Warm 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.

Warm roof insulation between joists.

How to install insulation in a flat roof with timber deck insulated above the joists. The flexible nature of gmw means that the roll or batts can be accurately cut and friction fitted between the rafters thereby minimising air gaps and maximising thermal performance. The insulation can be adhered mechanically fixed or loose laid. 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.

The insulation boards should be laid with the plywood face up. 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. This type of detail gets accepted on garage conversions and the like but they are conversions not new build where there is little scope to achieve a proper warm roof as the existing roof finish is being retained. Reducing the risk of harmful condensation.

Isover glass mineral wool gmw is another option for the between rafter insulation as a roll or batt. The insulation is immediately below the waterproofing layer. 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 180mm is to be installed then 100mm board might be introduced between the rafters there has to be a minimum 25mm air gap between the insulation and the underside of the tiles or slates with an 80mm board running across the rafters.

The vapour control layer is above the decking but below the insulation. If its in between and no vents its a hybrid and may or may not be accepted by building control. 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. Warm deck insulation 1.

The roof itself is therefore kept warm. Good question theoretically when building a warm roof the vaper control layer goes on the warm side of the insulation. 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.

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. Its only a warm roof if there is insulation above the joists.