Size Roof Overhangs and Projections to Add Moisture Protection

Roof overhangs and projections such as porch roofs or overhanging floors provide a primary means to deflect rainwater away from building walls. Thus, the potential for water penetration through siding, windows, and doors is minimized. With proper site grading (Chapter 3) and use of gutters (Section 4.2.6), roof overhangs can also help protect foundations from rainwater. The recommendations in this section are generic in nature to provide a simple and practical minimum recommendation. They do not consider all the pros and cons of roof overhangs as related to an integrated design approach (refer to Integrated Design and Construction text box). For example, larger overhangs than those recommended in this section may be important for tall buildings.

Integrate minimum roof overhang widths into a home’s design, as shown in Table 4–1 and Figure 4–1. In addition, porch roofs or floor overhangs should be considered to protect lower story walls, particularly doors and windows. A Decay Hazard Index map is provided in Figure 4–2 to assist in using Table 4–1.