Loft insulation with 7cm joists

16 Jan 2008
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United Kingdom
Hi All,

I'm looking to sort out the insulation in my loft. One half of the loft is part boarded currently, the other half has 100mm of insulation laid on top of the joists with scraps in between.

The joists are only 7cm deep - at least until you hit the top of the lath and plaster ceilings. On the non-boarded side this shouldn't matter, I was planning on laying more insulation on top of the existing stuff to make it up to 270mm.

But on the part boarded side, things are tricky. I can take up the current boards, and lay extra joists at 90 degrees - but is it feasible to increase the joists by 200mm to give space to lay the insulation rolls?

Or there's the Knauf Loft Boards which can be laid on top of existing boards, but they're working out at ~500 quid for a 6m x 4m area.

Anyone got any general advice or options which I'm not aware of? Any help from people with similar problems would be appreciated.


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you could use a PU insulation board such as celotex laid over your joists,you would need amuch thinner board and you could refix your boards back to the joists directly through them without the need for any extra timbers 100mm over your existing insulation would probably see you close.

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