1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

New cold flat roof ventilation advice

Discussion in 'Roofing and Guttering' started by Coyney, 29 Oct 2016.

  1. Coyney

    Coyney

    Joined:
    29 Oct 2016
    Messages:
    4
    Thanks Received:
    0
    Country:
    United Kingdom
    Hi all,

    I'm new to the forum and purchased a 1950s detached house about 6 months ago.

    The existing flat roof of a two storey extension was sagging badly and had damp spots. A relative of mine is a roofer and replaced the 5m x 3m area with new joists, plywood and several different layers of torch on felt.

    Upon completion I decided to look at the different options of insulation and noticed that this was deemed cold roof construction without ventilation. I can generally put my hand to most tasks but have never been involved in flat roof construction.

    The 5inch joists are exposed to the underside and I haven't yet insulated it so I can still acces the underside.

    Is there a way I can ventilate it as I don't want to rip the roof back up? Can vents be added to the fascia boards? I was going to buy 75mm celotex to ensure 50mm clearance but am now worried about potential condensation, after reading about its construction online.

    Thanks in advance,
     
  2. Sponsored Links
  3. freddiemercurystwin

    freddiemercurystwin

    Joined:
    21 Jan 2007
    Messages:
    18,845
    Thanks Received:
    2,088
    Location:
    Devon
    Country:
    United Kingdom
    WTF? You had a 'roofer' do this for you and you're only thinking about ventilation and insulation after its been built?

    Anyway, got some photos, which way do the joists run, how is the fascia suspended?
     
  4. Coyney

    Coyney

    Joined:
    29 Oct 2016
    Messages:
    4
    Thanks Received:
    0
    Country:
    United Kingdom
    Thanks for the response. I know, it's frustrating, but I've never had a flat roof and didn't realise until I researched insulation.

    The joist run from the main roof outwards. The first photo shows them running into the wall furthest away from the house.

    image.jpg

    The following photo shows the joists running up to a wooden fascia board.

    image.jpg

    This is the end where the joists butt up to the blocks of the main house. Above these there is some timber that I may be able to drill through to get to the main roof space.

    image.jpg

    This is the view from the main house showing the fascia board.

    image.jpg

    Any advice on venting this and also on the insulation will be much appreciated.

    Thanks.
     
  5. dom_k

    dom_k

    Joined:
    7 Aug 2016
    Messages:
    35
    Thanks Received:
    10
    Country:
    United Kingdom
    I'd put 75mm between and 50mm under joists. Not quite enough to meet current building regs though. Re the vents an over fascia vent would have been good. Do you have a soffit on the gutter edge? At the other end venting into roofspace may be your only option.
    I'm guessing the roof may have been shot due to decayed timber from lack of ventilation?
     
    • Thanks Thanks x 1
  6. Coyney

    Coyney

    Joined:
    29 Oct 2016
    Messages:
    4
    Thanks Received:
    0
    Country:
    United Kingdom
    Thanks for the advice regarding the insulation. Would you also use 12mm foil backed plasterboard over it?

    Unfortunately there is no soffit as the fascia is almost flush with the brickwork. Can I fit vents directly on the fascia? Would you fit them between every joist or is every other one enough? What vents do you recommend? I'll drill holes and vent into the roof space as suggested.

    The old roof was vented with 2 roof vents. In the centre there was about 5 layers of felt to try and patch up a leak. Over time I think the weight of a puddle caused it to sag but it continued to leak through on to the timbers.

    Thanks!
     
  7. Coyney

    Coyney

    Joined:
    29 Oct 2016
    Messages:
    4
    Thanks Received:
    0
    Country:
    United Kingdom
    Please can someone advise on this? I'm hoping to somehow add some venting and insulation this weekend?

    Thanks.
     
  8. DIYnot Local

    DIYnot Local

    Joined:
    3 Sep 2019
    Country:
    United Kingdom

    If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

    Select the supplier or trade you require, enter your location to begin your search.


    Are you a trade or supplier? You can create your listing free at DIYnot Local

     
  9. Sponsored Links
Loading...

Share This Page