technologies
1 1
CHAPTER 8.2

Introduction
This chapter provides guidance on low or zero carbon (LZC) technologies acceptable to NHBC. Other systems that
follow the general principles of this chapter may also be acceptable, subject to specific agreement with NHBC.
Additional requirements for solid fuel and oil fired boilers are given in Chapter 6.8 ‘Fireplaces, chimneys and flues’.
Guidance on other internal services is given in Chapter 8.1 ‘Internal services’.
This chapter provides guidance on the following technologies:

Biomass boiler Heat pump

Systems which burn wood pellets or chips for space and/or Systems which transfer heat from low energy sources. The
water heating. most common sources are ground, outdoor air and exhaust air.
input output compressor

evaporator condenser output

expansion pump
vessel
feed
feed

biomass boiler hot water store

ground collector expansion
valve
hot water store

Solar photovoltaics (PV) Solar thermal water heating

Systems which convert solar radiation into electricity. Systems which convert solar radiation energy to space and/or
water heating.
output
(demand)
generation export pump
inverter meter meter

output output
solar
(export) thermal

consumer import
unit meter
PV array expansion
vessel +
relief valve discharge
storage
feed vessel
AC mains supply

boiler hot water store

Wind turbine
Systems which convert wind energy into electricity.
output
8.2

(demand)
generation export
inverter meter meter

output
(export)

consumer import
unit meter

AC mains supply

The illustrations provided within the introduction are generic and do not indicate the only possible systems acceptable to NHBC.
 2020
Low or zero carbon technologies
22
CHAPTER 8.2

Definitions for this chapter

Controls Controls are used to operate and/or regulate the system and may be electrical or mechanical.
Exclusion zone An area where entry is restricted during periods when maintenance is in progress, to prevent risk of
injury or loss of life.
Ground collectors The component of a ground source heat pump system which absorbs heat from the ground.
Collectors can be installed either horizontally or vertically in the ground. They may also be
incorporated into proprietary foundation systems.
Interstitial Condensation caused by vapour from within the building condensing on colder surfaces within the
condensation wall construction, often occurring due to cold bridging.
Inverter A device that converts direct current into alternating current.
Islanding (island Where an LZC technology feeds the network or local distribution system during a planned or
mode operation) unscheduled loss of mains supply.
Low or zero carbon A term applied to renewable sources of energy, and also to technologies which are significantly more
(LZC) technologies efficient than traditional solutions, or which emit less carbon in providing heating, cooling or power.
Open loop A heat pump system that extracts water from an underground source, pumps it through a heat
system stem exchanger and returns it underground.
Parallel electrical A system in which building loads can be fed simultaneously from the national grid or electricity supply
generation grid and on-site sources such as wind turbines and photovoltaic panels.
Performance The manner or quality of functioning for a material, product or system.
Refrigerant pipework Carries refrigerant between the indoor and outdoor unit of a split system. Normally made of copper
and must be insulated and protected from damage.
Renewable energy Energy from naturally available sources that can be replenished, including energy from the sun,
the wind and tides, and from replaceable matter such as wood or other plant material.
Split system A type of heat pump in which the condenser is located indoors, the evaporator is located outdoors,
and the two are linked by refrigerant pipework.
Switchgear The combination of electrical switches, fuses and/or circuit breakers used to isolate electrical
equipment.

8.2.1 Compliance Also see: Chapter 2.1 and www.microgenerationcertification.org

LZC technologies shall comply with the Technical Requirements. Issues to be taken into account include:
a) relevant standards c) operative competency.
b) product certification

LZC technologies that comply with the guidance in this chapter will generally be acceptable.

Relevant standards
LZC should comply with relevant standards including where applicable:

BS EN 12975-1 ‘Thermal solar systems and components. Solar collectors’.

BS EN 12976-1 ‘Thermal solar systems and components. Factory made systems’.
BS EN 61215 ‘Terrestrial photovoltaic (PV) modules - Design qualification and type approval’.
BS EN 14511 Parts 1-4 ‘Air conditioners, liquid chilling packages and heat pumps with electrically driven compressors for
8.2

space heating and cooling’.

