Hybrid Flat Roof Insulation Between Joists

Good question theoretically when building a warm roof the vaper control layer goes on the warm side of the insulation.

Hybrid flat roof insulation between joists.

A vent baffle should be installed between the insulation and the roof decking to maintain the ventilation channel. Refurbishing an existing timber joisted flat roof which has no insulation. Consider using high density r 30 batts which are as thick as r 25 batts but fit into 2x10 framing. This is used for refurbishment e g.

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. You can also add rigid foam insulation under the rafters which adds r value and eliminates thermal bridging through wood rafters.

For many designers a perfect solution would seem to be the hybrid flat roof. It is preferred to have the bulk of the insulation between the. 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. 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.

The insulation is below the deck but above the plasterboard. If the basic warm roof construction is followed before extra insulation is installed problems can arise. A cold flat roof is one where the insulation is between or between and below the roof 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.

This is then topped up with 120mm of glass wool installed. 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. 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.