Iso Foam In Unvented Attic Ceiling

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.

Iso foam in unvented attic ceiling.

Vented ceiling across rafters. Im using 2 iso foam board foil faced against my shiplap with one part can foam around the edges to seal it up. Foil faced iso board can be cost effective insulation for finished attics and cathedral ceilings. In general closed cell foam is the best choice for unvented cathedral ceilings.

Johns manville aptm foil faced insulation sheathing board is an excellent choice for insulating attics and cathedral vaulted ceilings. If you don t want to use sips or nailbase there are four basic approaches. Foam board insulation would be a more economical especially if you are supplying the labor see photo. However designers of compact roof assemblies must consider vapor permeance and arrangement of the roofing materials to produce acceptable hygrothermal performance and low.

Polyiso provides one of the highest r values per inch of any rigid insulation r 6 at 1 inch. 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. Foam filled cathedral ceilings may make sense in some cases. This allows you to install your bulkheads above the ceiling plane without the need for spray foam insulation.

Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls. 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. 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. 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. When applied to the. Attics and cathedral vaulted ceilings. Two acceptable methods for insulating an unvented attic assembly in all climates are as follows.

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. Air impermeable insulation typically spray foam installed to the underside of the roof sheathing. Spray foam is a very expensive option however.