The 2009 International Residential Building Code Section R907 governs the design, materials, construction, and quality of roof assemblies. IRC Chapter 9 Section R907.2 requires structural roof components to adequately support the covering systems and the material and equipment loads encountered during its installation. The strength of a covering assembly can affect its performance, functionality, and relative safety.
Recently, I read an engineering report stating a proposed repair procedure for a hurricane damaged roof system. The subject system consist of two covering layers: an original wood shingle layer and a secondary asphalt roof layer placed on top of the wood shingles. The repair procedure is essentially called for removing individual water and wind damaged shingle and merely replacing them with a corresponding new shingle. And, presumably, each new shingle installed would then connect to, or through, the original wood shingle covering system. As written, this particular re-covering method violated the International Building Code, section R907.2 because it provided no method to secure the structural adequacy of the undering wood shingle roof structure.
Indeed, data and analysis suggest wood shingle systems exposed to prolonged water and wind likely loose some of their structural support adequacy within their damaged areas. As a practical matter, verifying the structural adequacy of the in place wood system is tantamount to its complete removal. This is because the cost of removing, testing, and reinstalling damaged wood shingle systems can easily equal or exceed their full replacement with new covering systems. Knowing this, IRC Section R907.3 "Recovering versus replacement." requires removing all existing layers of covers when installing new coverings when any one of the following conditions exist:
- The existing covering is water soaked or has deteriorated to the point that the existing 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.
4. For asphalt shinglees, when the building is located in an area subject to moderate or severe hail exposure.
2009 International Residential Building Code re-roofing requirements are clear: removing and replacing damaged roof coverings with new roof coverage requires first removing all existing layers of roof coverings if the existing roof covering system is not structurally sound, is composed of wood shakes, or if it has two or more applications of any type of roof covering.
So, if data and analysis shows damaged roof covering assemblies meet one or more of these IRC requirements, all existing covering layers must be removed before installing new coverage.