How To Insulate A Flat Roof Externally

The correct method for a flat roof is under the current regulations to have a warm roof.

How to insulate a flat roof externally. You would only do this however if replacing the roof covering on top and you have the height above the roof to do this. It should be installed on tapered 2x furring strips in order to slope the surface of the roof to drains. Ventilation is necessary to allow moisture accumulated inside to escape. It also lets hot air escape in the summer.

With a warm roof the usual process is to split the insulation into two layers. 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. Insulation material is placed on top of the roof rather than in between the ceiling and the decking. 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.

To achieve this add 100 to 160mm of insulation above the structural deck dependant upon insulant conductivity. It should be of the maximum available thickness. Insulation is placed in between the joists underneath the roof surface above. Add an additional layer of osb over the sheathing.

The material that works best depends largely upon preference in a given situation. Proper ventilation in flat roofs. 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. Like other roofs insulating a flat one requires ample ventilation a vapor barrier and sealed bypasses.

Then install r 30 fiberglass batts between the rafters. When a homeowner really needs to cut down on costs some contractors may suggest the following.