Filed Under:Claims, Catastrophe & Restoration

Raising the Roof on Wind-Resistant Technology

Understanding Building Codes and Design

According to the Institute for Business and Home Safety (IBHS), roof cover damage continues to be the largest, most frequent source of non-surge related failures related to hurricanes1. In response, roof covering manufacturers have provided a multitude of products that have demonstrated through independent testing to be able to withstand design event forces. However, it is apparent in the wake of recent windstorm events that much is lost in translation between the idealized laboratory setting and an actual constructed roof. This article will provide a brief review of the current codes, design, and selection process. It will also present a number of common construction-related defects that result in the loss of millions of dollars annually.

The selection of the roof covering in a hurricane-prone region would likely start with the locally adopted building code. For most of the U.S., the building code is likely a recent version of the International Building Code2  with local- and regionally specific, amendments. Some jurisdictions—Florida, for example—have specific codes that apply. The purpose of the code is to set a minimum standard of construction and design for the purpose of life safety. It typically does not purport to address other aspects of the functionality of the roof that might include resistance to water infiltration, service life expectations, hail resistance, and other functions that the facility owner may also require. Another distinction to make is that codes, especially those related to commercial buildings, have become less prescriptive and more performance-based in the last few decades. The code dictates the design criteria but not the number of fasteners per square foot.

Adhesion Resistance Standards
Fully adhered systems are required to meet the same resistance standards as the mechanically fastened systems, given that the location and application are the same. Also, like the mechanically attached systems, the adhered applications are only as strong as their weakest component.

With a ‘hot-moped’ application the temperature of the asphalt when applying the insulation or overlying plys of felt becomes critical to its adhesion. Asphalt has an Equiviscous Temperature (EVT) range that is type specific and represents the point at which the asphalt has the ideal viscosity of workability and adhesion between the layers4. Application of the asphalt below the EVT can prevent the asphalt from penetrating the felt and creating the appropriate bond. Working with asphalt above its EVT can breakdown and cause degradation of the asphalt. Figure 4 depicts an example of the blow-off of a membrane where asphalt was applied below its EVP. This is evident by the smooth surface of the asphalt which is indicative of lack of transfer between the asphalt and the adjoining layer. Also noted in Figure 4, proper inter-ply adhesion would be expected to cause some delamination of the insulation.

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