Insulation Directly Against Roof

Position the foam board between the rafters and push it upward until it fits snugly against the underside of the roof deck.

Insulation directly against roof.

Updated on august 31 2018 with new information on code changes allowing the use of vapor diffusion ports. The panel attachment in combination with the purlin or truss structure will secure the insulation. It s not coming from above the roof and it s not some new moisture source resulting from the spray foam. If you want to install fiberglass between your rafters you have two basic choices.

They are used in commercial and residential structures to protect against weather and other exterior elements. But spray foam insulation used at the underside of the roof deck would need to be covered by a thermal barrier and intumescent coatings are commonly used. Experts usually advise builders that you can t install fiberglass insulation directly against the underside of roof sheathing. Baffles can be installed and the foam can be sprayed in.

Some homeowners choose to use unfaced fiberglass insulation batts. Lay the insulation loosely over the purlin or truss structure the horizontal framework of beams helping to support the roof. The snugness of the foam itself should be sufficient to hold the strips. The movement of air into indirect conditioning of an unvented attic is a slow gradual process that will not be noticeable by occupants and typically will not put any strain on the hvac system.

Moisture generated indoors or that infiltrates into the home is responsible for the bulk of the moisture in an attic insulated with spray foam on the underside of the roof sheathing. Insulation suffocates the roof sheathing thus preventing any convective currents from drying it out. However the contractor told us that when cellulose and foam board are installed properly no spacer is needed. Metal roofs are made from steel copper or aluminum panels.

The old insulation could be removed. Lstiburek takes blame for bad language. This can be hard with roofs which are not a straight plane down. Either include a ventilation channel between the top of the fiberglass insulation and the underside of the roof sheathing or install enough rigid foam above the roof sheathing.

Foam insulation may be the best idea but this can be costly. Foam insulation can be used in existing roof structures. Step 2 pull the insulation so that it extends over the top plate of the wall.