Iso Foam In Unvented Attic Ceiling

Polyiso provides one of the highest r values per inch of any rigid insulation r 6 at 1 inch.

Iso foam in unvented attic ceiling.

Two acceptable methods for insulating an unvented attic assembly in all climates are as follows. Johns manville aptm foil faced insulation sheathing board is an excellent choice for insulating attics and cathedral vaulted ceilings. 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. Most unvented attics incorporate spray polyurethane foam spf on the underside of the roof deck and attic walls.

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. However designers of compact roof assemblies must consider vapor permeance and arrangement of the roofing materials to produce acceptable hygrothermal performance and low. Foam filled cathedral ceilings may make sense in some cases.

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. If you don t want to use sips or nailbase there are four basic approaches. 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. Vented ceiling across rafters.

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. Attics and cathedral vaulted ceilings. 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. Im using 2 iso foam board foil faced against my shiplap with one part can foam around the edges to seal it up.

When applied to the. In general closed cell foam is the best choice for unvented cathedral ceilings. Air impermeable insulation typically spray foam installed to the underside of the roof sheathing. This is done by using what is referred to as air impermeable insulation such as rigid foam board or spray foam.

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