Insulation Directly Against Roof

Experts usually advise builders that you can t install fiberglass insulation directly against the underside of roof sheathing.

Insulation directly against roof.

Insulation suffocates the roof sheathing thus preventing any convective currents from drying it out. 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. 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. You can install fiberglass insulation against the metal roof and prevent moisture problems if you cover it with a vapor barrier.

Metal roofs are made from steel copper or aluminum panels. Foam insulation may be the best idea but this can be costly. They are used in commercial and residential structures to protect against weather and other exterior elements. 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.

Foam insulation can be used in existing roof structures. The snugness of the foam itself should be sufficient to hold the strips. However the contractor told us that when cellulose and foam board are installed properly no spacer is needed. Lay the insulation loosely over the purlin or truss structure the horizontal framework of beams helping to support the roof.

Step 2 pull the insulation so that it extends over the top plate of the wall. Updated on august 31 2018 with new information on code changes allowing the use of vapor diffusion ports. I think the best time to have the job done right is when you are putting on a new roof this includes the sheathing. Position the foam board between the rafters and push it upward until it fits snugly against the underside of the roof deck.

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. Lstiburek takes blame for bad language. Baffles can be installed and the foam can be sprayed in. The old insulation could be removed.

The panel attachment in combination with the purlin or truss structure will secure the insulation. This can be hard with roofs which are not a straight plane down. I know that placing fiberglass insulation directly against the roof decking is a no no as fiberglass insulation requires separation with a spacer to allow for proper ventilation to prevent mold growth ice damming etc.