Cavity wall & insulation (extension)

10 Apr 2007
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United Kingdom
So, the garden currently looks like the Somme. Managed to get a 3/4 tonne digger in over the weekend and if it wasn't for the massive lump of concrete found underground, everything would have gone fairly smoothly!

Anyway, I need to shutter off the crater that's left and I've seen some people mentioning 150mm cavity with full fill Rockwool or similar?

I have dug the majority of the footings 600mm so I was intending on 100mm block, 100mm cavity, 50mm partial fill celotex (or similar) and either 100mm internal block or thermalite? Could I go 75mm batts and have a 25mm air gap still?

Is there a nack to thermalite as they seem to draw in the moisture quicker and move about a bit, puts me off using them a bit but I'm guessing they will be needed to keep the U value down with partial fill?

Appreciate what views others have on the best way to go? Prefer to avoid the 150mm cavity if I can as the ground is a nightmare to dig and it would mean trimming up the trenches to widen the footings in places!

Thanks in advance

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