Insulation For Flat Roof Without Attic

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.

Insulation for flat roof without attic.

While expensive the best insulation is polyiso rigid foam. 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. It is top quality and the most cost effective product for your flat roof. Seal any roof vents into the parts of the attic that are not heated.

Water is insulation s enemy. Box out light fixtures. You can expect to pay about 55 100 sq ft. 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.

It helps resist moisture that can lead to mold or mildew and provides increased sound and thermal insulation. This means lowering the height of the ceiling but may be a better option than insulating externally. For such constructions the principles and benefits of unvented attic construction are similar to that occurring in a single family residence. Leave a clear space between the top of the insulation and the underside of the roof sheathing to allow for roof ventilation.

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. This insulation strategy has not changed in recent code iterations and is not discussed in this article. We recommend having at least 20 r value worth of material for optimal energy efficiency. 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.

New rules and practical interpretation. Insulation on the floor of the attic figure 1. For a 1 inch board equivalent of 6 r value. To insulate a flat roof internally using insulated plasterboard.

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. Try a spray foam insulation kit to fill cavities gaps cracks expansion joints and other sources of air leaks.