Insulating A Vented Roof

For the same reason insulation shouldn t touch the roof s underside.

Insulating a vented roof.

Foam insulation can play an important role in both vented and un vented roof assemblies. You could insulate the roof the traditional way. Because of limited space between the roof sheathing and ceiling joists a low slope shed roof can be difficult to insulate properly. You must meet the same minimum code requirements for the spray foam layer and the total assembly as for the rigid foam plus air permeable insulation approach.

Then insulate below with fiberglass or cellulose add a vapor retarder and your finish ceiling. Covering up the soffit vents with loose fill or batts which can happen if you stuff insulation along the eaves is a huge no no. In an un vented roof foam can serve as the air barrier and vapor retarder and prevent moisture from getting in to the roof cavities. In this energy smart homes article senior editor martin holladay explains how to insulate a vented low slope shed roof using a combination of intake vents and cupolas.

When hvac equipment is in the attic insulation and an air barrier at the roof line brings that equipment within the conditioned enclosure envelope thereby allowing it to operate in more favorable temperature and humidity conditions without air leakage and heat loss gain directly to the exterior. Air can move through the attic space freely and the floor of the attic is insulated to thermally separate the unconditioned attic from the living spaces below. Cathedral roofs especially need a lot more insulation between the ceiling and the rafters because there usually isn t any attic space. All insulation materials require proper venting.

In a vented roof foam can seal the openings and serve as an air barrier and a vapor retarder in addition to its insulating function. That is create a vent channel above the insulation with low and high vents. A layer of spray polyurethane foam can be installed against the underside of the roof sheathing with the rest of the rafter cavity filled with air permeable insulation. While fiberglass insulation is an excellent and effective product for insulating most building cavities in areas where there is extra risk of trapping moisture and thus rot or mold infections such as crawl spaces and cathedral ceilings where roof venting may be absent or minimal we prefer to use closed cell foam insulation products or spray in icynene foam insulation.

Spray foam with air permeable insulation. The airflow from the soffits to the ridge vent keeps the roof cool and prevents ice dams and the material will block that flow.