Warm Deck Flat Roof Insulation Between Joists

A cold flat roof is defined by insulation being installed between and if necessary underneath the timber joists.

Warm deck flat roof insulation between joists.

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. Cold deck roof a cold deck roof is where the insulation is placed between the joists rafters or in between the ceiling joists in the case of a pitch roof. Warm flat roofs do not need to be ventilated as the insulation is. A warm roof is defined as being when the all or the majority of the insulation is above the joists or deck.

Warm deck insulation 1. Cold flat roofs are typically avoided as you d need to install ventilation which can prove problematic for many reasons relating to space labour costs etc. Good question theoretically when building a warm roof the vaper control layer goes on the warm side of the insulation. 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.

A flat roof where the insulation sits below the waterproof membrane and above the structural deck is a warm roof deck. 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. Here the roof deck is maintained at the. Saint gobain insulation uk manufacture and supply glass mineral wool slabs and rolls along with rigid polyisocyanurate pir boards that can be considered suitable for a wide range of applications across flat roofs whether you re looking to insulate at joist level or above the roof deck in your flat roof construction.

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. Here the roof deck is maintained at the same temperature as the internal conditions hence warm deck roof. The insulation is immediately below the waterproofing layer. The vapour control layer is above the decking but below the insulation.

The underside of the rafters in this case will need to be finished with a suitable vapour control layer vcl and plasterboard to provide a suitable internal finish to the roof. No ventilation is required for these types of roofs. The roof itself is therefore kept warm. The insulation can be adhered mechanically fixed or loose laid.

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.