Many homeowners ask whether it is necessary to remove an old roof before installing a new one. They reason that they will save the expense and time involved in removal, and they feel that leaving the old roof gives them an additional layer of protection against leaks. While there is certainly some truth in these statements, leaving an existing roof in place is not always possible, and it may not be the best idea even if removal is not required.
• Many local building codes specify how many layers of shingles are allowed. When a restriction applies, the most common number is two layers. Thus, if you already have two layers of shingles on your roof, you cannot install a third layer without removal.
• Tearing off old shingles provides an opportunity to inspect the deck panels and fix any damages. Cracked or rotted panels may be concealed underneath the shingles, and if they are allowed to deteriorate, your future repair costs could exceed the cost of tear-off.
• Applying new shingles over those that have warped or curled will not yield an attractive roof. The new shingles will not lay flat as they will try to conform to the damaged shingles underneath. This can also prevent the new shingles from sealing as they should, which could result in blow-offs or water penetration.
• Although most manufacturers’ warranties are valid when shingles or metal roofing systems are installed over an existing layer, all warranties contain conditions under which they may be declared invalid. One crucial requirement is that installation must meet the manufacturer’s specifications. If a certain type of shingle (or metal roof) is not approved for installation over an existing roof, the manufacturer could void the warranty.
• Depending on type, asphalt shingles typically weigh between 180 and 360 pounds per square, which is a measurement that is equivalent to the shingles needed to cover 100 square feet of roof. (The square footage of a roof will be more than the square footage of the home as the slope of the roof increases the surface area of the roof.) If your roof requires 20 squares of shingles, the total weight of the shingles alone will be between 3,600 and 7,200 pounds. At the higher end, you will be adding more than the weight of a Hummer to your roof. If you already have a layer of heavyweight shingles, your roof trusses might not be able to support the demands placed on them.
If you are not certain whether you can (or should) apply a new roof over an existing one, seek the help of a reputable roofing contractor. Alpha Roofing has more than 30 years of industry experience and an outstanding reputation for integrity, quality and customer service. We install asphalt shingles as well as metal roof systems, offer roof repairs, install guttering and skylights, repair chimneys and provide many more roof-related services. You can use the form on our website to request a free quote, or you can reach us at (512) 777-1086.