Iso Foam In Unvented Attic Ceiling

Spray foam is a very expensive option however.

Iso foam in unvented attic ceiling.

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 allows you to install your bulkheads above the ceiling plane without the need for spray foam insulation. 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. If you don t want to use sips or nailbase there are four basic approaches.

Johns manville aptm foil faced insulation sheathing board is an excellent choice for insulating attics and cathedral vaulted ceilings. When applied to the. Foam board insulation would be a more economical especially if you are supplying the labor see photo. 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.

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. Vented ceiling across rafters.

Two acceptable methods for insulating an unvented attic assembly in all climates are as follows. 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. Im using 2 iso foam board foil faced against my shiplap with one part can foam around the edges to seal it up. In general closed cell foam is the best choice for unvented cathedral ceilings.

However designers of compact roof assemblies must consider vapor permeance and arrangement of the roofing materials to produce acceptable hygrothermal performance and low. 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.

Four options for building an unvented roof assembly. 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.