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Roofing

Warm or cold roof, with rendered walls?

Anonymous user 28/02/2024 - 4.04 PM

Hi, we are currently having a single story rear extension, and we are having a flat roof with the external walls rendered. My builder was going to do a standard cold roof - insulated between the rafters. The building inspector has said that due to the walls being rendered, that we need to do the roof as a warm roof - so the insulation now sits on top, so that there is sufficient ventilation. The problem we have is that this space was to be used so we could have a parapet with a side draining system with no guttering. But If we have to now have this specific insulation, this takes up most of the space that we had - and we can’t go any higher. Does anyone know if this is correct and we have to do the roof in this way? Or are there any other solutions? Thanks I’m advance, as I’m getting very stressed now!

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3 Answers

Anonymous user

Ive been in simiar situations.. in the past ive got round it by screwing 2×2's on top of the existing rafters and edges to raise them so there is a sufficent 2inch air flow gap . Have a word with your roofer and see what he thinks raising it 2 inches then u can have the insulation inbetween and still have your air gap.. im guessing at the moment if you put it straight in to rafters its going to be flush with the top of then touching the underneath of the boards which will cause condensation damp etc.. so 2inch by 2inch beams along the existing rafters to get a ventilation gap.. i havent seen your roof so its hard to say but it worked for me on a slate roof joined to flat because we just cut the bottom row of slates down when the roof was raised had to strip out slates and out back higher.. hope i helped somewhat

Answered16 June 2022

Diamond Fibreglass Ltd

Rating: 5 out of 5

Kidderminster

100% always go "Warm" roof, you can still have your roof with a hidden valley (i think this is what you want) just increase the furring heights so you can finish a foot from the end on the roof with about 2" left in heighton the furrings then start the diminishing strips at 1.5" or lower if it allows in your valley fall. You can also fit 100mm PIR to the valley and 120mm PIR to the main roof this will give you height to play with in the valley

Answered26 June 2022

Roofing Angels

Rating: 5 out of 5

Walthamstow, London

We agree with Diamond Fibreglass, a warm roof is always the way to go and if the building inspector has recommended this, then its need must meet building regulations.

Answered18 August 2022