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Insulate garage roof from underneath
Bob watts 18/09/2026 - 8.44 AM
I have a garage roof which had sound rafters and marine ply covered in felt. I want to insulate the roof, can I do this from below?
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3 Answers
ADR Property Maintenance
Rating: 5 out of 5
Only if you want to create condensation problems
Answered18 September 2026
0
c&j developments
Rating: 4.8 out of 5
Yes use celotex or kingspan or similar 100mm preferably.cut between joists try and leave 50mm gap at top for airflow.
Answered18 September 2026
0
Brian Webster
No reviews yet
Yes, if you have a flat roof, cut the insulation in tight as possible between the joists, you may want to bang some nails in a little bit, so the insulation stays up in between the joists, if you have actually pitch rafters and your ply is fixed down to the inside of your rafters to make a floor then I'm afraid you will have to prize the plywood up and then insulate ,especially if there is a ceiling underneath already.
Answered18 September 2026
0