Consider this scenario: you’re aware of the fact that your existing roof is aging and is in need of work. But the roof still seems to have some value. Therefore, you wonder whether the entire system needs replacement, or if there’s a less drastic option—one that can fix the older roof, without entirely replacing it.
The short answer is yes, this is a possibility. There are circumstances in which a roof can be recovered, if the foundation of it is still in good condition.
One possibility is the addition of an overlay—a full watertight roof system installed on top of a separation board, which separates the old system from the new one, allowing for a new, different type of roofing to be placed on top of it.
A roof recovery of this type typically entails the installation of the separation board, a new membrane, and membrane flashings. Let’s explore this a little deeper:
Separation Board: This is a board made of a traditional cover board material (i.e. gypsum or wood fiber) or added installation (i.e. isocyanurate), which adds greater thermal value. It is installed directly over the old roofing system.
New Membrane: This can be any type of system (e.g. modified bitumen, built up roofing, PVC, TPO, EPDM), but it should match the needs of the existing building.
Flashings: Due to their exposure to the elements—and where they sit, in areas of changes in elevation/direction— the flashings are typically the first area of failure in any roof system. Therefore, they are critical to the successful installation of an overlay. The new membranes should be adhered directly to the substrate, providing weather-tight conditions, which allow the roof to last for another 10-20 years. They are also the most challenging aspect of installation, underscoring the need for an experienced roofer.
Of course there are several factors that determine specifics of the overlay installation, and things that must be kept in mind. Any ballast (e.g. river rock or gravel) must be removed prior to installation of the separation board. Additionally, overlays shouldn’t be installed where existing insulation may be wet. A thermal scan of the roof will identify potential areas of moisture, allowing the roofing professional to identify if any existing roofing and insulation needs to be replaced before installing the overlay. Finally, if an overlay has previously been installed, the existing roofing systems must be removed. Most municipalities limit the number of roofs installed on a structure to two.
Clearly, there are factors that make roof recovery with an overlay challenging, but far from impossible. Experienced roofers can identify and overcome challenges—and in the end, can potentially save you from an entire roof replacement.