Warm Flat Roof Insulation Between Joists

Good question theoretically when building a warm roof the vaper control layer goes on the warm side of the insulation.

Warm flat roof insulation between joists. A cold deck flat roof will typically require insulation to be installed between the roof joists to comply with building regulation requirements. Insulation material is placed on top of the roof rather than in between the ceiling and the decking. The insulation boards should be laid with the plywood face up. There are two main types of flat roof that require different approaches to installation.

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. So a solution i would like to propose is. 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. Set the quinn therm qrfr ply insulation boards onto a wide 30mm bead of vapour resistant sealant applied to the upper surface of all the joists and cross noggins.

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. In creating the cold flat roof air is allowed to circulate freely between the joists and there is no insulation. Here the roof deck is maintained at the same temperature as the internal conditions hence warm deck roof. The vapour control layer is above the decking but below the insulation.

The insulation is immediately below the waterproofing layer. Between and under joists. A warm flat roof is defined by insulation being installed on top of the roof deck. A warm roof is defined as being when the all or the majority of the insulation is above the joists or deck.

How to install insulation in a flat roof with timber deck insulated above the joists. A cold flat roof is defined by insulation being installed between and if necessary underneath the timber joists. The roof itself is therefore kept warm. Insulation is placed in between the joists underneath the roof surface above.

A warm deck roof is where the insulation is placed on top of the rafters joists and the roof covering is then placed over the insulation. Unless the joists are exceptionally deep there is also likely to be a requirement to install insulation to the underside of the joists as the upper 50mm of joist space is usually required to be left clear for ventilation purposes.