Roofing a building requires a substantial amount of labor and expense. Many homeowners consider adding another layer of roofing over the top of the existing roof to save money and time. Consider the advantages and disadvantages before making the final decision on the installation method for a new roof.
Homeowners have two standard options for replacing a shingled roof: tear-off and relay. A tear-off involves removing the entire existing layer, or layers, of roofing materials from the roof. A new layer of roof replaces these layers resulting in just one layer of roofing shingles. A tear-off has a potential life expectancy of 15 to 30 years, according to Christopher’s Roofing, a North Carolina roofing contractor.
Relay roofing, also called a roof-over, involves adding a second or third layer of new roofing on top of the existing layer. A relay has a potential life expectancy of 10 to 20 years.
Condition of the Existing Roof
The condition of the existing roof determines whether you can add another layer of roofing materials. Relaying is not recommended for roofs with existing shingles that are curling, moss covered or splitting. The contractor should inspect the roof for sagging or rotting decking, which indicates problems requiring more than a simple addition of new roofing materials.
The type of shingles for the new roof must be of the same material as the original roof. When placed over heavyweight shingles, lightweight shingles reveal all the ridges and lines from the original roof.
Replacing a roof by simply relaying a new roof on top of the existing roof saves money. The labor costs associated with removing the existing roof are eliminated. In general, the entire re-roofing process takes less time.
Number of Layers
Building codes vary from area to area. Some building codes only allow a maximum of two layers of roofing materials. Homeowners should also check with their insurance company regarding their policy on roofing layers. Standard practice in the construction industry limits the layers of shingles to two due to weight concerns on the roofing structure and the available length of fasteners.
Alternative Roofing Materials
In general, the process of relaying a roof involves shingles over shingles. It may not be possible to relay a roof with other types of roofing materials. For example, Barry Stone, a columnist with the Daily Herald in Chicago, does not recommend relaying a wood shingle roof with asphalt shingles due a compromised nailing surface and weight issues.
Hanson Hiedelberg Cement Group, the manufacturer of Hanson cement roof tiles, cautions that if a roof has been constructed for shingle roofing, the trusses and roof structure may not be strong enough to support a tile roof.
Metal roofing can be installed without removing an existing asphalt shingle roof, according to Tom Black, executive director of the Metal Roofing Alliance, an organization of metal roofing manufacturers, paint companies, material suppliers and industry publications. While it’s recommended as a way to save time and money, the condition of the existing roof must still be assessed before adding a metal roof.