Warm Roof or Cavity Wall Insulation

Warm Roof or Cavity Wall Insulation

Thanks a lot for posting your videos on YouTube.

Very helpful. I currently have a flat roof extension for my bathroom and kitchen, this is how I bought the house, but it has no insulation and it leaks also.

My walls are cavity on the extension but they are not insulated, my question is, would I be better fixing the roof with a warm roof or
filling the walls with insulation? Can you tell me if I can get away with fixing or if I have to do both?

I really appreciate your time steve, im dad of 3 and everyone complains how cold the house is and im sick of huge gas bills i cant afford.

Any advice would be greatly appreciated.

Best Regards,


PS. I am thinking of doing a warm roof myself but I’m not 100% sure how the due point works, sounds tricky and not something you want to get wrong.

Hi Ben,

If I had to chose between warm roof or cavity wall insulation it would be warm roof first because at the moment the roof is the real week point.

The video you have been watching tries to point out that the warm roof should be extended down to the start of the cavity or solid wall. If you don’t do this and you then filled the cavity wall you will have a big area where the heat could get out. You are trying to be continuous with your insulation.

With regards to vapour control, the warm roof construction method is very forgiving. I’ve seen flat  roofs without any vapour control membrane working without any problems. Give it a go and get back to me if you need any more help.

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Comments (2)

  • Nader Reply

    Hi Steven,

    I currently have a flat roof over my back bedroom which is very, very cold in winter. I’ve watched your videos on warm vs cold flat roofs and I can’t tell which I have. Currently, the roof joists have no insulation between, but the roof doesn’t overhang the wall as there is a roof terrace above and so the walls all continue up a little higher than the roof to create a barrier for the terrace above. I seriously doubt there is any insulation on the floor of the terrace as it has been taken up and change so many times and is currently fibre glass which my neighbour put in not long ago. I was planning just stuff in between the joists with as much insulation as I can fit, but after watching your videos and realising that there needs to be ventilation, I am now at a loss as to what to do. there is no way I can ventilate up as in your cold roof insulation because I can’t get the neighbour to remove the roof to create a gap. Any ideas of what else I can do to make the room warmer?

    20th January 2019 at 8:09 pm
  • Katya Todorova Reply

    Hello Steven,

    Thank you for posting such a helpful videos.
    I have a quick question. Where is the best place to stop the joist in the engineering blocks (internal wall) or like it’s in the video joist continue outside and we fill it with isolation? We are doing a back extension warm roof. Thank you very much in advance.

    23rd November 2022 at 5:32 pm

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