Recovering versus replacement
New roof coverings shall not be installed without first removing all existing layers of roof coverings where any of the following conditions occur:
1. Where the existing roof or roof covering is water soaked or has deteriorated to the point that the existing roof or roof covering is not adequate as a base for additional roofing.
2. Where the existing roof covering is wood shake, slate, clay, cement or asbestos-cement tile.
3. Where the existing roof has two or more applications of any type of roof covering.
Recovering Versus Replacement
This code implies that recovering of existing roof systems is an acceptable practice — with three key exceptions:
1. If moisture is present in system.
2. If the roof is made up of wood shakes, slate, or tiles.
3. If two roof systems have already been applied.
Some local or state codes have added verbiage to the code indicating that if more than 25 percent of a roof area has moisture present, the entire roof area requires replacement. Moisture analysis can be conducted using infrared (IR) scan, nuclear or capacitance meters.