Iso Foam In Unvented Attic Ceiling

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.

Iso foam in unvented attic ceiling. It is also one of the most expensive and most building inspectors will not allow it to be left uncovered for fire code reasons. However designers of compact roof assemblies must consider vapor permeance and arrangement of the roofing materials to produce acceptable hygrothermal performance and low. Foam board insulation would be a more economical especially if you are supplying the labor see photo. This is done by using what is referred to as air impermeable insulation such as rigid foam board or spray foam.

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. Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls. 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. Vented ceiling across rafters.

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. Spray foam is a very expensive option however. When applied to the. Four options for building an unvented roof assembly.

In general closed cell foam is the best choice for unvented cathedral ceilings. If you don t want to use sips or nailbase there are four basic approaches. Foam filled cathedral ceilings may make sense in some cases. Foil faced iso board can be cost effective insulation for finished attics and cathedral ceilings.

Attics and cathedral vaulted ceilings. Im using 2 iso foam board foil faced against my shiplap with one part can foam around the edges to seal it up. Air impermeable insulation typically spray foam installed to the underside of the roof sheathing. This allows you to install your bulkheads above the ceiling plane without the need for spray foam insulation.

Johns manville aptm foil faced insulation sheathing board is an excellent choice for insulating attics and cathedral vaulted ceilings. Two acceptable methods for insulating an unvented attic assembly in all climates are as follows. 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.