Wood Industry and Engineering

ISSN: 2687-6043 e-ISSN: 2687-6035

Year: 2020 Paper Type: Research Article
Volume: 02 Number: 01 Received: 15/10/2020
https://dergipark.org.tr/en/pub/wie Pages: 13 - 16 Accepted: 16/11/2020

THERMAL CONDUCTIVITY OF CROSS LAMINATED TIMBER (CLT) WITH A 45˚
ALTERNATING LAYER CONFIGURATION

Hasan Ozturk1,a Duygu Yucesoy2 Semra Colak2
hasanozturk@ktu.edu.tr duyguycsy@gmail.com colak@ktu.edu.tr
(ORC-ID: 0000-0002-5422-7556) (ORC-ID: 0000-0002-6635-8676) (ORC-ID: 0000-0003-1937-7708)

1Karadeniz Technical University, Arsin Vocational School, Materials and Material Processing Technologies, 61900

Trabzon, Turkey
2Karadeniz Technical University, Department of Forest Industry Engineering, 61080 Trabzon, Turkey

Abstract
Cross-laminated timber (CLT) has increasingly become a viable alternative to other structural
materials, mainly because of its excellent properties related to sustainability, energy efficiency, and speed
of construction. This has resulted in the recent emergence of a significant number of CLT buildings
constructed around the world. Cross-laminated timber panels consist of lumber boards stacked and glued
in layers, which run perpendicular to each other, making them dimensionally stable with high in- and out-
of-plane strength and stiffness. Thermal conductivity is used to estimate the ability of insulation of material.
Thermal conductivity of wood material has varied according to wood species, direction of wood grain,
specific gravity, moisture content, resin type, and addictive members used in manufacture of wood
composite panels. The aim of this study is the comparison of two types of CLT panels consisting of boards
either with grain direction aligned at 45˚ or at 90˚, in terms of their insulation properties. In the study,
spruce (Picea orientalis L.) was used as a wood species, and was used polyurethane for CLT panels. Thermal
conductivity of CLT panels was determined according to ASTM C 518 & ISO 8301. As a result of this study,
it was indicated that thermal conductivity values for 90˚ layers were higher than the values for 45˚ layers.

Keywords: Cross-laminated timber, grain direction, spruce, thermal conductivity

1. Introduction
In facing the global warming trend, there is a dire need for more effective measures to sustain
comfortable temperatures in living environments. To sustain an indoor temperature that is independent of
outdoor temperature fluctuations, materials are needed to be developed that have superior thermal
insulation abilities (Kawasaki and Kawai 2006). Wood has been intensively used as residential construction
material due to its natural beauty and great properties, such as high specific strength, thermal insulation,
and ease of handling and processing (Kilic et al. 2006). For example, wood’s low thermal conductivity and
good strength make it of special interest for building construction, refrigeration, automobile applications,
and cooperage, among others (Gu and Zink-Sharp 2005; Sahin Kol and Altun 2009; Aydin et al., 2015).
Technological improvements in mass timber engineering have created a renewed sense of purpose and a
more versatile use of wood as a building material. Combined with environmental issues, the importance of
wood-based structures is becoming more evident compared with steel and concrete, which in turn will
promote further advancements toward sustainable construction solutions (Fredriksson, 2003; Buck et al.,
2016). Reducing energy consumption of buildings is required in order to counteract global warming
induced by carbon dioxide, and thermal insulation of a building is an important part of this process. One of
the development concepts used in the design of insulation materials is to aim to achieve a low thermal
conductivity (k-value). An alternative development concept is to aim to use environmentally friendly
products (Sekino, 2016).

a Corresponding Author 13
 Öztürk et al. Wood Industry and Engineering, 2, 1 (2020) 13-16

