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Where to put insulation in the loft?


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Hi Everybody ? 

 

Got a loft with the central part boarded out upto the uprights of the ashlaring wall.
Above this area the rafters look like they've been stuffed tight with glass wool,
then a vapour barrier over the lot followed by some wooden cladding.

Beyond the ashlaring and to the eaves, the ceiling has a hefty layer of glass wool
both between and on top of the beams. The rafters above this has NO insulation. 

I'm going to remove all the cladding and glass wool on the main ceiling and add
PIR instead to ensure a gap between felt and board > plasterboard etc.

Then I was going to just put PIR between the uprights of the ashlaring wall and again
plasterboard it over, but what of the rafters upto the eves with no insulation?

So my question is, instead of insulating the part surely it be better to use that same insulation
over the entire roof instead? 

Am I missing something here? 

Ed 

 

Edited by Ed21
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It's been awhile since I converted my loft, but Im sure  a portion behind the walls remains relatively un-insulated;

 

So the floor was insulated all the way to the eaves tray vents,(the rafters had an un insulated portion of about a foot - where the timbers that bolted rafters to ceiling joists are) Then the dwarf wall was insulated vertically and between/below the rafters upwards untill the rafter tie above the ceiling. 

So there's a triangle at the top uninsulated and a triangle at bottom. 

 

They 're connected by a 50mm airgap, with lap vents inside and a ridge vent at the top. 

 

It's essentially an insulated cube inside a tringle. 

My felt was non permeable and there is a continuous airtight layer on the inner face of the insulation. 

 

You could insulate the entire triangle of the roof and not bother with the walls at all as long as its ventilation is sufficient. 

Edited by syne
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