The Pitfalls of Installing a New Roof Over an Old One

Roofing replacement comes at a significant cost. Once you calculate the cost of tear down and waste disposal combined with the labour and materials involved in installation, even the cheapest options is likely to cost several thousand dollars. As a cost saving effort, many home owners choose to have their new roof installed over the existing one rather than pay extra for removal. Indeed, this is a common practice among many roofing contractors, but there are several well-documented problems with this type of installation.

Leaks are not Always Corrected

Areas of your roof that have had leaks may not be fixed properly. For most homeowners, roofing replacement is a last resort necessitated by the fact that their current roof does not provide adequate protection. This often means there are leaks, possibly rotting materials, and other problems. When a new roof is installed over a damaged roof, the source of leaks and other damage may not always be corrected and these problems may continue.

Wood Rot will Worsen

Rotten materials will only continue to rot and may even affect the integrity of your new roof. Especially when wood is rotting under asphalt and other materials, these areas are not easily identified unless the existing roof is removed. A lay-over installation further covers rot without adequately correcting the problem. This may lead to more serious structural problems with your roof.

Overlooking Eaves, Rakes and Valleys

During a new installation, the eaves, rakes, and valleys of your home are subject to damage from inclement weather. For example, eaves may be damaged from ice dams, snow build up, and regular freezing and thawing of materials on your roof. These parts should be properly inspected and replaced if they are damaged, and this kind of damage is not always recognized with a lay-over installation.

Moreover, unless your existing roof is removed, there is no way to ensure that the ice and water barrier around the perimeter of your roof and in roof valleys is functioning properly. In fact, this 3 food wide section of your roof is generally replaced during new installation, though this is not the case with a layover roof. Ultimately, certain elements will be outdated and may not function properly with lay-over installation.

Roof Loads become Unbearable

While many building structures can bear the weight of one or even two lay-over roof installations, eventually the weight of the roof may not be supported – especially in older homes. If you eventually decide that a lay-over roof is your best option, you'll have to be sure to discuss the load capacity of roofing structures with your contractor.

Sacrificing Life Expectancy

Perhaps the most compelling reason not to install a new roof over an old one is the life expectancy. Any honest contractor will tell you that lay-over roofs have a reduced life expectancy by as much as 25%. New installations may be more expensive in the outset, but when you consider the life time of your roof, they may actually save you money over time.