BS EN 61400-1 ‘Wind turbines’.
BS EN 61400-2 ‘Wind turbines. Small wind turbines’.
BS EN 14785 ‘Residential space heating appliances fired by wood pellets’.
BS EN 12809 ‘Residential independent boilers fired by solid fuel’.
BS EN 303-5 ‘Heating boilers for solid fuels, hand and automatically fired, nominal heat output of up to 300kW.
Terminology, requirements, testing and marking’.
 2020
Low or zero carbon technologies
33
CHAPTER 8.2

Product certification
LZC technologies should have current certification confirming satisfactory assessment by an appropriate independent authority
acceptable to NHBC.
Systems, products and installations that are assessed through the Microgeneration Certification Scheme (MCS) will generally be
acceptable to NHBC. Certification and test documentation should be made available to NHBC upon request.
Other certification bodies or test documentation may be acceptable where they are considered by NHBC to be a suitable
alternative.

Operative competency
LZC systems should be installed by operatives:
competent and familiar with the system being installed, and
„„ certified to a standard acceptable to NHBC.
„„
Installers who have been trained in accordance with the MCS installer standards will generally be acceptable to NHBC.

8.2.2 Provision of information

Designs and specifications shall be produced in a clearly understandable format, include all relevant
information and be distributed to all appropriate personnel.
Design and specification information should be issued to site supervisors, relevant specialist subcontractors and suppliers,
and include the following information:
Indication of which manufacturer and/or installer is
„„ Interface details.
„„
responsible for each system and interface. Specification for controls.
„„
A full set of current drawings.
„„ On-site testing requirements.
„„
Manufacturers’ specifications.
„„ Commissioning schedule.
„„
Fixing schedule.
„„

8.2.3 Clean Air Act

Biomass boilers installed in smoke controlled areas shall comply with relevant legislation.

Biomass boilers to be installed within a smoke controlled area should comply with the Clean Air Act 1993 or
Clean Air (Northern Ireland) Order 1981.

8.2.4 System design

LZC technologies shall be designed to ensure satisfactory performance. Issues to be taken into
account include:
a) location d) compatibility
b) acoustics e) performance.
c) systems

LZC technologies should be designed in accordance with the manufacturer’s recommendations, certification scheme requirements
and appropriate standards.
8.2

Location
The design and location of LZC technologies should take account of factors such as orientation, roof pitch and shading.
For stand-alone wind turbine systems, suitable exclusion zones should be provided in accordance with the manufacturer’s
recommendations and geographical location.

Acoustics
Design and location should take account of:
internal and external noise
„„ the effect on neighbouring properties, particularly the
„„
vibration
„„ positioning of the LZC technology in relation to openings.
 2020
Low or zero carbon technologies
44
CHAPTER 8.2

Systems
Each system should generally be supplied from one manufacturer as a package and not as individual components or materials.
However, where components from more than one manufacturer are used, they should be compatible to ensure
satisfactory performance.

Compatibility
LZC technologies should be installed so as not to adversely affect the performance of the building to which they are fixed, and in
accordance with the manufacturer’s recommendations.
Multiple systems should be compatible with each other.

Performance
LZC technologies designed to contribute towards space and water heating should be designed in accordance with the
performance requirements in Chapter 8.1 ‘Internal services’.

8.2.5 Access
Appropriate arrangements shall be provided for the purposes of cleaning, inspection, maintenance and
repair of LZC technologies.
Safe access should be provided to the LZC technologies, including switchgear, inverters, meters and controls. This is to
enable the cleaning, inspection, maintenance and repair of systems. Access should be provided in accordance with the
manufacturer’s recommendations.

8.2.6 Handling, storage and protection

Materials, products and systems shall be handled, stored and protected in a satisfactory manner to
prevent damage, distortion, weathering and degradation.
LZC technologies should be:
transported, lifted, handled and stored in accordance with
„„ delivered in sequence to avoid storage
„„
the manufacturer’s recommendations protected to avoid the risk of damage.
„„

8.2.7 Sequence of work

LZC technologies shall be installed in accordance with a suitable schedule.

