Plywood Used in So Many Different Ways: Eaturing Lywood in Uildings
Plywood Used in So Many Different Ways: Eaturing Lywood in Uildings
Plywood Used in So Many Different Ways: Eaturing Lywood in Uildings
Table of Contents
Introduction ........................................................................................................ 3
Plywood Characteristics ...................................................................................... 3
Cross Laminated Two Way Strength and Stability ......................................................... 3
Face Quality ................................................................................................................... 4
Quality Guaranteed........................................................................................................ 4
When you specify plywood be sure it has the PAA certification mark .......................... 5
Glue Bond....................................................................................................................... 6
Curving Plywood ............................................................................................................ 7
Acoustics and Sound Insulation ..................................................................................... 7
Thermal Performance .................................................................................................... 8
Lightweight panels ......................................................................................................... 9
Fire Hazard Properties ................................................................................................... 9
Floor Material And Coverings ........................................................................................ 9
Wall and Ceiling Linings ............................................................................................... 10
Other Materials ............................................................................................................ 10
Energy Costs of Construction ....................................................................................... 10
Revision History................................................................................................. 22
Introduction
Plywood products are part of a quiet revolution occurring in residential and light commercial
building practices. With low costs, good looks and superior structural performance real wood
plywood products are being used creatively as exterior cladding, decorative flooring, interior wall
and ceiling linings, and as a lightweight, but strong roofing substrate. This brochure provides
guidance on the use of plywood cladding, lining and roofing.
For flooring, and applications such as bracing and box beams, please refer to the relevant EWPAA
publications, available from the EWPAA Web Site.
Plywood Characteristics
Apart from the style and warmth of real timber, plywood has many added advantages
Face Quality
Plywood can be ordered with face veneers to suit the application. Veneer quality A is a high quality
appearance grade suitable for clear finishing. Veneer quality S defines an appearance grade which
permits natural characteristics such as knots as a decorative feature. Veneer quality B is an
appearance grade suitable for high quality paint finishing. Veneer quality C is a non-appearance
grade with a sanded solid surface i.e. all open defects are filled. Finally veneer quality D can have
open defects and would normally be used as a back veneer on a plywood panel. Thus for a clear
finished aesthetic application requiring one viewed surface AD grade plywood would be specified.
Under similar circumstances if a painted finish is required then a minimum of BD grade is the
specification. A choice of timber species other than pine for outer veneers is also available.
Quality Guaranteed
For guaranteed compliance and
reliability specify that the
plywood used must be branded
with the appropriate EWPAA
product certification stamp. This
stamp certifies the product has
been manufactured under a
formalised process based quality
control program and is therefore
fit for use as described in this
literature.
When you specify plywood be sure it has the PAA certification mark
The EWPAA has been accredited by the Joint Accreditation System of Australia and New Zealand
(JAS-ANZ), the peak accreditation body in both countries established by government treaty, as a
product certification body for plywood and other glued structural veneer products. Plywood
cladding, lining and roofing manufactured under the EWPAA quality brand stamp assures product
conformance to the relevant product standard.
Glue Bond
Structural plywood manufactured to
AS/NZS 2269 has a permanent Type A
phenolic bond which is distinctively dark in
colour. Exterior plywood to AS/NZS 2271
can be ordered with the Type A bond.
Phenolic bonds are generally cross linked
polymer chains made from measured
amounts of phenol and formaldehyde. Once
formed and cured these polymers are new
chemical entities, and are extremely stable
and do not break down into phenol and
formaldehyde. These A bonds do not
deteriorate under wet conditions, hot or
cold, thus are suitable for long term
permanent exposure. The plywood however
may need to be preservative treated, when
exposed to the weather or used in damp
conditions, to prevent fungal attack to the
wood. Marine plywood is manufactured
with the same permanent Type A bond.
Apart from making an excellent durable
glue bond for wood products, plywood
products bonded with phenolic bonds have
formaldehyde emissions of 0.00 0.03ppm,
well below the internationally accepted
recommended E1 emission level of 0.1ppm.
These values were established on large
scale chamber tests carried out by the
American Plywood Association and
Hardwood Plywood Manufactures
Association in USA, and verified in Australia
on locally produced plywood.
The Type B bond is an alternative bond used in exterior plywood to AS/NZS2271 and is achieved
using melamine fortified urea formaldehyde adhesive which is light in colour. This adhesive is semi
durable and can only be used in semi exposed conditions such as exterior door skins. This bond
should not be specified if ambient conditions exceed 50oC or 18% moisture content.
