Warm Deck Flat Roof Insulation Between Joists

Warm deck insulation 1.

Warm deck flat roof insulation between joists.

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. A warm roof is defined as being when the all or the majority of the insulation is above the joists or deck. 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. The insulation is immediately below the waterproofing layer.

Here the roof deck is maintained at the same temperature as the internal conditions hence warm deck roof. 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. A cold flat roof is defined by insulation being installed between and if necessary underneath the timber joists. A flat roof where the insulation sits below the waterproof membrane and above the structural deck is a warm roof deck.

A warm flat roof is defined by insulation being installed on top of the roof deck. But as we are pushing head height our dormer meets the roof ridge right at ridge level so any vents and building regs seem to require a lot of them will be a little too exposed in my opinion. 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. How to install insulation in a flat roof with timber deck insulated above the joists.

No ventilation is required for these types of roofs. 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. The vapour control layer is above the decking but below the insulation. The roof itself is therefore kept warm.

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. For this reason i would prefer to have insulation between the joists as with a cold flat roof construction. The insulation can be adhered mechanically fixed or loose laid. 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.

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. 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. Warm flat roofs do not need to be ventilated as the insulation is.