Insulation Directly Against Roof

Foam insulation may be the best idea but this can be costly.

Insulation directly against roof. Updated on august 31 2018 with new information on code changes allowing the use of vapor diffusion ports. Step 2 pull the insulation so that it extends over the top plate of the wall. 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. Position the foam board between the rafters and push it upward until it fits snugly against the underside of the roof deck.

Metal roofs are made from steel copper or aluminum panels. Foam insulation can be used in existing roof structures. The panel attachment in combination with the purlin or truss structure will secure the insulation. Insulation suffocates the roof sheathing thus preventing any convective currents from drying it out.

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. Baffles can be installed and the foam can be sprayed in. However the contractor told us that when cellulose and foam board are installed properly no spacer is needed. The snugness of the foam itself should be sufficient to hold the strips.

Experts usually advise builders that you can t install fiberglass insulation directly against the underside of roof sheathing. I think the best time to have the job done right is when you are putting on a new roof this includes the sheathing. Lay the insulation loosely over the purlin or truss structure the horizontal framework of beams helping to support the roof. Lstiburek takes blame for bad language.

You can install fiberglass insulation against the metal roof and prevent moisture problems if you cover it with a vapor barrier. 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. The old insulation could be removed. Some homeowners choose to use unfaced fiberglass insulation batts.

This can be hard with roofs which are not a straight plane down. 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. If you want to install fiberglass between your rafters you have two basic choices.