Iso Foam In Unvented Attic Ceiling

Johns manville aptm foil faced insulation sheathing board is an excellent choice for insulating attics and cathedral vaulted ceilings.

Iso foam in unvented attic ceiling.

An alternate to spray foam insulation in an unvented attic is plenum trusses which allow you create a reverse bulkhead above the ceiling plane that is insulated. In the normal vented attic areas flat ceiling but very limited head room accessibility in attic is there any advantage to sheathing the ceiling with rigid foam board below the ceiling joists infilled with batt insulation and overlaying with drywall as opposed a thicker layer of more inexpensive attic batt insulation no rigid foam overlay. Air impermeable insulation typically spray foam installed to the underside of the roof sheathing. Foam filled cathedral ceilings may make sense in some cases.

Polyiso provides one of the highest r values per inch of any rigid insulation r 6 at 1 inch. Foam board insulation would be a more economical especially if you are supplying the labor see photo. This allows you to install your bulkheads above the ceiling plane without the need for spray foam insulation. Attics and cathedral vaulted ceilings.

Spray foam is a very expensive option however. Vented ceiling across rafters. In general closed cell foam is the best choice for unvented cathedral ceilings. Four options for building an unvented roof assembly.

Ill use rockwool batts to fill the rest of the cavity 3 5 and do a 1 foam board unfaced along the underside of the rafters for thermal bridging. Foil faced iso board can be cost effective insulation for finished attics and cathedral ceilings. If you don t want to use sips or nailbase there are four basic approaches. When applied to the.

In buildings where there is no roof venting anyway and where ventilation is difficult or impossible to achieve an un vented well insulated hot roof can provide a high r value ceiling and may be the second best alternative to preventing ice dam related leaks in cold climates. This construction approach was first used in the 1970s and it has been implemented much more widely since it was first included in the international code council s icc model building code in 2007 irc section 806 4. Unvented roof systems where the insulation and air barrier are applied directly to the underside of the roof deck are common in applications where designers are seeking cost effective and energy efficient roof assemblies. This is done by using what is referred to as air impermeable insulation such as rigid foam board or spray foam.

It is also one of the most expensive and most building inspectors will not allow it to be left uncovered for fire code reasons. Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls. Unvented roof assemblies should be insulated either with air impermeable insulation rigid foam or spray polyurethane foam or with a combination of foam and air permeable insulation.