Insulating A Flat Roof From Outside

Fur down the rafters for more r value after evaluation air seal insulate and control the vapor diffusion.

Insulating a flat roof from outside.

Like other roofs insulating a flat one requires ample ventilation a vapor barrier and sealed bypasses. To produce a hot roof rigid insulation is fitted outside above the weatherproofing. The insulation material is placed between the supporting joists leaving a gap of 50 60mm between the roof and insulation. With this kind of roof the insulation follows the slope of the roof.

While insulation for a flat roof is expensive and can account for as much as 25 of the total installation cost there are a number of important benefits to having it in place. Why its important to insulate your flat roof. The correct method for a flat roof is under the current regulations to have a warm roof. Materials used to make insulation in these three types include mineral wool fiberglass cellulose fiber vermiculite styrofoam polystyrene and polyurethane.

A roof over a vented unconditioned attic does not need to include any insulation. Rigid foam panels are available in thickness. Use rigid foam insulation panels on your flat roof before applying the final roof covering or inside the house before adding sheetrock or paneling. You would only do this however if replacing the roof covering on top and you have the height above the roof to do this.

This is then covered with a further weatherproofing layer. Many properties use this option as there are no additional costs for scaffolding or organising how to gain safe access to the roof exterior. Insulated roof assemblies can be vented or unvented. They lose loads of heat and are prone to leaking causing the materials to deteriorate.

The material that works best depends largely upon preference in a given situation. Or insulate partially on the exterior side of the roof sheathing with an air control layer insulate in the rafters bays control the vapor diffusion and re work the fascia soffit etc. However most cathedral ceilings and low slope flat roofs are insulated roof assemblies. 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.

Cold roof a very bad idea. Not cheap but needs to be done right either way. I explain problems with insulating a roof using the warm and cold roof construction methods. When you have an un insulated roof you have to live with.

Warm deck flat roof insulation is now the standard way to insulate a flat roof click to enlarge flat roofs for example on extensions bathrooms and dormer windows are not the best of ideas. Unfortunately too many dwellings suffer from this problem.