Insulation

Insulating uPVC panel under window using timber frame

Anonymous user 3 March 2024 - 3.41 PM

I have single thickness uPVC panel under the front window down to the ground, as part of the external wall. It's 3m long and 50cms high and set into the same frame as the window. I want to insulate this area by building a timber frame on the inside of the uPVC panel, filling it with insulation board, then plasterboard with a timber window sill on top. This would fill in the window reveal in the living room and be flush with the walls on either side. I have read that insulation needs a 5cm air gap on the 'cold' side. Does this apply here? The outer skin will be the existing uPVC panel, which has a frame and two centre panels set 2.5 cms in from the frame. So could the air gap could be 5cms over most of the panel and 2.5 cms around the frame? Also I've read that a vapour barrier is needed on the 'warm' side. I guess this applies here? What would be the best way to provide insulation, vapour barrier if needed, and plasterboard surface? Any advice welcome. Thanks.

Louis Carlsen Build and Renovation LTD

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Windsor

Hi, The make up of your uPVC panel is a plastic vapour proof face, 3mm mdf around 20mm of insulation and another vapour proof face. Knowing this I would build your stud work to meet your requirements around 2.5 or so off the frame, this is really only to stop cold bridging, then fill with a wool insulation such as ego wool or rockwool then board and skim In this situation I would not add a vapour barrier, in some situations they are vital and others can stop airflow and course problems I wish you luck with your project Lee, Louis Carlsen build and renovation

Answered24 January 2022

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