Minimum Cavity Size
- Thread starter theDIYkid
- Start date
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what you mean 2 skins with no cavity?
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Really daft question so sorry about this, I bought some knauf cavity slabs 100mm, you can compress it easy so I can get it into a 50mm cavity, is that ok to do that? I mean compress to fir in a smaller cavity as to what its says which is for a 100mm cavity?
Just means more compressed.
You will actually increase the density by compressing the insulation and reduce the thermal performance. 50mm thick insulation will be more efficient.
Great thanks 50mm into 50mm.
No matter how you try and achieve the thermal resistance with masonry, it all ends up being around 300mm thick in any case.
Your only hope of gaining extra space via the solid masonry route is to involve EWI and render (
), if you must. The alternative is fitting insulation (75mm ish) to the interior of the room - doubly horrendous when you consider fixing anything to the walls later on.With such a small extension 8x8feet(?) I would be OK with accepting 50mm, possibly with an increase in insulation in the roof and/or floor as a trade off if practical or even topping up the existing roof. You can do an average U value calc but for such a small extension it doesn't really warrant it, but this would need to confirmed with building control.No matter how you try and achieve the thermal resistance with masonry, it all ends up being around 300mm thick in any case.
Your only hope of gaining extra space via the solid masonry route is to involve EWI and render (
Why would a small extension not benefit from the latest Building Regulations? I'm not getting this.. because it's small I can dodge the reg's.. thing?
I've not met a BCO that says it's ok to dodge the reg's because its small, either lol.
Not dodging it, a simple way of showing compliance is to use the U values stated in a table, however you can adopt other approaches ie average U value calcs, this allws you to compensate for reduced insulation in one element by increasing other elements, but for such a small extension I would make a judgement, for example increasing the insulation in the roof of the proposed work, topping up the roof of the existing house or having insulation blown in the wall of the existing walls. Its about reducing CO2 emissions.
What you have to appreciate the approved documents are a method of showing compliance, they are not regulations.
What you have to appreciate the approved documents are a method of showing compliance, they are not regulations.
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