DIY Doctor

Cold Flat Roof Loft Dormer Despite Good Insulation?

Postby JuliaMH » Thu Oct 24, 2019 8:14 pm

Hi, we have a large flat roof bedroom dormer, approx 18x12ft floor shape with the large external window wall facing east and the cheeks N-S. The dormer is 20-30yrs old and had pretty much no insulation but we framed it in and added 100-120mm kingspan in all walls, sloping roof and ceiling of flat roof plus some rock wool. We also had the flat roof membrane done soon after and insulated on top too, so it has hot and cold roof insulation combined! The small loft apex where the flat meets sloping roof is also reasonably insulated. I'm not aware of any obvious roof vents directly affecting it and they'll be behind the insulation anyhow. It has 1 big radiator. To get to the point, it still feels very cold in winter when its moderately chilly, blowing a gale or it's still and bitter outside. We live right on coast and get extreme conditions. Am I being unrealistic to think it should feel cosy? Is it too big a room for 1 heat source? Would it be worth framing in the front wall again by 2-3in and adding more king Span? Are dormer rooms just rubbish? Thanks in advance
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