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blowin · Posted: Thu Apr 09, 2009 12:02 am Post subject: DIY ceiling insulation

We have a flat roofed extension and only recently discovered that the room costs so much to heat because the cheapscate who built it failed to put any insulation above it . It would have been a nightmare and/or prohibitively expensive to get fibreglass or that granular stuff into the void and , anyway , the roof leaks so whatever we used would have to be non-absorbent Evil or Very Mad

. So

I had the seemingly brilliant idea of putting battons on the underside of the ceiling then slotting sheets of expanded polystyrene between them . ( The stuff which is normally used for underfloor insulation ) . Easy to handle , hardly any weight to support and not too expensive Very Happy

.
The existing wiring was a bit suspect and I wanted to add a few more lights anyway so I just put new wiring up between the ceiling and the insulation . Very easy . Then held everything together and finished it off with tongue & groove boards to give a nice wooded ceiling .
Happy days Very Happy

.............. Until a builder friend told me that the whole lot would have to be taken down again within 7 years ( max ) Shocked

...
.... because that kind of insulating material has a chemical reaction with the plastic coating on electrical wiring ! The latter would gradually melt and eventually leave naked wire exposed with potentially disasterous consequences .
Very few people seem to know that but it is apparently at least half true . That is to say that the coating on the cable definitely degrades but a guy who has seen this more than once ( usually behind stud walls ) says that the coating goes very brittle , rather than melts . I guess that is marginally better unless or until you want to change a light fitting or similar ( because the coating would flake off the cable while you were doing so ) . Come to think of it I have seen it myself in another part of the house , which was insulated with similar but thinner sheeting a good few years ago . I had assumed that the cause in that case was overheating by the lightbulb in an enclosed globe . Perhaps it was but that ^ might not have been such a good idea after all . Feck it !