To ensure performance, certain LZC systems and ancillary components should be installed in a logical and timely sequence in
accordance with the manufacturer’s recommendations.

8.2.8 Location
LZC technologies shall be correctly located.

LZC technologies, including ancillary components should be located and identified in accordance with the
manufacturer’s recommendations.

8.2.9 Building integration

8.2

LZC technologies shall be securely fixed and not adversely affect the weather resistance of the building.

Foundations and anchor points for stand-alone LZC technologies should be designed by an engineer in accordance with Technical
Requirement R5 to withstand the structural forces acting upon them.
The structure to which the LZC technology is attached should be assessed according to its ability to accept the loadings and
prevent detrimental effects arising from movement or vibration. The design of the structure should take account of:
the self-weight of the LZC components
„„ snow loads
„„
imposed loads
„„ dynamic loading (where relevant).
„„
wind loads
„„
 2020
Low or zero carbon technologies
55
CHAPTER 8.2

Notching, drilling or chasing of structural components to

accommodate service pipes or cables should either comply 3D mounted
with Chapter 8.1 ‘Internal services’, or be designed by an
engineer in accordance with Technical Requirement R5. integrated

Fixings, supports, bracketry and mounting frames should:

accommodate all static and dynamic loads in accordance
„„
with the manufacturer’s recommendations
be designed to take account of ventilation and drainage
„„
requirements of the LZC technology
3D
have adequate protection against corrosion.
„„ flashing support
and head flashing
Where two metals are to be joined, they should either be
compatible or isolated, to prevent bimetallic corrosion. solar panel
Aluminium and aluminium alloys should not come into contact
flow – in
with cementitious material.
seal with membrane
flow – out
sill flashing

All interfaces between the LZC technology and the building should ensure adequate weather resistance, sealed to limit air leakage
and prevent moisture from reaching the interior or any part of the structure that could be adversely affected by its presence. The
envelope should be weatherproofed using appropriate flashings and fixings. Weatherproofing details that rely solely on sealant are
not acceptable. Flashings should be formed from the materials listed in Table 1.
Table 1: Materials for flashings
Flashing material Guidance
Rolled lead sheet Minimum code 4. BS EN 12588.
Aluminium and aluminium alloys BS EN 485 and BS EN 573, 0.6-0.9mm thick and protected from contact with mortar by
a coating of bituminous paint.
Zinc alloys BS EN 988 and 0.6mm thick.
Copper BS EN 1172 0.55mm thick and fully annealed. Where two metals are to be joined,
they should be compatible and not cause bimetallic corrosion in that environment
Alternatively, they should be isolated from each other.
Proprietary flashing, Assessed in accordance with Technical Requirement R3.
including plastic and composite.

To avoid potential surface or interstitial condensation, the design should take account of thermal bridging, particularly where any
part of the system, including fixings, penetrates the thermal envelope.

8.2.10 Fixing Also see: Chapter 2.1

LZC technologies shall be fixed using durable materials.
8.2

Fixings should comply with the types listed in Table 2.

Table 2: Materials suitable for fixings
Fixing material Guidance
Phosphor bronze NA
Silicon bronze NA
Stainless steel BS EN ISO 3506
Mild steel Coatings to BS EN ISO 2081, BS EN ISO 2082, BS EN 1461, or other appropriate treatment in
accordance with BS EN ISO 12944 or BS EN ISO 14713.
Aluminium alloy BS EN 573 and BS EN 755
Stainless steel BS EN 10088
Mild steel BS EN 10346
Other materials Assessed in accordance with Technical Requirement R3.
 2020
Low or zero carbon technologies
66
CHAPTER 8.2

Materials that comply with recognised standards, which provide equal or better performance to those above, are also acceptable.
The type, size, number, position and fitting tolerance of fixings should be in accordance with the manufacturer’s recommendations.
Issues that should be taken into account include:
the provision of suitable locking nuts and washers
„„ the isolation of aluminium from cementitious material.
„„
the isolation of dissimilar metals
„„

8.2.11 Electrical installation requirements

The electrical installation shall be in accordance with relevant regulations.

