How To Insulate A Flat Roof Externally

It should be of the maximum available thickness.

How to insulate a flat roof externally.

Then install r 30 fiberglass batts between the rafters. You would only do this however if replacing the roof covering on top and you have the height above the roof to do this. To achieve this add 100 to 160mm of insulation above the structural deck dependant upon insulant conductivity. Insulation material is placed on top of the roof rather than in between the ceiling and the decking.

The typical u value of an existing uninsulated flat roof is 1 5w m2k. Creating a void between the old ceiling and new is better but ideally you need to eventually consider insulating the top of the concrete roof with solid insulation and a better covering grp or epdm. The target should be to achieve a u value of 0 25w m2k or better. With a warm roof the usual process is to split the insulation into two layers.

Insulation is placed in between the joists underneath the roof surface above. The correct method for a flat roof is under the current regulations to have a warm roof. 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. Ventilation is necessary to allow moisture accumulated inside to escape.

When a homeowner really needs to cut down on costs some contractors may suggest the following. Proper ventilation in flat roofs. It should be installed on tapered 2x furring strips in order to slope the surface of the roof to drains. 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.

Flat concrete roofs are generally not ventilated since the ceiling internally is generally a plaster and skim coat directly to the underside of the cold concrete. Add an additional layer of osb over the sheathing.