In either case you will need to follow the general steps below to insulate your garage roof.
Insulating garage roof trusses.
Water is insulation s enemy.
Some do it yourselfers commonly forget to leave air space between the fiberglass and the underside of the wood roof sheathing.
However if you have a cathedral style garage roof you will need a scaffolding to get into the upper areas of the roof.
It s about time i had a better work environment.
I am planning on insulating and finishing the outside walls.
This is part 1.
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To answer some of your questions.
There are many methods that you can use for insulating garage roof trusses but the most popular one is definitely the foam board.
Look for water stains on the roof sheathing or damp or moldy spots on attic joists and existing insulation as a clue to where leaks might be.
If you are insulating the garage ceiling not only by the truss level but also up by the roofline then you must leave at least 1 1 2 to two inches of air between the fiberglass and the underside.
Insulating garage roof trusses.
It creates a breeding ground for mold and mildew and ruins the air trapping pockets that block heat flow.
You should use some foil tape to make sure that the insulation is stable on the roof edges.
That s the wall you see in one of the pics.
Box out light fixtures.
Make sure that all of the pieces are the same size so that they fit into the trusses.
The tape will also make sure that there is an air pocket available in the insulation.
To install the insulation overhead you need to staple the pieces to the roof trusses.