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Overboard plasterboard with thermal plasterboardboard

Postby SusieRose » Mon Aug 01, 2022 7:03 am

I live in a "Cornish house" The House used to be PC concrete on the ground level . This was changed to Cavity( brick & thermalite) in the '80s. The 2nd floor is tiled with an air cap that runs all around the house.(mansard roof) I have learned the top is insulated with polystyrene & plasterboard on one side, but the other side is just Plasterboard!!!. Can I overboard with thermal plasterboard or do I have to rip all of the plasterboards off ( I hope not) to achieve some type of thermal insulation for the house?
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Postby stoneyboy » Fri Aug 05, 2022 9:32 pm

Hi susierose,
The issue is whether condensation will form in the original plasterboard if you leave it in place. You could minimise this by fitting a damp proof membrane (DPM). The construction would then be: old plasterboard; expanded polystyrene; DPM; new plasterboard.
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Postby SusieRose » Sun Aug 07, 2022 9:33 am

Thank you for the reply, it has helped me a lot. I did wonder about the condensation due to the cold air travelling inside and up to the loft area.
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Postby stoneyboy » Sun Aug 07, 2022 9:35 pm

Hi susierose,
You need the air movement in the gap all round you house to remove condensation.
Regards S
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Postby SusieRose » Mon Aug 15, 2022 9:51 am

Why is PIR board not useful instance, it has the foil protection to help with condensation.
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Postby stoneyboy » Mon Aug 15, 2022 9:30 pm

Hi susierose,
Foil faced PIR board will work but it will cost you £10 extra per 1.2m x 2.4m sheet.
Regards S
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Postby SusieRose » Tue Aug 16, 2022 4:39 pm

Thank you for your expertise. I will follow your first reply to try and get some form of thermal insulation using the products you have stated. Thank you very much.
SusieRose
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