Solid wall internal insulation - risky long term??

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10 Sep 2012
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London
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United Kingdom
Hi,

I am doing a full renovation of my 1890 solid wall victorian terrace, and before replastering would like to take the opportunity to insulate the external walls.

so far so good.

My builder has recommended rendering these wall with a waterproofing additive (sika) first, then attaching laminate insulated plasterboard (e.g. celotex pl4000) to the render using dot and dab adhesive.

building regs suggest that i should be using 50mm of insulation under 12.5mm plasterboard.

having done a bit of reading, i'm concerned about condensation on the wall behind the insulation, and particularly on the ends of the first floor joists and the bressumer beam which they rest on. as I will be insulating the walls on the first floor and the ground floor, but with a gap where the floor itself is, there is (apparently) a risk that moisture from within the building could attack the timber here.

All the documents that i have read state that the insulation should be fitted with great care, and that the quality of the work is essential to stop gaps in the built in vcl, but if there is a gap in the insulation the height of the first floor joists and running the whole width of the building, it sounds like its guaranteed to fail.

does anyone have any long term experience with this?

At the moment I am almost convinced to live in a colder house rather than risk having my floors rot underneath me!

Any advice welcomed.

thanks,

j[/b]
 
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