Timber constructions have undergone a revival of popularity over the last years; this positive trend
is associated to a combination of several factors. Firstly, wood-based structural products generate fewer
pollutants compared to the mineral-based building materials (e.g. steel and concrete) because they are
obtained from sustainable and renewable resources. Secondly, timber structural elements are
prefabricated off-site and transported to the building location, where they are quickly assembled. Finally,
the high strength-to-weight ratio of wood is a great advantage for structures erected in seismic-prone areas,
because it limits the total mass of the buildings (Izzi et al., 2018). Cross-laminated timber (CLT) is an
innovative engineering wood panel product made from gluing layers of solid-sawn lumber at perpendicular
angles. Owing to the excellent structural rigidity in both orthogonal directions, CLT becomes a preferred
construction material for shear walls, floor diaphragms, and roof assemblies. CLT is normally made of
Spruce-pine-fir (SPF) lumber or Douglas fir-Larch lumber (He et al., 2018). Cross-laminated timber (CLT)
is an engineered wood product that is playing a major role in the worldwide push for wood buildings taller
than the conventional limit of 5–6 stories for light-frame wood construction (Sullivan et al., 2018). It can
also be combined with other mass timber produces such as glulam beams and columns (Bolvardi et al.,
2018). The higher strength, stiffness, and solid wood volume of CLT, compared to conventional light frame
construction, are the specific characteristics enabling the increased building heights of wood structures
(Sullivan et al., 2018).
With the increasing adversity of climate changes from global warming, discussions within the
international community for establishing an appropriate response policy have become more urgent (Seo et
al., 2011). In facing the global warming trend, there is a dire need for more effective measures to sustain
comfortable temperatures in living environments. To sustain an indoor temperature that is independent of
outdoor temperature fluctuations, materials are needed to be developed that have superior thermal
insulation abilities (Kawasaki and Kawai, 2006). Thermal conductivity is a very important parameter in
determining heat transfer rate and is required for development of thermal insulation of materials (Sahin
Kol and Altun, 2009). Several studies about thermal conductivity of composite materials showed that
thermal conductivity was influenced thickness of composite materials, density, moisture content,
temperature, material space ratio and flow direction of heat (Suleiman et al., 1999; Bader et al., 2007;
Sonderegger and Niemz, 2009; Aydin et al., 2015).
The aim of this study is the comparison of two types of CLT panels consisting of boards either with
grain direction aligned at 45˚ or at 90˚, in terms of their insulation properties. In the study, spruce (Picea
orientalis L.) was used as a wood species, and was used polyurethane for CLT panels. Thermal conductivity
of CLT panels was determined according to ASTM C 518 & ISO 8301.

2. Materials and Methods

In this experimental study, 20 mm-thick lumber with the dimensions of 100 mm by 100 mm were
obtained from Spruce (Picea orientalis L.) logs. The average moisture content was 12±3% as determined by
the oven dry method according to EN 322 (1999). Afterwards, the lumber processed both edgewise and
flatwise through a jointer, the dimensions of each individual board were 16 mm in thickness and 85 mm in
width. Three-layer-CLT panels with 48 mm thick were manufactured by using Polyurethane (PUR) glue
resin. The glue was applied at rate of 160 g/m2 to the single surfaces of lumbers. After gluing, it was formed
CLT panel drafts. The draft of CLT panels is shown in Figure 1. Two types of CLT panels were produced:
transverse layers at 45° and the conventional 90° arrangement. Press pressure was 8 kg/cm2 while pressing
time and temperature were 40 min and 40°C, respectively. Two replicate panels were manufactured for
each test groups. Test samples were conditioned to achieve equilibrium moisture content at 20 °C
temperature and 65% relative humidity prior to testing.

Figure 1: Draft of cross laminated timber

Research Article 14
 Öztürk et al. Wood Industry and Engineering, 2, 1 (2020) 13-16

The thermal conductivity of the cross laminated veneer were determined according to ASTM C 518
& ISO 8301 (2004). The required sample size is 300×300×panel thickness mm. Two specimens were used
for each group. The tests were made at laboratory of Forest Industry Engineering in KTU. The Lasercomp
Fox-314 Heat Flow Meter shown in Figure 2 was used for the determination of thermal conductivity.

Figure 2: Lasercomp Fox-314 heat flow meter

3. Results and Discussion

As a result of this study, it was indicated that thermal conductivity values for 90˚ layers were higher
than the values for 45˚ layers. The thermal conductivity values in the 45° alternating CLT layers was found
to be 0,1015 W/mK and in the 90° alternating CLT layers it was found to be 0,1032 W/mK (Table 1). Wood
is a hygroscopic, porous material. The unique structure of wood causes the anisotropic nature of wood in
its mechanical and physical properties. Thermal conductivity of wood has been studied by many scientists
(Festus et al., 2017). Several studies about thermal conductivity of composite materials showed that
thermal conductivity was influenced thickness of composite materials, density, moisture content,
temperature, material space ratio and flow direction of heat (Suleiman et al., 1999; Bader et al., 2007;
Sonderegger and Niemz, 2009; Aydin et al., 2015). The thermal conductivity of wood varies in the three
main directions of wood as they are usually referred to in the wood lumber industry – Longitudinal
direction (parallel to the grain, along the length of a tree), Radial direction, (perpendicular to the grain,
along the radius of the cross section) and Tangential direction (perpendicular to the grain, tangent to each
growth ring) (Festus et al., 2017).

