Should You Insulate Your Roof Rafters

Attic moisture problems are often the result of heated air from the living space rising up into the attic which is not heated.

Should you insulate your roof rafters.

In order to avoid damage to the roof deck you should insulate ceilings to create an air barrier between the living space and an unfinished attic or airspace underneath the roof deck. If your attic is often used or perhaps you plan to convert it in the future you will need to insulate the inner surfaces of the roof. For the same reason insulation shouldn t touch the roof s underside. Insulating between rafters will do no good because the attic should be ventilated and the rafter insulation would be between two unheated spaces.

You can also add rigid foam insulation under the rafters which adds r value and eliminates thermal bridging through wood rafters. The first decision is whether to insulate a pitched roof at ceiling or rafter level. If there is a floor you will need to remove it to properly insulate the roof rafters. Do not use plastic sheeting in this case.

If you have vents in the walls of the attic or in the roof ridge then the insulation can go all the way to the roof. If your attic is going to be converted into livable space then you will need to insulate the roof rafters. If the plastic sheeting is in pieces overlap the pieces by 8 inches and staple it in place directly to the roof rafters and the wall. Polyurethane or polystyrene spray foams can provide thorough coverage to roof rafters and attic walls in much less time than is needed for other materials.

Place the plastic sheeting on top of the rolled insulation. 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. Whether or not there is an inner roof lining and the total thickness of the roof structure. You can add insulation to the floor.

The idea is to allow some air to circulate through some part of the attic under the roof but outside the insulation to prevent moisture build up. The airflow from the soffits to the ridge vent keeps the roof cool and prevents ice dams and the material will block that flow. Consider using high density r 30 batts which are as thick as r 25 batts but fit into 2x10 framing. A vent baffle should be installed between the insulation and the roof decking to maintain the ventilation channel.

Install ventilation baffles into the space between the rafters before you install the insulation usually by stapling into place. Unlike solid insulation products that require careful measurement cutting and fitting spray foam can cover even the most uneven surface instantly.