Flat Roof Insulation Between And Over Joists

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.

Flat roof insulation between and over joists.

Constructing a warm roof on a new extension with parapet walls i will have surplus amounts of insulation left over and am considering adding this insulation to the underside between the joists to double up the insulation would this install have any negatives. The insulation is immediately below the waterproofing layer. This method of insulation can also be used to upgrade the thermal performance of an existing roof without affecting the waterproofing system. 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.

Bs 5250 2011 the british standard for the control of condensation in buildings does not recommend installing insulation between timber joists as well as above the deck. Where insulation depth is restricted by the flat roof construction it may be necessary to install the roof insulation between and below the joists to create a cold deck structure. Lay mineral wool between the joists and then fit rigid insulation boards across the joists with floorboards on top. You could even buy insulation and floor boards that are already bonded together which makes the job much faster and easier.

Can insulation be placed between and over flat roof joists. The majority of domestic cold flat roofs use insulation between and under the joists. Learn more about warm roof cold roof construction. To increase the thickness of your roof insulation layer you can.

Flat roof insulation between and under joists a cold deck flat roof will typically require insulation to be installed between the roof joists to comply with building regulation requirements. To protect the roof from the potential of condensation occurring unseen within the construction it s important to remember that the layer of insulation installed over the rafters should as general rule be double the thickness of the insulation layer between the rafters.