In the past, it was common practice to install a new layer shingles over the first layer of roofing shingles to reduce costs. In some parts of the Chicago area you might even find three or four layers of shingles from the days when building codes were far more lenient. Today such practices are frowned upon. The construction practices today along with the building products such as windows and siding moisture barriers are making the houses more energy efficient and air tight. Often times the only exhaust for a home may be through the attic and the roof. This causes a vapor drive that can weaken a roof deck. Generally, a second layer will only last 7-10 years. Removing all roofing material provide the only opportunity to inspect the condition of the decking to ensure that it will meet the life expectancy of the new roofing materials. Countryside Roofing, Siding and Windows can help you determine how many layers of roofing materials are on your house.