A gap, or no gap depends on the exact type of insulation used, the outer skin construction and your location (exposure) in the country. I values aside.
50mm or 100mm kingspan in cavity wall
- Thread starter ey143
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The fabric of the building will soak up and discharge the moisture. As to whether it's sufficient, consult the regs (part L) and use either a standard table for your typical wall buildup or an online U value calc if your buildup is odd, and check it amtches the requirement for the work youre doing
As said, you're not supposed to full fill a cavity wall with rigid insulation. Also as said, there is a product that will full fill a cavity - have specified and used this in several recent projects. The critical thing is that the product has an outer plastic layer which incorporates spacers to maintain a small cavity against the outer leaf. It does bump up the u-value of the wall but I can confirm that bricklayers aren't keen on it. They couldn't say exactly why, when asked, just that they didn't like it.
www.cavitytherm.com
www.cavitytherm.com
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Its not the foam its the rotten square edge jointing system. If you fill the cavity with ordinary square edged foam, you are hoping that the tape will repell any water that migrates through the bricks, so it stays on the brick side of the foam. As the foam is not guaranteed to be non shrinking, but is just quoted as less then 1% shrinkage, over the years the joints will open up. The tape will part company with the foam surface and you will have a nice wicking path for moisture. The foam should be a lot smaller, say 1m square so it is on a pallet and stays flat. It could have a thin layer of plastic/sarking material on its front face, which has a loose overlap on one side and the bottom, so when used its like a tiled roof where the overlap protects the joint underneath it from water ingress. or it could be moulded with a series of grooves along all sides so the blocks interlock, then by putting the correct angles on the edges water would be direct back towards the front. It would be difficult to trim and take around corners.
So the building regs stick to their 2" clear cavity, despite it not being done in the rest of Europe.
Frank
So the building regs stick to their 2" clear cavity, despite it not being done in the rest of Europe.
Frank
It's used quite a lot round here with random stone as it saves building a backing wall. The edges are different to the normal boards.
Jeds, some trowels don't like it as they like a 50mm cavity. Does make it harder laying to the line getting your fingers off the back of the brick.
Jeds, some trowels don't like it as they like a 50mm cavity. Does make it harder laying to the line getting your fingers off the back of the brick.
Random stone walls is where I first came across it. As you say it saves having to build a backing wall, which is a bonus. I then had a job that scraped the SAP by a very small fraction with a 24kW combi boiler - not ideal in a large 4 bed house. I altered the spec to use this cavi stuff and that gave us enough to fit a 36kW Greenstar combi or a system boiler with a megaflow.
If you are not supposed to completely fill a cavity, how is it then that those companies who do cavity wall insulation by drilling holes and pumping fluffy fibers into it, managing to do it?
What's the difference between part filling a new extension wall v a 1930s existing side wall?
What's the difference between part filling a new extension wall v a 1930s existing side wall?
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Water can run down the board and enter where the boards join, unless the correct board is used which has a spigot on the edges to interlock and prevent this. Normally used on random thickness stonework so when thinner stones are used you can fill in to the boards. Before these were available you needed a block backing wall to work to.
Full fill cavity batts and blown in are treated to stop moisture according to the manufacturers.
Full fill cavity batts and blown in are treated to stop moisture according to the manufacturers.
Most of the water would run off, but there is a chance of some getting in at the joints so the boards with spigots are used on a full fill to make sure.
Ordinary boards are not always dead flush with each other so there can also be a bit of a lip on them.
Ordinary boards are not always dead flush with each other so there can also be a bit of a lip on them.
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