Insulation For Flat Roof Without Attic

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.

Insulation for flat roof without attic.

You can expect to pay about 55 100 sq ft. We recommend having at least 20 r value worth of material for optimal energy efficiency. Look for water stains on the roof sheathing or damp or moldy spots on attic joists and existing insulation as a clue to where leaks might be. It is important to note when insulation is on the floor of the attic the space between the insulation and the roof deck must be vented to the exterior.

Box out light fixtures. 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. Seal any roof vents into the parts of the attic that are not heated. 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.

New rules and practical interpretation. To insulate a flat roof internally using insulated plasterboard. Try a spray foam insulation kit to fill cavities gaps cracks expansion joints and other sources of air leaks. Water is insulation s enemy.

Rolls are easy to transport and can be cut to the length you need. It is top quality and the most cost effective product for your flat roof. Insulation on the floor of the attic figure 1. It helps resist moisture that can lead to mold or mildew and provides increased sound and thermal insulation.

Leave a clear space between the top of the insulation and the underside of the roof sheathing to allow for roof ventilation. It creates a breeding ground for mold and mildew and ruins the air trapping pockets that block heat flow. For a 1 inch board equivalent of 6 r value. 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.

While expensive the best insulation is polyiso rigid foam. This insulation strategy has not changed in recent code iterations and is not discussed in this article.