Insulation For Flat Roof Without Attic

For a 1 inch board equivalent of 6 r value.

Insulation for flat roof without attic.

Leave a clear space between the top of the insulation and the underside of the roof sheathing to allow for roof ventilation. In most cases it should be possible to insulate each rafter space all the way down to the eaves and over the top of the exterior wall. Because most flat roofs don t have an attic crawl space or venting the insulation must go underneath the roof s covering on the exterior of the home or be placed on the inside of the home. While expensive the best insulation is polyiso rigid foam.

Box out light fixtures. It is top quality and the most cost effective product for your flat roof. Insulation on the floor of the attic figure 1. You can expect to pay about 55 100 sq ft.

This insulation strategy has not changed in recent code iterations and is not discussed in this article. It creates a breeding ground for mold and mildew and ruins the air trapping pockets that block heat flow. Water is insulation s enemy. To insulate a flat roof internally using insulated plasterboard.

New rules and practical interpretation. We recommend having at least 20 r value worth of material for optimal energy efficiency. This means lowering the height of the ceiling but may be a better option than insulating externally. Depending on your climate you ll need r 30 to r 49 to meet code which is 5 to 8 1 2 inches of polyiso rigid foam which is r 6 per inch.

Rolls are easy to transport and can be cut to the length you need. But spray foam insulation used at the underside of the roof deck would need to be covered by a thermal barrier and intumescent coatings are commonly used. You probably don t have to meet code of course retrofitting insulation on a funky old house but it s not a bad thing to strive for. Seal any roof vents into the parts of the attic that are not heated.

It helps resist moisture that can lead to mold or mildew and provides increased sound and thermal insulation. For such constructions the principles and benefits of unvented attic construction are similar to that occurring in a single family residence.