Technical Study: CLT Construction
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Key Principles of Detailing CLT in the External Envelope
01 – CLT Internal Leaf
In all applications, the CLT panel must be located on the warm side of insulation. In some instances, this can give designers the opportunity to expose the CLT to the room and gain advantage of its warm and tactile properties. The striking appearance of exposed CLT can be one of the driving factors in pursuing this construction method. In projects that have fire and acoustic requirements, an internal lining will need to be designed and applied to the panel surface – hiding the CLT from view.
The thickness and maximum sizes of the CLT panels will be designed by the structural engineer in conjunction with the CLT manufacturer. Any openings or penetrations in the panels will need to be fully coordinated prior to off site manufacture and as such CLT is well suited to benefit from the use of BIM.
On site handling, installation and protection of the CLT should be undertaken by installers who have experience and understand timber as a construction material. It is important that the CLT be kept dry and that exposure to changing temperature and humidity is avoided. It is also critical to locally protect exposed timber end grain that can be subjected to wetting during construction. The joints and junctions of the CLT panels are typically made airtight with airtightness tape installed on the outer or inner face of the CLT (depending on whether the CLT is exposed or hidden).
02 – Insulation Zone
To achieve the thermal performance required by building regulations, insulation must be added to the CLT panels. The insulation must be located on the outside face of the CLT panels and form a continuous envelope.
It is recommended that the insulation is of a breathable type and that it is protected by a breather membrane on its outer face. Project specific condensation risk analysis calculations should be carried out to verify that no condensation will occur at the insulation/CLT interface.
It is likely that foil faced products may not be breathable and would raise the risk of sustaining moisture within the CLT panel by restricting it from drying to the outside.
03 – Cladding Zone
To protect the envelope from moisture, a well ventilated cavity should be located on the outside of the breather membrane / insulation face. The cavity allows moisture to disperse and any water ingress through the external cladding to drain out away from the construction. The chosen cladding is positioned to the outside of the cavity. There are numerous cladding options available including masonry, timber, render and metal.
Detailing CLT
For an increasing number of projects, CLT can be a great alternative to steel and concrete frame structures. As for any natural wood product, careful detailing is essential to ensure that the structure avoids exposure to sustained moisture during construction and operation. Both the STA (Structual Timber Association) and Trada have released several publications relating to detailing in CLT construction which are recommended reading for anyone looking to design with CLT.
We have created a set of typical envelope details to provide a starting point for detailing a CLT construction.
Download the Details
Many of the details featured here can be downloaded from the Detail Library. For all our CLT details follow the link below. They are available to all members, or can be purchased individually.
DL207 – CLT Foundation Detail Concrete Ground Floor Slab
DL211 – CLT Window Detail with CLT Wall Exposed
DL214 – CLT Intermediate Floor Detail
Recommended Reading
- STA – Advice note 14 – parts 1 to 5 (guidance note series)
- Trada – Cross laminated timber: design and performance (book)
- NHBC – Technical guidance note 6.2/06: cross laminated timber (CLT) construction (guidance note)
- Waugh Thistleton Architects – 100 projects UK CLT (book)
- STA – Laminate / mass timber structures: Moisture protection during construction (guidance note)
- STA – Insulation in the external wall cavity: Good practice checks (guidance note)
- STA – Advice note 18 – Breather membranes to structural timber walls (guidance note)
- Swedish Wood – The CLT Handbook: CLT structures: design and detailing (book)
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Author
Written by Emma Thackstone. Emma is an architect. At the Detail Library, Emma helps the Detail Library with drawing new details and carrying out technical research.
Image Credits
Source URL: https://drmmstudio.com/project/trafalgar-place/
Image URL: https://drmmstudio.com/wp2020/wp-content/uploads/2020/07/trafalgar18-1536×836.jpg
Architect credit: dRMM
Photographer credit: Unknown
Source URL: https://drmmstudio.com/project/trafalgar-place/
Image URL: https://drmmstudio.com/wp2020/wp-content/uploads/2020/07/trafalgar12.jpg
Architect credit: dRMM
Photographer credit: Unknown
Source URL: https://www.ancon.co.uk/products/masonry-support
Image URL: https://www.ancon.co.uk/products/masonry-support
Source URL: https://waughthistleton.com/whitmore-road/
Image URL: https://waughthistleton.com/media/_img/whitmore-road/SS-1-345-PHO-20.jpg.1350x1350_q90.jpg
Architect credit: Waugh Thistleton Architects
Photographer credit: Unknown
Source URL: https://waughthistleton.com/whitmore-road/
Image URL: https://waughthistleton.com/media/_img/whitmore-road/SS-1-345-PHO-44.jpg.1350x1350_q90.jpg
Architect credit: Waugh Thistleton Architects
Photographer credit: Unknown
Source URL: https://hwkarchitects.com/142-Bermondsey-Street
Image URL: https://freight.cargo.site/w/2000/q/75/i/7e16c92ab1cc54ffe350479b00f0cb2330716ca0672205c5d5e473199e40705c/Exterior_11.JPG
Architect credit: HWK Architects
Photographer credit: Unknown
Source URL: https://www.baynesandmitchell.co.uk/command-of-the-oceans.html
Image URL: https://www.baynesandmitchell.co.uk/uploads/1/3/0/6/130608956/bma-command-of-the-oceans-image-2bweb_orig.jpg
Architect credit: Baynes and Mitchell Architects
Photographer credit: Hélène Binet
Source URL: https://www.hughstrange.com/strange-house.html
Image URL: https://www.hughstrange.com/images/strange-house/2-strange-house.jpg
Architect credit: Hugh Strange Architects
Photographer credit: Unknown
Source URL: https://www.dezeen.com/2016/09/27/barretts-grove-wicker-balconies-cross-laminated-timber-housing-amin-taha-architects/
Image URL: https://static.dezeen.com/uploads/2016/09/barretts-grove-groupwork-and-amin-taha-architects-london-uk-residential-architecture_dezeen_2364_col_3-1704×2557.jpg
Architect credit: Groupwork & Amin Taha
Photographer credit: Tim Soar
