Warm Flat Roof Insulation Between Joists

The insulation boards should be laid with the plywood face up.

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. The vapour control layer is above the decking but below the insulation. Between and under joists. 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.

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. If insulation is being added to an older building then it is common practice for the ceiling itself to be taken down. 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. Here the roof deck is maintained at the same temperature as the internal conditions hence warm deck roof.

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 insulation material is placed between the supporting joists leaving a gap of 50 60mm between the roof and insulation. Warm deck insulation 1. Here the roof deck is maintained at the same temperature as the external conditions hence cold deck roof.

In the warm flat roof construction there is insulation packed into every possible space where air can flow. Good question theoretically when building a warm roof the vaper control layer goes on the warm side of the insulation. A warm flat roof is defined by insulation being installed on top of the roof deck. So a solution i would like to propose is.

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. 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.