Table 1: Thermal conductivity values of CLT panels
Groups Thermal Conductivity (W/mK)
45° alternating CLT 0,1015
90° alternating CLT 0,1032


4. Acknowledgments
This study was presented in ORENKO 2018–International Forest Products Congress held by
Karadeniz Technical University, Trabzon.

References
Aydin I., Demir A., and Ozturk H. (2015). Effect of Veneer Drying Temperature on Thermal Conductivity of
Veneer Sheets. Pro Ligno, 11(4), 351-354.
Bader H., Niemz P., and Sonderegger W. (2007). Untersuchungen zum Einfluss des Plattenaufbaus auf
Ausgewählte Eigenschaften von Massivholzplatten. Holzals Roh- und Werkstoff, 65(3), 173–81.
Bolvardi V., Pei S., Lindt J.W. and Dolan J.D. (2018). Direct Displacement Design of Tall Cross Laminated
Timber Platform Buildings with Inter-Story Isolation. Engineering Structures 167, 740–749.
Buck D., Wang X., Hagman O. and Gustafsson A. (2016). Bending Properties of Cross Laminated Timber
(CLT) with a 45° Alternating Layer Configuration. BioResources 11(2), 4633-4644.
Festus T.L., Onah B.T., Okpe B.O. and Josiah O. (2017). The Effect of Temperature and Grain Directions on
the Thermal Conductivity of Woods. International Journal of Advance Research, IJOAR .org, 4(6).

Research Article 15
 Öztürk et al. Wood Industry and Engineering, 2, 1 (2020) 13-16

Fredriksson Y. (2003). Collaboration Between the Wood Component Manufacturers and Large Construction
Companies: A study of Solid Wood Construction. Licentiate thesis. Luleå University of Technology,
Sweden.
Gu H.M and Zink-Sharp A. (2005). Geometric Model for Softwood Transverse Thermal Conductivity. Part 1.
Wood and Fiber Science 37(4), 699-711.
He M., Sun X. and Li Z. (2018). Bending and Compressive Properties of Cross-laminated Timber (CLT) Panels
Made From Canadian Hemlock. Construction and Building Materials 185, 175–183.
Izzi M., Casagrande D., Bezzi S., Pasca D., Follesa M. and Tomasi R. (2018). Seismic Behaviour of Cross
Laminated Timber Structures: A state-of-the-art review, Engineering Structures. 170, 42–52.
Kawasaki T. and Kawai S. (2006). Thermal Insulation Properties of Wood-based Sandwich Panel for Use as
Structural Insulated Walls and Floors. J Wood Sci., 52, 75–83
Kilic Y., Colak M., Baysal E. ans Burdurlu E. (2006). An Investigation of Some Physical and Mechanical
Properties of Laminated Veneer Lumber Manufactured From Black Alder (Alnus glutinosa) Glued with
Polyvinyl Acetate and Polyurethane Adhesives. Forest Products Journal. 56(9), 56-59.
Sahin Kol H. and Altun S. (2009). Effect of Some Chemicals on Thermal Conductivity of Impregnated
Laminated Veneer Lumbers Bonded with Poly(Vinyl Acetate) and Melamine–Formaldehyde
Adhesives. Drying Technology 27,1010–1016.
Sahin Kol H. and Altun S. (2009). Effect of Some Chemicals on Thermal Conductivity of Impregnated
Laminated Veneer Lumbers Bonded with Poly(Vinyl Acetate) and Melamine–Formaldehyde
Adhesives. Drying Technology 27, 1010–1016.
Sekino N. (2016). Density Dependence in The Thermal Conductivity of Cellulose Fiber Mats and Wood
Shavings Mats: Investigation of The Apparent Thermal Conductivity of Coarse Pores, J. Wood Sci., 62,
20–26.
Seo J., Jeon J., Lee J.H. and Kim S. (2011). Thermal Performance Analysis According to Wood Flooring
Structure for Energy Conservation in Radiant Floor Heating Systems. Energy and Buildings 43 (2011)
2039–2042.
Sonderegger W. and Niemz P. (2009). Thermal Conductivity and Water Vapor Transmission Properties of
Wood Based Materials. Eur J Wood Wood Prod., 67, 313–21.
Suleiman B.M., Larfeldt J., Leckner B. and Gustavsson M. (1999). Thermal Conductivity and diffusivity of
wood. Wood Sci Technol, 33(6):465–73.
Sullivana K., Miller T. H. and Gupta R. (2018). Behavior of Cross-laminated Timber Diaphragm Connections
with Self-tapping Screws. Engineering Structures. 168, 505–524.
TS EN 322, (1999). Wood-based panels-Determination of moisture content. Turkish Standards Institute,
Ankara.

Research Article 16