When finishing your garage, it is important to use a vapour barrier to prevent moisture damage to the insulation. First, install insulation between the garage's wall studs. Then, cover the insulation and studs with a vapour barrier. Always install the vapour barrier on the insulation's warm side, because as warm air exits towards cold air, it starts to condense. The vapour barrier stops the condensation from reaching the insulation.
Place a tube of acoustical sealant in a caulk gun. Cut the sealant's tip off with a utility knife. Squeeze the caulk gun's trigger to expel a bead of sealant. Spread a bead of sealant along the garage wall's top and bottom plates. The top plate is the horizontal board running over the wall studs. The bottom plate is the horizontal board running under the wall studs.
Run a bead of acoustical sealant along the vertical board in the garage's corner. Unroll a strip of vapour barrier. Ask a friend to hold one side of the vapour barrier while you hold the other side. Lift the vapour barrier up to the wall and position the barrier's top edge on the top plate's sealant bead. Place the barrier's bottom edge on the bottom plate's sealant bead and either the left or right side over the corner sealant bead. Use a scissors to cut off any vapour barrier extending past the bottom plate.
Run a thick acoustical sealant bead along the wall stud where the vapour barrier's loose end hits. Position the barrier's loose end over the sealant bead so that sealant holds all four sides of the vapour barrier in place. Cut off the extra vapour barrier with a scissors if it extends past one wall stud but does not quite reach the next wall stud.
Lift a second piece of vapour barrier up to the garage's wall. Place the vapour barrier's right or left edge on the same thick sealant bead as the previously installed vapour barrier piece. Position the barrier's top edge on the top plate's sealant bead and the bottom edge on the bottom plate's sealant bead. Run a thick sealant bead along the wall stud where the end of the barrier hits. Continue until you have covered all the garage's walls with vapour barrier.
Use insulation with an attached vapour barrier.