If want to add space to your home -- for a home office, for example -- repurposing the garage makes sense. Because your new room makes use of existing space, you don't have to apply for building permits to construct an addition. Most attached garages already have lighting and electrical sockets. When you approach the job of sealing the garage door, decide whether you want to change the facade to make it look like it's a regular part of the house, or whether you just want to leave the garage door in place.
Lock the garage door, and bolt it closed to prevent it from being opened.
Measure the width and length of the garage door's outer perimeter, and carry the width measurement to the walls.
Mark the position of the wall that will be constructed against the garage door on the floor.
Install stud tracking on the floor with concrete screws. Stud tracking is a metal support strip into which 2-by-4-inch wood studs are inserted to support the wall covering the garage door. Drill holes into the concrete floor with a hammer drill. Screw the tracking in place -- this step determines the strength of the wall.
Measure the height of the garage from floor to ceiling, and cut wood studs to this measurement.
Install the wood studs into the tracking, spacing them every 12 inches apart. Reinforce the two ends with two to three more wood studs. Screw the wood studs together to add strength to the corners.
Install the insulation between the studs to keep out drafts from the garage door.
Close in the walls with drywall. Screw the drywall into the studs.
Finish the seams of the wall with joint compound and paper tape. Smooth the joint compound with a feathering knife until it seamlessly blends with the rest of the wall. Paint the wall once it is dry.
Take out the garage door unit to open up the space.
Construct a frame in the garage door opening. Use pressure-treated 2-by-4-inch wood studs to install the base, top plate and wall studs to close in the space. Frame a window or a door opening if you want light to enter the room or have a separate entry.
Apply a bead of waterproof exterior caulk around the framed garage opening.
Affix plywood sheathing to the outside of the garage's new wall. Put in a vapour barrier over the sheathing, and then install an exterior that's complementary or the same as the rest of the house.
Install the window or door.
Insulate the wall on the interior side, and then close it in with drywall. Finish the wall with paper tape and joint compound.
Sand the wall smooth and then paint it to blend with the rest of the wall.