Electrical installations should comply with BS 7671 ‘Requirements for Electrical Installations’.
Where parallel electrical generation occurs, inverters should have a current Engineering Recommendation G83/2 type test
certificate and comply with all other parts of ER G83/2 for standard installations. Larger installations should comply with
ER G59/3-2.
The electrical installation should be capable of being isolated from all other electrical sources when required, for maintenance
or testing.
LZC technologies which generate electricity and are connected to the mains should automatically disconnect when there is a
mains power failure. This is to prevent them from feeding the network or local distribution system during a planned or unscheduled
loss of mains supply. This is known as ‘islanding’.

8.2.12 Pipes, insulation and protection from cold

All pipework and insulation, including refrigerant pipework, shall ensure adequate performance and be
designed to prevent freezing.
Materials used for pipes and insulation should be suitable for the intended purpose and provide satisfactory performance for the
life of the system. Pipes should comply with relevant codes and standards or be independently assessed for their intended use
in accordance with Technical Requirement R3. Insulation materials should be inert, and durable, and should not be adversely
affected by moisture or vapour. They should also comply with relevant codes and standards or be independently assessed for
their intended use in accordance with Technical Requirement R3.
Where there is a risk of pipes freezing, they should be internal unit
insulated, particularly when at, or close to, ground level.
Refrigerant pipework connecting split systems should
heat
be of refrigerant quality copper pipe or other material as provided
to space
recommended by the manufacturer. The pipe should be
insulated, and the insulation should incorporate a vapour
control layer to prevent ice build-up. external unit

Air source systems should incorporate an automatic defrost insulated refrigerant

quality copper pipe
cycle and suitable condensate drainage. heat absorbed
from the
outside air 8.2

8.2.13 Ground collectors

The installation of ground collectors shall take structural and environmental factors into account.

The depth and layout of ground collectors should be specified to avoid freezing of adjacent ground. Where open loop systems are
proposed, consultation with the appropriate environment agency should be made and may require one or more of the following:
A licence to investigate groundwater.
„„ A discharge consent.
„„
An abstraction licence.
„„
Excavations for the installation of ground collectors should not adversely affect aquifers, foundations, drainage, water supply pipes
and other services. Design should take account of local planning authority guidance, including excavations that are close to trees
and hedgerows.
Ground collectors should be protected and tested prior to backfilling.
 2020
Low or zero carbon technologies
77
CHAPTER 8.2

8.2.14 Fuel storage Also see: The HVCA Guide to Good Practice Installation of Biofuel Heating (TR/38)
Fuel storage for biomass boilers shall be suitable for the installation.

Fuel stores should have appropriate:

access for delivery
„„ volume to take account of peak load and period of demand
„„
fire detection and extinguishing equipment where elevated
„„ fire resistance and separation to prevent fire and gases
„„
dust levels are expected entering other parts of the building.

8.2.15 Safe discharge

Discharge from LZC technologies shall terminate safely.

Solar thermal water heating systems should discharge into a storage vessel. The discharge pipework and vessel should be
suitable to withstand high temperatures.

8.2.16 Testing and commissioning

LZC technologies shall be tested and commissioned in accordance with the commissioning schedule.

The installer should check that the system is in accordance with the certification requirements, the manufacturer’s
recommendations and the design. Issues to be taken into account include:
the safety of the system
„„ the correct operation of the system.
„„
the correct installation of the system
„„
Upon completion, the installer should provide a certificate to confirm that the LZC technology has been installed, tested and
commissioned in accordance with the above.

8.2.17 Handover requirements

Detailed information and instructions shall be provided to the homeowner.

