Walls are best spray foamed when there is full access to the area. Most of the time this is during the renovation phase of a home or in new homes. The walls are important to insulate because this is where all the electrical outlets and plumbing pipes are located. Cold air tends to make it’s way through electrical outlets because traditional insulation does not seal around them like spray foam does. Another issue common in walls are frozen pipes. Spray foam encapsulates pipes to ensure they never freeze.