Warm Roof & Cold Roof Venting

Warm Roof & Cold Roof Venting

Warm Roof & Cold Roof Venting

Roof access is easy, stable and safe. It takes a few minutes to rig the ladder, but this is not feasible if it’s raining at the time because rain would enter the bedroom through the french doors. Front of house scaffolding will be required for the job.

I had the conversion done 20 years ago. The flat roof has a very shallow slope and consists of joists, surmounted by furring pieces, transverse spacing battens for ventilation, ply deck with mushroom ventilators, and multiple felt layers.

It is also penetrated by a soil pipe near the condensing boiler vent. The ply deck appears to be in sound condition but blackened, presumably by condensation.  There is existing 3″ fibre glass blanket insulation.  Patched last December at every vaguely suspect spot after a leak from a significant split, and currently leak free.

I’d like your opinion on the best way forward for a long-term fix.


Warm Roof & Cold Roof Venting

You’ve got the height to do a warm roof; we will need to play with the front ridge tiles, but I cannot see a problem.

You have lower vents to the front elevation roof but no upper vents! The vents on the roof probably only vent the flat roof; I can’t see how they would have achieved through ventilation from the vents at the bottom, all the way to the flat roof, as there will be a huge steel or some large timbers going across under the ridge tile. Investigations will need to be carried out to clarify what exactly is going on.

As you have a cold roof at the moment, we must look to see if keeping the roof as a cold roof is cheaper. You could certainly overlay the existing roof coverings with ease, and give yourself a new roof.

However you then need to look into how you will upgrade the thermal qualities of the roof, and the only feasible way of doing this would be to:

  • Remove the internal ceiling.
  • Remove the old insulation and replace with new.
  • Then, before replacing the ceiling, tack over the joist with a continuous sheet of insulation, probably 50mm thick to achieve the correct U value for building control.
  • Then replace the ceilings and re-decorate.

It’s pretty obvious that to form a new cold roof to the correct standards would be much more expensive, and rather invasive to the rooms below. So, going back to the warm roof option, further investigations into the existing ventilation will need to be undertaken, and any cross ventilation terminated; introducing more tile vents to the pitch roof would continue it’s through ventilation.

The build up of the warm roof will be:

  • Glue down the insulation over old roof .
  • Supply and lay new EPDM rubber over the new warm roof insulation.
  • Hope this helps get back to me if yo need any more information.
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Comments (1)

  • Jonathan Hyde Reply

    Hi. Just about to fix our warm roof construction down. I’m aware of the advantages and disadvantages of warm and cold roof systems but I’m unsure how our soil pipe is going to affect condensation in the roof. Our soul pipe is going to be piercing the warm roof structure and I’m worried about condensation forming as it passes through the warm roof insulation and the vapour control layer into the warmer moist air of the interior.
    Is the solution to vent that area, or to extra insulate around the soil pipe? Or to vapour barrier off the whole soil pipe as it comes through from the house into the warm roof construction?

    20th August 2018 at 6:14 pm

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