polystyrene sheets on roof rafters.

jw 1111 · 2005-12-21T13:08:13+00:00

Hi, when we first bought out house thirteen years ago ( an end house of fourbuilt in 1936 in north London. u.k.) I went up into the roof space onewinter; and found the whole inside to be covered in a thin layer of snow.( There was quite a high wind and it had blown the snow inside between thetile gaps ).To remedy this problem i bought a roll of special roof plastic, (cannotremember the name, but it is made for this purpose and has an inbuilt latticeof nylon string for added strength ) which i laid up close to the tiles andstapled to each side of the wood rafters. This now keeps the snow out, buteverything still gets covered in a thin layer of dust and grime.We would like to further seal the roof to keep out this dust, but this doesnot have to be too elaborate, since the roof space is not a living space, butmore of a storage space. Also i have laid rock wool insulation in the floorspace so we do not need any extensive extra insulation properties on this project.what i thought would be a relatively easy option is to get some of thosebuilding sheets of white polystrene type material and cut them into stripsand nail them to the inside face of the roof rafters. they do not need to beall that strong ( but obviously must be stronger than ordinary polystyrene).would anyone know the name of such a building material or any other building material that might suit better please? But being able to slice it into strips with a knife, would obviously be a big bonus for ease of application. thanks

Dec 21, 2005 25 Replies

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Goedjn 20 years ago

Have you already stuffed the joist-bays with insulation? If not, You should investigate Homasote and similar compound building panels that combine insulation and fire-resistant surfaces in one panel. (Which would go across the joists, instead of between them.)

If you *HAVE* put the insulation in already, then sheetrock/plaster board really is your best bet. It's not as hard to work with as you apparently think it is, especially if you cut it into manageable sizes before moving it.

If you have a neurosis about the rock panels, then you could use something like Sunforger Marine Canvas (Which is available in the US in 100-yard rolls from ITEX/BANWEAR) It's fire and mildew-resistant, which doesn't mean it won't mold and burn, just that it's not quite as eager to do so as regular canvas. I suspect it's some sort of boric acid treatment. The canvas won't meet code, but it's better than either exposed insulation or stapling up old refridgerator boxes.

If you're cheap, and don't care about either meeting code or burning yourself to death, use white muslin, after giving it your own boric-acid/borac bath in your tub. or using a commercial fire-retardant on it.

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jw 1111 20 years ago

Very many thanks Goedjn. We have not yet put in the insulation between joists so will now find out about Homasote.

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jw 1111 20 years ago

Found quite a few references in a google search of Homasote in model railway enthusiasists newsgroups who use it as a 'base' board for train tracks in outside garden sheds. There is a lot of talk about it being prone to movement in changing humidity and also it can sag if joists are more than 16 inches apart. Guess this might mean I have to keep looking. Or any further suggestions please?

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Goedjn 20 years ago

Homasote is a company that makes a number of products, mostly out of recycled cellulose. What you're probably reading about is their grey fiberboard, which is used under floors and behind sheetrock for insulation and sound-control. They've got a whole catalog's worth of stuff at

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SOMETHING in there ought to work. Failing that, you might look at structural insulated panels (SIP) which are a sandwich of fiber-board and foam insulation. As much of a pain to work with as sheetrock, but again, insulating and surface at the same time.

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jw 1111 20 years ago

Many thanks and thanks to all. I have found some 'kingspan thermopitch' panels. (foam between two sheets of aluminium foil) and am now in the process of putting them up.

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