Wood fibre insulation: CLT Applications


Typical section showing key components

XLam wood fibre insulation
Cross Laminated Timber (CLT or 'Crosslam' or 'Xlam') panels as well as other forms of pre-fabricated solid timber walls are becoming more common in the UK. A number of high-profile buildings (eg Stadthaus, Murray Grove ) have recently been completed to demonstrate the way in which structures can be simply assembled using the technique.

Timber panels continue to be supplied usually by German or Austrian manufacturers - this being largely due to the vastly increased availability of raw materials in those countries.

In terms of thermal efficiency and low environmental impact, there's a lot going for structural timber panels. By the very nature of their manufacture, the tight tolerances associated with pre-fabrication are closely associated with high performance building. Thermal bridging is inherently reduced and airtightness is much easier to achieve than through other forms of in-situ construction.

Solid timber walls on their own provide only mediocre rates of thermal transmission, so in most cases insulation needs to be added - usually to the external face of the timber. When using wood fibre insulation to get to low u-values, quite large sections are needed. Where ventilated cladding is proposed, a convenient method is to use I-joists to provide the depth of material as well as minimising thermal bridging. Solutions for rendered finishes are more straightforward through the use of thick sections of rigid wood fibre insulation designed to take render.

In the examples shown below, we have added an internal layer in the form of plasterboard or similar in front of a service zone. Chasing into solid timber needs quite a bit of fore-thought to anticipate future requirements. Adding a service zone provides relief from this anxiety - it also permits for a more flexible range of finishes. In the case of such and internal lining, the vapour control / air tightness layer can be laid across the internal face of the timber. However, should you go for the appearance of the natural timber or need easy access to thermal mass, the membrane can be brought forward to the outside face of the timber panel.

 

Examples of low u-value applications

xlam timber wood fibre weatherboard cladding
download (xlam1.skp)
CLT/ I-joists / sheathing / horizontal timber boarding

• 12.5mm plasterboard and skim (or mineral / clay boards)
• 38mm service void
Vapour control/ airtightness membrane
94mm Cross Laminated Timber wall (0.72 W/mK)
• 220mm I-joists infilled with flexible woodfibre batts (0.038 W/mK)
• 60mm rigid wood fibre sheathing (0.043 W/mK)
• Ventilated cavity
• Horizontal timber board cladding

Approx U-value = 0.15 (subject to specification)
xlam timber wood fibre vertical weatherboard cladding
download (xlam2.skp)
CLT/ I-joists / sheathing / vertical timber boarding

• 12.5mm plasterboard and skim (or mineral / clay boards)
• 38mm service void
Vapour control/ airtightness membrane
94mm Cross Laminated Timber wall (0.72 W/mK)
• 220mm I-joists infilled with flexible woodfibre batts (0.038 W/mK)
• 60mm rigid wood fibre sheathing (0.043 W/mK)
• Ventilated cavity
• Vertical timber board cladding

Approx U-value = 0.15 (subject to specification)
xlam timber wood fibre render
download (xlam3.skp)
CLT / rigid insulation / render

• 12.5mm plasterboard and skim (or mineral / clay boards)
• 38mm service void
Vapour control/ airtightness membrane
94mm Cross Laminated Timber wall (0.72 W/mK)
• 200mm wood fibre insulation (0.038 W/mK)
Lime or polymer (vapour permeable) render

Approx U-value = 0.18 (subject to specification)

 

 

 

 

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