The pack of information provided to the homeowner should include:

user instructions for the systems installed
„„ a completed installer’s certificate from an acceptable
„„
contact details for the manufacturer and installer
„„ independent assessment organisation, MCS or
key components installed
„„ suitable alternative
a completed manufacturer’s certificate from an acceptable
„„ details of the fuel type and source
„„
independent assessment organisation, MCS or maintenance and servicing requirements
„„
suitable alternative warranties and/or guarantees for the LZC technology.
„„

8.2.18 Further information

„„
Renewable Energy Association (REA) „„
BS EN ISO 14713-2:2009. Zinc coatings. Guidelines and
„„
CE72 Energy efficiency best practice in housing. Installing recommendations for the protection against corrosion of iron
small wind-powered electricity generating systems: and steel in structures. Hot dip galvanizing
Guidance for installers and specifiers „„
BS EN ISO 14713-3:2017. Zinc coatings. Guidelines and
8.2

„„
ER G59/3-4 Recommendations for the Connection of recommendations for the protection against corrosion of iron
Generating Plant to the Distribution Systems of Licensed and steel in structures. Sherardizing
Distribution Network Operators’ „„
BRE Digest DIG 489 Wind loads on roof-mounted
„„
ER G83/2-1 Recommendations for the Connection of Type photovoltaic and solar thermal systems’.
Tested Small-scale Embedded Generators (Up to 16A per
Phase) in Parallel with Low-Voltage Distribution Systems
„„
BS EN ISO 14713-1:2017. Zinc coatings. Guidelines and
recommendations for the protection against corrosion of
iron and steel in structures. General principles of design and
corrosion resistance
 Mechanical ventilation
with heat recovery
CHAPTER 8.3
This chapter provides guidance on
mechanical ventilation with heat recovery
(MVHR) systems acceptable to NHBC.

8.3.1 Compliance 01
8.3.2 Provision of information 01
8.3.3 Building integration 01
8.3.4 Noise 02
8.3.5 Design considerations 02
8.3.6 Access and operation 04
8.3.7 Ductwork 04
8.3.8 Fixing and jointing of ductwork 04
8.3.9 Commissioning and balancing 05
8.3.10 Handover requirements 05

© Designed and produced by NHBC

 2020
Mechanical ventilation with heat recovery
1 1
CHAPTER 8.3

Definitions for this chapter

Air valve Wall or ceiling mounted fittings used
(extract and supply) to balance the flow rate of air between terminal (exhaust)
rooms; may be referred to as grilles.
terminal (intake)
Exhaust ductwork Carries air from the fan unit and
exhaust ductwork
exhausts it to the external atmosphere.
intake ductwork
Intake ductwork Carries air from the external atmosphere
to the MVHR fan unit.
MVHR fan unit
MVHR fan unit Unit that contains the fan(s),
heat exchanger and filter(s). service ductwork (extract)
Service ductwork Carries air between the air valves and service ductwork (supply)
extract and supply the MVHR fan unit.
air valve (extract)
Terminal fittings Located on the outside of the building to
air valve (supply)
finish the intake and exhaust ductwork.

Also see: Chapter 2.1, Approved Document F, Domestic Ventilation Compliance Guide,
Section 3 of the Technical Handbooks, Domestic Ventilation Guide in Scotland and
8.3.1 Compliance Technical Booklets in Northern Ireland
MVHR design, materials and sitework shall comply with the Technical Requirements, and be installed by
competent operatives.
MVHR systems that comply with the guidance in this chapter and are in accordance with the relevant British Standards and
building regulations will generally be acceptable.
MVHR systems should be installed by operatives:
competent and familiar with the system being installed, and
„„ trained in accordance with the BPEC installer scheme,
„„
or other suitable scheme acceptable to NHBC.

8.3.2 Provision of information

Designs and specifications shall be produced in a clearly understandable format, include all relevant
information and be distributed to the appropriate personnel.
Designs and specifications should be issued to site supervisors, relevant specialist subcontractors and suppliers, and include the
following information:
Location of all ductwork runs, the fan unit and controls.
„„ Type and location of ancillary components, including those
„„
Type, size and position of ducts and terminals.
„„ used for fire safety and acoustic purposes.
Direction of fall for ‘horizontal’ ductwork.
„„ Designed airflow-balancing figures for the system.
„„
Type and spacing of clips and fixings.
„„

8.3.3 Building integration Also see: Chapter 7.1 and 7.2

MVHR systems shall ensure compatibility with other building elements and not adversely affect the
performance of the building. Issues to be taken into account include:
8.3

a) weathertightness c) firestopping.
b) fixing of fan units

Weathertightness
Proprietary roof terminals should be used to ensure the weathertightness of the roof covering.

