KayleyH Posted March 8, 2023 Share Posted March 8, 2023 For our extension which is mainly timber frame but with a couple of brick walls, the timber frame company and building regs have calculated double skin bricks with 50 mm cavity filled with 50 mm rockwall. I don’t know anything about building, but presumed the reason you have a cavity between the 2 layers of bricks was so that water couldn’t cross from the outer bricks to the inner bricks … so I have queried it, and all the advice I’m getting it that it’s fine and water doesnt cross with the rockwall? Anyone had experience on this one way or the other … am hoping I am worrying for no reason, thank you in advance. Link to comment Share on other sites More sharing options...
LA3222 Posted March 8, 2023 Share Posted March 8, 2023 Pretty sure that whenever timber frame is involved there needs to be a minimum 50mm ventilation cavity. Link to comment Share on other sites More sharing options...
ADLIan Posted March 8, 2023 Share Posted March 8, 2023 50mm mineral wool slab in brick/brick cavity wall is woefully inadequate. Would expect at least 100mm, probably 150mm under 2021 version of Appr Doc L. As above, timber frame can be insulated in cavity but 50mm clear cavity must be left assuming masonry outer. Link to comment Share on other sites More sharing options...
joe90 Posted March 8, 2023 Share Posted March 8, 2023 I have used Rockwall slabs in a brick block full fill cavity and can confirm no moisture absorbed, in fact the stuff has a bba certificate for full fill cavity, my cavity was 200mm tho 🤷♂️ Link to comment Share on other sites More sharing options...
ETC Posted March 8, 2023 Share Posted March 8, 2023 1 hour ago, KayleyH said: For our extension which is mainly timber frame but with a couple of brick walls, the timber frame company and building regs have calculated double skin bricks with 50 mm cavity filled with 50 mm rockwall. I don’t know anything about building, but presumed the reason you have a cavity between the 2 layers of bricks was so that water couldn’t cross from the outer bricks to the inner bricks … so I have queried it, and all the advice I’m getting it that it’s fine and water doesnt cross with the rockwall? Anyone had experience on this one way or the other … am hoping I am worrying for no reason, thank you in advance. Why have you mixed timber frame with a masonry cavity wall construction? Timber frame will mostly get its thermal protection from insulation in the inner frame. 50mm Rockwool seems a bit thin for a cavity wall to achieve any decent U-Value. However - if the BBA Certificate says it can be used with brick then it can. Check out the BBA Certificate. Link to comment Share on other sites More sharing options...
joe90 Posted March 8, 2023 Share Posted March 8, 2023 Water resistance — the product will resist the transfer of water across the cavity and may be used in any exposure zone in suitably-constructed walls (see sections 4 and 7). https://www.rockwool.com/syssiteassets/rw-uk/downloads/certificates/rockwool-thermal-insulation-cavity-batt-bba-certificate-15-5237-full-fill-cavity-wall-insulation.pdf 👍 Link to comment Share on other sites More sharing options...
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