Hybrid Flat Roof Insulation Between Joists

If the basic warm roof construction is followed before extra insulation is installed problems can arise.

Hybrid flat roof insulation between joists. When issues like those above occur it s not surprising that people look at the space between the joists and wonder if they can use it for more insulation. A thinner insulation over the top of the roof gives the benefit of a warm design no ventilation while accommodating the majority of the insulation between the joists keeps the profile as thin as possible. It is preferred to have the bulk of the insulation between the. 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.

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. Imagine a flat roof constructed on timber deck and joists. The insulation is below the deck but above the plasterboard. This is then topped up with 120mm of glass wool installed.

The majority of domestic cold flat roofs use insulation between and under the joists. Our final example of this block is a hybrid flat roof insulation solution is a highly cost effective solution where larger timbers 150mm have already been installed the solution starts off with our next gen sf19 superfoil insulation installed across the top of your joists with firings overs the top to provide the necessary drop. 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. The latter places insulation on top of the roof deck while the former puts it below typically between or underneath the roof joists.

This is used for refurbishment e g. A vent baffle should be installed between the insulation and the roof decking to maintain the ventilation channel. You can also add rigid foam insulation under the rafters which adds r value and eliminates thermal bridging through wood rafters. A cold flat roof is one where the insulation is between or between and below the roof joists.

A third option that is perhaps less well known is the hybrid roof which places insulation above and below the deck and therefore below the vapour control layer vcl with no allowance for ventilation. Refurbishing an existing timber joisted flat roof which has no insulation. The rule of thumb for foil faced boards like thermapitch tp10 or kooltherm k7 in this scenario is that you can have no more insulation under the joists than you have between the joists.