Fixing of fan units

MVHR fan units should only be fixed to parts of the building capable of taking the load. Where MVHR fan units are supported by
framed structures, additional components such as noggings may be required to provide a secure fixing point.
Fan units should be located, orientated and fixed in accordance with the design, using the clips, brackets and fixings
recommended by the manufacturer.
 2020
Mechanical ventilation with heat recovery
22
CHAPTER 8.3

Firestopping
The MVHR system should not adversely affect the fire performance of the building. Issues to be taken into account include:
ensuring that the fire requirements of the building are in
„„ location and type of firestops to be used
„„
accordance with relevant building regulations integrity of protected stairs and halls
„„
suitable detailing of components passing through other
„„ integrity of walls and floors.
„„
elements of the building
Proprietary fire components should be suitably tested, and specified to take account of the test conditions.
Relevant standards include:
BS 476 ‘Fire tests on building materials and structures.’
BS EN 1365-2 ‘Fire resistance tests for loadbearing elements. Floors and roofs.’
BS EN 1366-3 ‘Fire resistance tests for service installations. Penetration seals.’

8.3.4 Noise
MVHR systems shall be designed to minimise disturbance caused by noise.
MVHR fan units should be sized to run at their optimum speed and to provide suitable performance whilst taking the resulting
noise and vibration into account. Specifying MVHR fan units that can provide the required airflow rates when running at less than
full speed can reduce unnecessary noise.
Ductwork should be sized to allow air to pass freely without causing excessive noise disturbance. To reduce noise transfer
along ductwork, a short length of flexible duct can be installed adjacent to air valves and fan units. Other issues to be taken into
account include:
noise between habitable rooms
„„ location of the MVHR fan unit
„„
external noise
„„ the type of mountings used to secure the MVHR fan unit.
„„

8.3.5 Design considerations Also see: Chapter 9.1

MVHR systems shall ensure compatibility and satisfactory performance. Issues to be taken into
account include:
a) performance d) control of condensation
b) systemised approach e) protection from cold.
c) type and position of air valves and terminals

Performance
The MVHR system should be designed to provide satisfactory performance and be installed according to the design and
manufacturer’s recommendations. Variations from the design should maintain the satisfactory performance of the system and be
approved by the designer.
Issues that should be taken into account include:
ventilation rates as set out in appropriate building
„„ ensuring the even distribution of airflow, taking into account
„„
regulations and standards airflow resistance, including from bends and fittings.
fan capacity, accounting for airflow resistance of
„„
8.3

the system
Airflow resistance should be calculated using figures for air valves and terminals determined in accordance with BS EN 13141-2
and data supplied by the duct manufacturer. Ductwork should be as direct as possible to reduce the number of bends.
Allowance should be made for air transfer within the home. Where gaps between the underside of internal doors and the floor
finish are used for air transfer, the guidance in Chapter 9.1 ‘A consistent approach to finishes’ should be considered.

Systemised approach
The MVHR system should be designed as a complete package, taking into account the performance of all components
and materials, to ensure compatibility and the performance requirements of the system.
Particular consideration should be given where components from different manufacturers are specified on the same system.
 2020
Mechanical ventilation with heat recovery
33
CHAPTER 8.3

Type and position of air valves and terminals

Air valves should be selected according to location and function, ensuring appropriate specification for:
„„ wall or ceiling location „„the velocity of the system.
„„ supply or extract function

To create cross-ventilation within a room and to ensure satisfactory operation, air valves on low velocity systems should be:
positioned on the opposite side of the room from internal
„„ „„ positioned to account for the likely location of tall furniture
door openings and to avoid draughts over beds and seating areas
„„ a minimum of 200mm from walls, where located on a ceiling „„ lockable, where adjustable.
„„ a maximum of 400mm from the ceiling, where located
on a wall
„„ a minimum of 600mm (on plan) from hobs in kitchens

To prevent cross-contamination, intake terminals should generally be separated from exhaust terminals and other potential
sources of pollution by a minimum of 1m measured on plan. Increased separation distances may be required between the intake
and any:
soil and vent pipe terminal
„„ biomass or solid fuel chimney terminal.
„„
boiler flue outlet
„„
Terminals should prevent the entry of birds and animals.

