Thursday, August 18, 2011

Roofing: Recover or Replace? (Part 4 - Recovering Roofs)

Recovering Roofs
The installation of a new roofing system over an existing roof (if viable) is an alternative approach to roof replacement. The major advantage to this approach known as recovering is the cost savings associated with not having to remove and dispose of the existing roof membrane. This can be acheived with a variety of materials including cool roof coatings like those from Conklin. Another advantage is the reduction of materials sent to landfills because labor, disposal and trucking costs are high and are climbing faster than material costs.

There is also an opportunity to improve the thermal performance of the roof system because most recovers include the installation of a thin section of insulation or other material to separate the new roof membrane from the existing roof membrane. A final advantage that recover has over replacement is that the existing membrane stays in place, protecting the interior from water damage while the new roof is being installed.

As with repairs, an issue that must be addressed prior to any recover is determining whether moisture is present under the existing system. Trapping water within an existing roof assembly is a problem that often occurs with improperly executed recover projects.

If moisture is present under the existing system, additional investigation is warranted. If the subsurface moisture is extensive — 30 to 35 percent or more of the entire roof area — it may be more practical and cost effective to remove the entire roof system and replace it rather than attempting a recover.

There are many devices and methods used to detect and quantify subsurface moisture. These include nuclear backscatter, infrared imaging and capacitance meters. There are advantages and disadvantages of each system, and these should be explored.

Another factor influencing whether or not a recover project is feasible is establishing how many roof systems or layers are currently in place, which requires making inspection openings. Most modern building codes allow a maximum of two non-ballasted roof systems on a structure, mostly due to the weight associated with the roofing materials. Other code-related issues are wind up-lift and fire resistance, which the building’s insurance carrier may also influence through specific requirements. The length of the warranty required for the new roof also needs to be considered, because many roofing manufacturers will limit the duration for the warranty available on recover projects.

Tomorrow we wrap-up this series with a discussion on replacing roofs. Please check back and feel free to leave us a comment.

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1 comment:

  1. Great post Randy! I think that you covered all of the bases here, the only thing that I would add is the old tried and true core sampling method to detect moisture.