Install the furring strips vertically or horizontally on top of the wall studs, screwing them in with a hand-held drill. Check their straightness with a level and adjust if necessary.
Spray the furring strips with an industrial-strength adhesive. Hold the spray 8 inches away and make even back and forth movements, making sure you cover all of the strips uniformly.
Press a sheet of foam insulation immediately onto the furring strips, starting at the far left side of the wall. Check to make sure the insulation is level; adjust it if necessary. Press it firmly against the wall for five to 10 minutes before moving on and repeating with the next sheet of foam. If necessary, use a clamp to help secure the insulation while the adhesive dries.