Estimate for a new flat roof


Your website and videos are very good; very reassuring.
This is an old mineral felt flat roof I need an approximate quote for a cold roof repair please. Cold roof because of a window that sits on the flat roof; a warm roof is not possible.

It’s a typical Victorian north London terrace with rear addition. The flat roof is about 3m x 6m in size and situated above the rear addition, with two edges against brick walls and two open. Access is from the back garden, i.e. through the house. I can supply photos.

I will insulate from below (the ceiling is down) and would need you to do the following please:

old flet roof on a flat in Hammersmith

  • Remove two layers of mineral felt/boards (i.e. it has been re-roofed before and the original roofing boards – planks – are still in place but should be replaced)
  • I’ll supply a skip
  • Re-roof (cold) with one of the membrane options you offer.
  • Build the ventilation along the wall/parapet edge.
  • Finish detailing around all four edges including flashing, replacing fascia boards and re-pointing.
  • I’ll sort the guttering.

This is a bog-standard configuration – there must be 100,000 houses like this in north London. Are you able to give approximate quotes, for the different options, without a visit please?

Thanks in advance.

Reply to Email

Thanks for the email and the photos of the roof.

It’s a felt roof that looks quite good. I can’t see the back or the right hand side but as you state there are thousands of roofs like this, probably with a parapet along the back and a drip into the gutter, right hand side.
Yes, it’s the window that gives you the problem with turning this into a warm flat roof.
If you don’t insulate then we can cap the roof using a liquid system; basically this just goes over the existing roof. Although this is classed as a capping system, it will not trigger Part L1b and you don’t have to insulate the roof. The system I would suggest is the 3M SD650 system, as 3M give it a 25 year guarantee. Also we can possibly do the work using harnesses for health and safety.
As you are aware, if you insulate the flat roof from below, the new flat roof will have to be vented front and rear, which will definitely mean we will need scaffolding.
The option of turning this into a warm flat roof is still there; we could insulate over the felt and leave a box gutter in front of the window, we will still have to raise this area by 25mm to stop any thermal bridging.
The existing lead flashings look good so they can be re-used, although what I cannot see are the back and side details.
I would suggest that these will be OK. There will be a cost to clean the roof and carry out preparation before the roof can be laid. I do need to see the job and would like to see the some more photos, I’m assuming work can be carried out through the window?

2 comments on “Estimate for a new flat roof

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