How To Insulate A Flat Roof Extension

To achieve this add 100 to 160mm of insulation above the structural deck dependant upon insulant conductivity.

How to insulate a flat roof extension.

If insulation is being added to an older building then it is common practice for the ceiling itself to be taken down. The existing ceiling is sound but provides no insulation. The target should be to achieve a u value of 0 25w m2k or better. The insulation material for a warm flat roof should.

A sheet vapour barrier fitted to the inside of the rafters not required if the insulated plasterboard incorporates a vapour barrier. The typical u value of an existing uninsulated flat roof is 1 5w m2k. These are can be supplied with rebated edges which interlock reducing the risk of uplift. This will enable the airflow to circulate freely.

I ve built a timber frame to support a new plasterboard ceiling below the existing one. The correct method for a flat roof is under the current regulations to have a warm roof. With a warm roof the usual process is to split the insulation into two layers. Then install r 30 fiberglass batts between the rafters.

Insulation in a warm roof. Add an additional layer of osb over the sheathing. There is only a small gap between this ceiling and a concrete roof cold roof felt covered. If 180mm is to be installed then 100mm board might be introduced between the rafters there has to be a minimum 25mm air gap between the insulation and the underside of the tiles or slates with an 80mm board running across the rafters.

It should be installed on tapered 2x furring strips in order to slope the surface of the roof to drains. When a homeowner really needs to cut down on costs some contractors may suggest the following. Sheet insulation fitted between the rafters the thicker the better but the size of rafter may limit the thickness possible once an allowance has been made for the required 50mm 2 inch air gap. In a nutshell you would sandwich 130mm of solid insulation between two decks allowing to place a vapour barrier on top of the first deck.

The insulation material is placed between the supporting joists leaving a gap of 50 60mm between the roof and insulation. The insulation for a warm roof will usually be boards of extruded polystyrene or rigid compressed boards of glass fibre or rock fibre.