Optimum Roof Overhang

How roof overhangs work.

Optimum roof overhang.

Overhangs are most effective for south facing elements in the northern hemisphere and at midday. Roof overhangs should be no more than 2 feet wide. Oversized overhangs can increase the risk of roof or truss uplift. For instance several features of a window will influence gain of solar heat and shade.

Optimum overhang dimensions for energy saving 295 sun fig. Roof construction and materials considerations roof decking. Roof overhangs might look relatively routine but there is a lot of design thinking that goes into creating the optimal dimensions for each one. You can use the free software sketchup to draw the house and it will draw sun shadows for any date time at your location.

They are essential for framing and shading windows reducing splashback and getting rain to fall far enough away from the foundation. The optimum depth varies with the latitude and the type of climate. Doing so keeps basements and crawlspaces dry and it also helps to. Roof and overhang systems should be designed to resist wind uplift especially in hurricane prone regions.

For high wind resistance use 7 16 inch or 19 32 inch plywood or osb roof decking attached with nails not staples. Figure 2 illustrates how this is possible. Geometry of overhang separated from top of window. There isn t general rules to size an overhang.

180tan 10 in order to estimate the radiation received by windows with overhangs the beam diffuse and reflected com ponents of irradiance must be estimated as functions of time and day of the year. 24 dec 2012 02 45 pm. Because the sun travels a higher path in the sky in the summer than in winter the overhang blocks. Borst passive solar roof overhang design calculator.

Roof overhangs at the eaves and rakes protect the walls below from rain and sun. Borst engineering construction llc competence integrity and professionalism are integral to all that we do. An important component of passive solar design is calculating building openings doors and windows and roof overhangs. Those larger than 2 feet wide have to withstand very high uplift so they should be engineered.

If the building element bears more than about 30 off true south the effectiveness of an overhang as with any solar feature begins to decrease significantly. Jonr senior member posts 5341. But are they really necessary.