Flat Roof Insulation Between And Over Joists

The insulation boards should be laid with the plywood face up.

Flat roof insulation between and over joists.

An over and between rafter insulation solution can be a feature of a new build project. 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. The roofing surface is installed over the joists while insulation is placed between them and the ceiling beneath is suspended from them. The majority of domestic cold flat roofs use insulation between and under the joists.

Can insulation be placed between and over flat roof joists. The vapour control layer is above the decking but below the insulation. To build a roof joist for a flat roof you need some carpentry skills and a few basic tools. Flat roof insulation always requires professional insulation and damp roofs require professional assessment before work can be carried out.

Unless the joists are exceptionally deep there is also likely to be a requirement to install insulation to the underside of the joists as the upper 50mm of joist space is usually required to be left clear for ventilation purposes. Pipes water tank and loft hatch insulating between the joists of your loft will keep your house warmer but make the roof space above colder. A cold deck flat roof will typically require insulation to be installed between the roof joists to comply with building regulation requirements. The insulation is immediately below the waterproofing layer.

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. 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. It is preferred to have the bulk of the insulation between the joists to reduce any risk of condensation. Between and under 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. 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. Good question theoretically when building a warm roof the vaper control layer goes on the warm side of the insulation.