Control of condensation
Ductwork should be insulated to prevent condensation formation where:
it passes through spaces outside the insulated parts of
„„ „„carrying cold air through spaces that are within the insulated
the home, such as a roof void parts of the home.
This can be achieved by using suitable pre-insulated ductwork, or a proprietary insulation system with a thermal resistance
equivalent to a minimum of 25mm of insulating material, with a thermal conductivity of 0.04W/Mk.
Ductwork insulation, including that used for proprietary duct insulation systems and pre-insulated ducts should be:
inert, durable and suitable for use with the ductwork system
„„ installed in a neat and workmanlike manner to ensure that
„„
continuous and vapour resistant
„„ there are no gaps
not adversely affected by moisture vapour
„„ installed in accordance with the
„„
manufacturer’s recommendations.
Where a vapour control layer is incorporated, the joints should be sealed using appropriate tapes or sealants as recommended
by the manufacturer.
Table 1: Ductwork insulation
Type of duct Ductwork continuously insulated
Ductwork located inside the insulated Ductwork located outside the insulated part of
part of the home the home
Intake Yes Yes
Exhaust Yes Yes
Service (supply and extract) No Yes(1)
Notes
8.3

1 Additional insulation should be provided to protect the system from the cold.

Any condensate that forms within the fan unit or ductwork should be able to drain to a suitable outfall. Fan units should be
located to enable connection of the condensate drain to the soil and waste system via a dry trap.

Protection from cold

MVHR systems should be protected from the effects of cold. Issues to be taken into account include:
performance in relation to indoor air quality
„„ „„ insulation of ductwork and other system components.
the manufacturer’s recommendations where any parts are
„„
located outside the insulated part of the home

To prevent damage to the components and ensure satisfactory operation, MVHR systems should be fitted with automatic
frost protection.
 2020
Mechanical ventilation with heat recovery
44
CHAPTER 8.3

Horizontal sections of service ductwork, outside the insulated pre-insulated to achieve a thermal
performance equivalent to at least 25mm
parts of the home, should be insulated to achieve a thermal of insulating material with a thermal
conductivity of 0.04W/Mk
resistance equivalent to at least 150mm of insulating material
with a thermal conductivity of 0.04W/Mk. This may be
achieved by installing the ductwork between the layers
of horizontal insulation.
Condensate drains located outside the insulated part of the
home should be insulated to prevent freezing.
loft insulation used to achieve a total thermal performance
equivalent to at least 150mm of insulating material with
a thermal conductivity of 0.04W/Mk

8.3.6 Access and operation

MVHR systems shall be designed and installed to ensure that the fan unit and associated controls are
easily accessible.
Table 2: Guidance for the suitable functioning of, and access to, the MVHR system
Fan unit located inside the insulated part of Fan unit located outside the insulated part of
the home the home
Access Access should not be obstructed and panels should A safe means of access, including a suitable walkway
be located and sized to enable routine servicing to be and a working platform 1m2 immediately adjacent to the
carried out. MVHR fan unit, should be provided. The walkway and
platform should be designed to ensure the continuity of
any insulation, and the supporting structure should be
designed to take account of the additional load.
Control and Where a ‘boost’ function is provided, it should switch off automatically and be located in, or adjacent to, the room
functionality it serves. Where a ‘summer bypass’ function is provided, it should operate automatically and divert the airflow
around the heat exchanger. The MVHR system should be capable of being isolated by a switched fused spur.
Indication MVHR systems should include visual indicators showing maintenance and servicing requirements, and mode
and controls of operation. These should be visible from within the insulated envelope, not obscured from view,
and be simple to use.
Cleaning To maintain operating performance, extract service ductwork and air valves should either be fitted with filters,
or ductwork should be accessible for cleaning.