The Type C and D bonds used in interior plywood to AS/NZS 2270 are formed using light coloured
urea formaldehyde adhesive, the Type C being more concentrated to meet the requirements of
humid applications. These bonds are not durable in exposed conditions or conditions of moisture
and/or high temperature. However, if used in the correct dry interior environment such as a nonstructural interior panelling, tests have proven the modern resins used for the bonds are durable,
and can provide plywoods that meet the E1 formaldehyde emission requirements.
Curving Plywood
Plywood can be safely curved for
applications such as ceilings and feature
walls. Table one provides guidance for
the minimum recommended radii. Two
factors should be considered before
selecting the plywood thickness. Firstly,
the amount of force and hence the
increased fixings that are required to pull
and hold the panel in tight radius;
thicker panels require considerable force
particularly in thickness above 12mm.
secondly, with tighter radii the change of
radii between the ends of each sheet
(which tend to be straighter) and the
balance of the panel becomes more
visually obvious. Therefore for tighter
radii it is best to use thinner plywoods
and closer supports.
Table 1 : Recommended minimum bending
radii for plywood linings
Normal
Along face
Across face
Thickness
(m)
(m)
(mm)
4.5
7
11
0.6
1.8
1.0
9
12
15
17
2.3
3.6
4.6
6.0
1.3
2.4
3.0
4.4
Thermal Performance
The real advantage of lightweight timber
construction in a subtropical or tropical climate
is the ability to provide very liveable buildings
with wall systems having low thermal mass.
Thus in the cool of the evening following a hot
day the wall will cool rapidly and not keep
heating the interior. Walls with high thermal
mass hold substantially more heat thus
continue to radiate heat in the evening.
In cooler climates, or if the building is to be air
conditioned, the addition of insulation to the
timber structure can provide equivalent
thermal insulation to solid construction. For
example the addition of R1.5 batts into a
plywood clad with reflective sisalation on
90mm studs will result in a wall with an
average R exceeding 2.2 (see table 2).
Therefore, in winter a lightweight timber can
be a very effective insulator and keep the
warmth inside the building.
R Value (m c/Watt
Through
Through
Insulation
Stud
Zone
0.04
0.04
0.08
0.08
0.58
1.50
0.62
0.04
0.04
0.12
0.12
2.36
0.90
Note:
As a non-reflective 20mm air gap has an R value of 0.15, an insulation wall system without
sisalation would reduce the total r value from 2.36 to 1.93 in the above table.
Lightweight panels
Plywood is strong enough to do the job but still light enough to be installed by one person,
saving time and money. The density of pine plywood is around 590kg/m3, thus a 2400 x 1200 x
12mm plywood panel weighs approximately 20kg. Hardwood plywood may be up to 40% more
dense than pine plywood.
Thickness
CRF
15mm or greater
17mm or greater
17mm or greater
Between
2.2 and 4.5
Smoke Development
Rate
Less than 750
percent-minutes
Group
No.
Average Specific
Extinction Area
2
(m /kg)
6mm or greater
< 250
6mm or greater
< 250
Pine, Hoop
6mm or greater
82.4
Pine, Slash
6mm or greater
96.0
Plywood
Species
Other Materials
Face Veneer Common
Name
Botanical Name
Spread of Flame
Index (0-10)
Smoke
Developed Index
(0-10)
Klinkii pine
Aurancaria hunsteinii
Radiata Pine
Pinus radiata
Pinus radiata
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Durability Requirements
The two most important characteristics for
guaranteed long term performance of
plywood as exterior cladding are treatment
against fungal and insect attack, and the
panel be manufactured with permanent
Type A bonds. The preservation treatment
should be a minimum of hazard level H3
outdoors above ground as defined by
AS/NZS1604.3. The preservative treatment
currently available are Ruply and
Ammoniacial Copper Quaternary
Compounds (ACQ) , veneer treatment
systems, and a number of pressure
treatments for finished panels, including
Copper Chrome Arsenate (CCA) and Light
Organic Solvent Preservatives (LOSP) .
Structural plywood to AS/NZS2269 has a Type A bond, and exterior plywood to AS/NZS2271 can be
ordered with Type A bonds. For maximum cost effectiveness it is good practice to use structural
plywood as a wall bracing as well as cladding.
