Insulation in loft storage room

22 Apr 2014
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United Kingdom
The house I just bought has had part of the loft converted to use as a storage room (not a heating living space). It has a staircase leading up and the roof has been boarded out with plasterboard & skimmed. Under the plasterboard is some mineral wool insulation. There is also a little insulation (about 75mm) under the floorboards up there, between joists.

I plan to remove the floorboards and fill the joists with 200mm of insulation, to help keep the house below warm. The bit I need help with is the roof and the rafters. There has been no air gap left between the current insulation between the rafters (about 75mm of mineral wool). I was planning on removing all of the plasterboarding, removing current rafter insulation and replacing it, leaving a 50mm air gap between insulation and the roof felt. Then re-boarding & re-skimming it.

First question is.. is this additional insulation pointless? It's not a heated living space, so is there any point to this additional insulation in the rafters (I was going to put in 75mm of insulation)?

second question.. I was going to use the Jablite polystyrene insulation boards from B&Q, 25mm thick between rafters then 50mm thick over the rafters, then board it out with fire resistant plaster board (ensuring no insulation comes into contact with wiring etc). is this safe?

I've attached a couple of photos of part of the loft space (please excuse the mess, lots of junk left behnd by previous owners). The cavity below the floorboards is 200mm deep. Rafters are 70mm deep.



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No point insulating it if no heat will ever get to it.....

It may keep it cool in the summer a bit, but probably pointless....

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