Flat Roof Insulation Between And Over Joists

It is preferred to have the bulk of the insulation between the joists to reduce any risk of condensation.

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. 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. A cold deck flat roof will typically require insulation to be installed between the roof joists to comply with building regulation requirements. 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.

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. Between and under joists. Warm deck insulation 1. 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.

To build a roof joist for a flat roof you need some carpentry skills and a few basic tools. The majority of domestic cold flat roofs use insulation between and under the joists. An over and between rafter insulation solution can be a feature of a new build project. The insulation boards should be laid with the plywood face up.

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. The insulation is immediately below the waterproofing layer. Flat roof insulation always requires professional insulation and damp roofs require professional assessment before work can be carried out. 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.

The vapour control layer is above the decking but below the insulation. The roofing surface is installed over the joists while insulation is placed between them and the ceiling beneath is suspended from them. Good question theoretically when building a warm roof the vaper control layer goes on the warm side of the insulation.