For maximum long term performance to exposed face of the plywood cladding should be finished
with a water repellent or a 100% acrylic latex paint system. Additionally, the edges of the plywood
panel should be sealed to minimise water uptake in the end grain. The edge sealing can be done
using a water repellent or the same primer used on the face, and is most readily applied while the
plywood is in a pack, before installation. Some plywood cladding products presently available in the
marketplace have a machined or textured face veneer which provides a good surface to hold paint,
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reduces and disguises any surface checking of the face veneer effectively by dispersing or reflecting
the incidence of solar radiation.
Installation
Typically, plywood cladding
products are manufactured to suit
1200mm cover with shiplapped or
other machines joints, thus the
studs need to be at 600mm or
400mm centres. These shiplap
joints allow for some panel
movement. If square edged panels
are used, leave a 2-3mm gap
between joints on studs to
accommodate panel movement due
to moisture changes.
The length of standard plywood cladding products available are 2440mm, 2700mm, 2745mm with
3050mm sheets having limited availability. Other panel sizes are available subject to special
enquiry.
Plywood claddings are normally installed vertically, but may also be placed horizontally (i.e. long
dimension across the studs) if horizontal studs are nogged and detailed to prevent water ingress
through the joints. Noggings are not required for vertical installation of plywood cladding, unless it
is under a horizontal joint. The minimum plywood thickness for external cladding are given in table
4 , and the minimum recommended fastener sizes are given in table 5.
Table 4: Minimum plywood thickness (mm) for external cladding
Stud Spacing (mm)
Plywood face grain running
Plywood face grain running
vertically
horizontally
Plywood
Stress Grade
400/450
600
900
400/450
600
900
F11
12
12
17
12
F14
12
12
16
12
Up to 7mm
Up to 21mm
Nails to timber
Screws to timber
No.8 x 30mm
No.8 x 40mm
Screws to steel
No.10 x 45mm
No.10 x 45mm
Notes:
1. Nails are flathead, and screws are self drilling countersunk head.
2. Fasteners must be no-staining and corrosion protected. For some applications stainless steel
or silicon bronze fasteners may be required.
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It is essential in plywood cladding installation that all joints are weatherproofed using shiplapped
joints, battened joints, caulking, flashing timber or elastomeric sealants. Shiplap joints are best
installed facing away from the prevailing weather. The use of sisalation or building paper is
optional, however, when butt or horizontal joints are utilised, or the framing is steel, the use of this
extra protection is recommended. Where used, sisalation must be of the vapour permeable type.
To allow for movement in the panel due to excessive wetting during rainy periods, a 2-3mm gap
must be provided at all panel edges.
Bracing Resistance of
Plywood Exterior Cladding
Plywood cladding fixed to timber
stud walls, in accordance with all
of the requirements of the
EWPAA Structural Plywood Wall
Bracing Manual (available from
the EWPAA Web Site) will
provide, depending on spacings
and connection to the sub floor,
from 3.0kN/m of bracing
resistance per 900mm of clad
wall length.
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14
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Finishing
The plywood surface must be protected to avoid mechanical breakdown (surface checking) and
maximise its appearance and durability. High quality oil based exterior wood stains or 100% acrylic
latex paint systems are recommended. Always use a reputable paint brand as cheaper alternatives
do not always perform. Light colours are recommended in preference to darker colours as they give
superior performance. In humid areas where mould may grow on the paint surface the use of
quality mouldicide in the paint is recommended.
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Plywood Specification
If the lining is designed to have a secondary
as a bracing or a structural diaphragm the
plywood must be structural plywood to
AS/NZS2269. However, for non structural
lining applications completely protected from
the weather any plywood product with
appropriate face veneer is acceptable. The
plywood must be manufactured to a
minimum of AS/NZS2270.
The appearance of decorative veneer varies
considerably depending on species, timber
source and the method of veneering and
plywood manufacturer. Most plywood lining
in the marketplace has attractive rotary
peeled pine veneer faces; however, some
sliced veneers are available and can be
specially matched for colour and figure. The
face veneers are sanded smooth ready for
the selected surface finish. The back side of
the decorative plywood normally is nondecorative and is of reduced quality.
For ceilings, 9mm and 12mm plywood linings
are available with tongued and grooved
edges to negate the need for nogging under
the panel sides. If square edged panels are
used framing is required to support all edges.
Recommended minimum plywood thicknesses are given in table 6. Standard panel size is 2400mm
x 1200mm. 2700mm x 1200mm panels are not as readily available.
