Hi, my first post here.
We are just having a new boiler and cylinder installed in the loft so I am taking this opportunity to make it a more usable storage space.
The first thing I need to consider is that the loft is a 1930's roof that has no lining so it gets dirty. So I figured I could install Kingspan / Celotex boards between the rafters. This should serve two purposes, in improving insulation for the house and stop the dirt from covering stuff that is stored in the loft.
The trouble is the rafters are only 3" (76mm) and I would like to put the thickest grade of insulation board possible between the rafters. I have spent quite a while reading through as many posts as I can find to try and find how much of a gap is required.
So far I have found that lined with non breathable membrane such as tar paper should be 50mm gap at the back where as a breathable membrane would be OK at 25mm. But what I can't find is what gap should be left when there is no membrane.
I don't really want to make the rafters deeper if possible by adding for example an extra 50mm baton on them as that would add more weight to the roof that already will have extra weight on it with a solar collector.
The roof is in good condition with tiles hung rather than nailed slates so it doesn't really need re-roofing.
Appreciate any advice anyone can offer.
We are just having a new boiler and cylinder installed in the loft so I am taking this opportunity to make it a more usable storage space.
The first thing I need to consider is that the loft is a 1930's roof that has no lining so it gets dirty. So I figured I could install Kingspan / Celotex boards between the rafters. This should serve two purposes, in improving insulation for the house and stop the dirt from covering stuff that is stored in the loft.
The trouble is the rafters are only 3" (76mm) and I would like to put the thickest grade of insulation board possible between the rafters. I have spent quite a while reading through as many posts as I can find to try and find how much of a gap is required.
So far I have found that lined with non breathable membrane such as tar paper should be 50mm gap at the back where as a breathable membrane would be OK at 25mm. But what I can't find is what gap should be left when there is no membrane.
I don't really want to make the rafters deeper if possible by adding for example an extra 50mm baton on them as that would add more weight to the roof that already will have extra weight on it with a solar collector.
The roof is in good condition with tiles hung rather than nailed slates so it doesn't really need re-roofing.
Appreciate any advice anyone can offer.