8.3.7 Ductwork
Ductwork design and the materials used should be suitable for the intended purpose and not adversely
affect the performance of the building.
Ductwork should:
provide satisfactory performance for the life of the system
„„
be routed as directly as practicable
„„
be of a rigid or semi-rigid material suitable for use in MVHR
„„
systems
be fixed in accordance with the manufacturer’s
„„
recommendations.
air valve
8.3

Bends, connections and junctions should be formed using proprietary components that are part of the ductwork system.
Flexible ducting should:
only be located adjacent to fan units or air valves
„„ not be used to form bends.
„„
not be more than 300mm in length
„„
Where ductwork routes require alterations to structural elements, these should be in accordance with the manufacturer’s
recommendations or in accordance with Technical Requirement R5.

8.3.8 Fixing and jointing of ductwork

MVHR ductwork and insulation shall be installed to a satisfactory standard. Issues to be taken into
account include:
a) fixing b) jointing.
 2020
Mechanical ventilation with heat recovery
55
CHAPTER 8.3

Ductwork should be securely installed in a neat and workmanlike manner.

Fixing
Parallel ductwork runs should be positioned to maintain a reasonably even gap.
To prevent condensate collecting, horizontal ductwork should be to a suitable outfall in accordance with the design, and installed
to a true line to avoid localised dips.
Where ductwork passes through an external wall, it should be positioned to slope slightly outwards to prevent water entering
the building.
Ductwork should be securely held in position by evenly spaced clips no more than 750mm apart, or in accordance with the
ductwork manufacturer’s recommendations.
Ductwork should not be in direct contact with other surfaces, such as plasterboard ceilings, that may transfer noise to the home.

Jointing
The method and materials used for jointing ductwork should be specified by the duct manufacturer, and be:
durable and airtight
„„ sealed with purpose-designed connections in accordance
„„
securely fixed
„„ with the manufacturer’s recommendations.

Where tapes and sealants are used, they should be suitable for the intended purpose and be recommended by the
ductwork manufacturer. Issues to be taken into account in relation to the durability of the jointing method include:
thermal movement
„„ temperature
„„
moisture
„„ compatibility with the duct material.
„„
Tape should be installed in a neat and workmanlike manner, and surfaces should be dry and free from grease and dust
before applying. Excess sealant should not extrude to the inside of the duct.

8.3.9 Commissioning and balancing

MVHR design, materials and sitework shall be tested and commissioned in accordance with the
commissioning schedule.
Upon completion of the installation MVHR systems should be protected from dust during the construction of the home. Where
possible the system should be switched off and dust covers applied to air valves.
Prior to completion of the home, the system:
including ductwork and filters, should be checked to ensure
„„ should be adjusted by using the air valves and controls to
„„
it is clear from dirt and dust that may have accumulated achieve the correct balancing and airflow rates
during construction should have air valves locked in position after correct
„„
should be commissioned to confirm performance
„„ commissioning and balancing.

Where the system cannot be balanced using the air valves and system controls, the complete system should be checked to
ensure that it complies with the design.
Any changes from the design should be referred back to the designer. Adjusting the fan speed above the designed output may
result in noise disturbance, and should be avoided.
A copy of the commissioning certificate should be made available to NHBC upon request.
8.3

8.3.10 Handover requirements

MVHR systems shall be provided with clear and detailed information and instructions that are handed over
to the end user.
The pack of information should be in a format intended for a non-technical user and include:
the commissioning certificate
„„ guidance for the use of summer bypass and boost settings,
„„
user instructions for the system and its controls
„„ where installed
user-friendly description and explanation of the system,
„„ contact details of the manufacturer and installer
„„
including the location of components details of the installed system, including part numbers
„„
details of routine maintenance, e.g. changing/cleaning
„„ for consumables
the filters details of any maintenance and servicing agreements.
„„
method of cleaning the ductwork, where required
„„