Installation
To minimise shrinkage or expansion of panels after installation, it is good practice to let the
plywood panels acclimatise to room temperature and humidity for several days before final fixing.
This is best achieved by breaking open the packs and laying out the panels to allow air to circulate
around them.
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Wall Lining
4mm
6mm
Ceiling lining
6mm
6mm
9mm
12mm
Note: for ceiling lining the face grain must run across the span.
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Bracing Resistance
2.1kN/m
5.3kN/m
Notes:
1. Nails a minimum of 2.5mm diameter x 40mm bullet head.
2. Studs spaced at a maximum of 600mm centres.
3. Structural elastomeric adhesive that meets American Plywood Association Standard AFG-01.
4. Bracing Resistance applies to panels a minimum of 900mm width and a maximum wall height
of 2700mm.
5. Fixing of the bottom plate to the sub-floor can be nominal nailing for the 2.1 kN/m system but
for the 5.3kN/m system the fixing must be strapped or bolted at a minimum of 1200mm
centres as detailed in the EWPAA Structural Plywood Wall Bracing Manual which is available
from the EWPAA Web Site.
Finishing
High quality paints, stains, or clear
finishes are recommended for plywood
linings. Tinted clear finishes e.g. liming
grey, allow decorators to create a
modern coloured key timber dcor.
The use of high gloss finishes and
paints tend to highlight naturally
occurring and manufacturing
characteristics of plywood such as
changes in grain and beat marks from
the sanding. Matt finishes and paints
are recommended to provide a natural
timber finish.
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Plywood Specification
The plywood to be used is CD or DD grade T&G structural plywood to AS/NZS2269. Specialised T&G
plywood with a decorative underside, usually V grooved to give a planked effect, can be used as a
combined structural roof and decorative ceiling. Square edged plywood can be used but will require
nogging under the side joints.
Roofing Overlay
The roofing overlay must be waterproof and durable. It may be decorated asphalt or fibreglass
shingles, timber shakes or shingles, rubber, acrylic or bitumen membranes or metal tiles or decking.
Installation
The two major requirements for the T&G structural plywood are the face must run across i.e.
perpendicular to, the rafters or trusses, and the plywood must be continuous over two or more
spans. The plywood should be installed with 2-3mm gap at all sheet edges, the appropriate fixings
are given in Table 8, and the minimum plywood thickness relative to truss or rafter spacing are
listed in Table 9.
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33 metres/second
41 metres/second
Non Cyclonic
150
100
150
100
100
(for 1200mm spans)
50
(for 1200mm spans)
150
(for 900mm & 800mm spans)
75
( for 900 & 800mm spans)
150
100
Notes:
1. The above fixings are applicable to timber species with joint strength J4 and JD4 and to plywood up to
21mm in thickness.
2. For higher wind speeds or cyclone sites fixings are to be designed for uplift in accordance with
AS/NZS1170.2 wind actions.
Table 9: Allowable structural plywood thickness and rafter spacing for plywood non-trafficable
roofs supporting light weight roofing systems (20kg/m2 max.)
Rafter or Truss
Spacing (mm)
800
900
1200
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Revision History
Revision
4
3.0
2.0
1.0
Changes
Updated logos and member list
Updated to include latest JAS-ANZ Logos
Fixed missing fastener description for installation of exterior
cladding.
Reformatted.
Updated several pictures.
Updated Fire resistance information
Initial Release
Date
Who
07-02-12
MB
18-12-08
MB
28-10-08
MB
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EWPAA Members
Location
Phone
Fax
Web
Australia / NSW
Australia / QLD
Australia / NSW
Australia / SA
www.ausply.com
www.australply.com.au
www.bigrivertimbers.com.au
www.bwp.com.au
Australia / Vic
www.chhwoodlogic.com.au
Australia / SA
New Zealand
www.chhfuturebuild.com
New Zealand
www.shadowclad.co.nz
www.ecoply.co.nz
Fiji
New Zealand
New Zealand
New Zealand
New Zealand
PNG
PNG
Fiji
Australia / WA
www.chhfuturebuild.com
www.nelsonpine.co.nz
www.pngfp.com
www.rhpng.com.pg
www.wesbeam.com,
Location
Australia / Vic
Australia / NSW
Australia / NSW
Australia / TAS
Phone
Fax
Web
www.alpinemdf.com.au
www.chhwoodlogic.com.au
www.drhenderson.com.au
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