If there is a floor you will need to remove it to properly insulate the roof rafters.
Insulate roof rafters properly.
Airspace from the soffit to the ridge by installing a continuous air chute in each rafter bay.
Additionally insulation serves as a way to enhance sound proofing on the uppermost envelop of your house.
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.
In finished attic rooms with or without dormer insulate 2a between the studs of knee walls 2b between the studs and rafters of exterior walls and roof 2c and ceilings with cold spaces above.
Place the plastic sheeting on top of the rolled insulation.
To install the air chutes staple them directly to the roof decking.
Attach this roof and attic insulation treatment using foam baffles to ventilate insulate and channel cold and hot air to roof vents before insulation is add.
Staple plastic or foam baffles to the roof sheathing near the eaves to keep the material away.
For the same reason insulation shouldn t touch the roof s underside.
The current trend is for a warm roof where insulation is installed between the rafters thereby keeping the roof timbers warm.
Do not use plastic sheeting in this case.
So before insulating go around the garage with a can of low expanding spray foam and seal all gaps and cracks that let in the daylight.
You can insulate the walls ceiling and door of the garage to the highest r value possible but if you fail to fill those air gaps you ll still be wasting a lot of heat.
To effectively ventilate your roof create a 1 in.
The first decision is whether to insulate a pitched roof at ceiling or rafter level.
Unlike solid insulation products that require careful measurement cutting and fitting spray foam can cover even the most uneven surface instantly.
How to insulate a roof.
If your attic is going to be converted into livable space then you will need to insulate the roof rafters.
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.
2d extend insulation into joist space to reduce air flows.
Insulating in and around your roof attic space also prevents long term damage from moisture build up or ice damming which results from the warm air trying to escape through the apex of the roof but instead heating up the snow.