Advice - Flat roof insulation

Discussion in 'Builders' Talk' started by Greenspace, Nov 14, 2017.

  1. Greenspace

    Greenspace New Member

    We want to insulate our flat roof (looks like cold flat roof) in our 1960s renovation house. As you can see it currently has 1cm of fibreglass above joists in most places.
    I'm aware we should have 50mm gap above new insulation for ventilation, and the joists are 170mm in height so up to 120mm to install insulation between the joists. We have lots of cables and some pipes running through the joists so some areas will be hard to install some or any installation board.

    1. Is it worth installing insulation board where we can and then using something else where all the cables and pipes are, or is that a waste of time?
    2. The felt roof above is coming towards the end of its life (already has some leaks to be fixed) would it be cost effective to convert it to a warm roof?
    3. Is the thin layer of fibreglass going to cause us any problems with condensation if we install extra above the plasterboard, Do you think the current insulation actually does anything?
    4. Should we be looking at anything else?

    Thanks in advance

    Attached Files:

  2. KIAB

    KIAB Well-Known Member

    To meet the current insulation u values, then a warm roof is the only sensible option,(cold roof so old fashion & a lot of hassle with ventilation),use OSB3 18mm with 100m insulation ideally, & grp covering.

    GRP should easily last 40 years or so.
    Last edited: Nov 14, 2017
    Greenspace likes this.

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