Warm Deck Flat Roof Insulation Between Joists

If you put insulation under the decking and between the joists you lower the temperature of the decking and lower the due point thus bringing it closer to the danger point of being in the building.

Warm deck flat roof insulation between joists.

The vapour control layer is above the decking but below the insulation. Lay 12mm of plywood or osb board across the timber joists as a base for the flat roof build up. Making a warm flat roof construction but instead of putting the insulation above the structure joists as seems to be normal i propose to include the joists effectively as insulation i believe wood is quite good for that and install a proper vapour control layer underneath the joists. A warm flat roof or a built up roof bur is one where all the insulation is above the joists deck making them part of the warm fabric of the building.

The roof itself is therefore kept warm. Insulating a flat roof is relatively simple in terms of what materials you need and the steps taken to complete the job. As for insulating below the joists an insulating laminate insulation bonded to plasterboard such as celotex pl4000 or a separate rigid pir insulation board finished with a separate sheet of plasterboard can be securely fixed to the joists to provide an internal finish to the roof. A warm roof is defined as being when the all or the majority of the insulation is above the joists or deck.

Warm deck pitched roof the insulation is placed over the rafters and then a felt is placed on top. Install a vapour control layer to reduce the risk of condensation and moisture compromising the flat roof structure. How to install insulation in a flat roof with timber deck insulated above the joists. The battening and tiling is then fixed down over.

Good question theoretically when building a warm roof the vaper control layer goes on the warm side of the insulation. The insulation is immediately below the waterproofing layer. Alternatively battens can be secured to the underside of the joists and gmw fitted between these in much the same way as between the main roof joists. Warm deck insulation 1.

The thickness of insulation will vary. By majority the rule of thumb is that in a domestic house not flats approximately a third of the total thermal performance of insulation can be placed below the deck with two thirds above the deck sometimes this is called a hybrid warm roof. So a solution i would like to propose is.