Upvc shiplap cladding

25 Aug 2016
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United Kingdom
Hi all,

I need to clad the Gable wall and dormers on our new extension. I'm going to use 150mm upvc shiplap, for the Gable wall which is block work with 100mm cavity I'm assuming I should batten the block work with for example tile lats so i can hidden nail the shiplap on, should I put a layer of visqueen dpm over the lats before the shiplap?

The dormers are built from cls and boarded with osb, this is then covered by the roofing felt, should I again batten the osb to fix the shiplap too or can I pin it straight to the osb? I'm assuming no visqueen would be required on the dormers as they are already covered with breathable felt?

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No need for any membrane on a masonry wall.

Is the planned plastic cladding compliant for fire resistance and flame spread?
Be careful with uPVC cladding. The thermal coefficient of expansion of uPVC is horrible. Typically 0.07mm/degree/m To give you an idea a 4m length between deep winter (say -5) and high summer with the sun beating down (say 40 degrees surface temp) is 0.07 x 4 x45 = 12.6mm

Personally, I would never use it. Better to use cement board planks (cembrit, hardie). Usually Breathable membrane then battens then fixings. You use special screws, gecko gauges for fitting and a guillotine to cut. Much nicer, albeit slightly more expensive product.
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Building inspector hasn't made any mention of issues regarding fire suitability.

I'll definitely be using the cladding as it matches the other 2 gables of the house that have had it for 20 years


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