Originally posted by our friends at modFORM LLC on September 24th, 2020
Have you ever wondered what the purpose of that little two foot section of roof extending beyond the wall of a house or building is really for? And why do some houses have overhangs while others do not?
In this blog, we will give you a brief explanation of the function of a roof overhang or an eave.
FUNCTION
In its simplest form, a roof overhang is meant to protect the siding of the wall below and the building occupants. By extending roughly 12", 18" or 24", this allows any water on the roof from rain or snow melt to be directed out and away from the building.
PROTECT THE OCCUPENT FROM WEATHER
One important function of a roof overhang is to protect the occupant from rain or snow. If an overhang is used in a strategic way, it can be extended over an entry door to give the occupant a moment out of the inclement weather before entering into the building.
These roof overhangs can also be utilized to wrap around a building to give the user a path around the building that will remove them from the weather.
PROTECT SIDING FROM MOISTURE
Similar to above, the roof overhang can protect the building siding from rain and moisture. Think of the roof overhang as an umbrella for the building. By extending the roof a few feet away from the building, this allows for water to be drained and directed away from the walls.
But what about houses or buildings without overhangs? Many houses are constructed without the use of overhangs. In these cases it is very important to choose materials that are water resistant and are not susceptible to moisture. In many cases, masonry, brick or rock may be a good choice.
If a building is constructed from masonry, there is less need to protect these building materials from water as they are not as vulnerable as wood siding.
Climate may also be a factor in the size of the overhang. In dry, cooler climates with very little rain there is less need to protect siding from rain because of the lack of it. In this case, a roof overhang may not be necessary. This one is tricky though. In cool dry climates, no overhang may work but, in dry desert climates, a roof overhang may be important for shading from the sun. Which leads us to the next point.
SHADING
In climates with an abundance of sunshine, it is advantageous to shade the building walls and windows to reduce heat at the interior of the building. Depending on the location on earth, latitude and sun angle, the roof overhang extensions can be situated in such a way to block direct sunlight from entering windows.
In a location such as Seattle, WA, a well designed roof overhang can be designed in such a way to block direct sunlight in hotter summer months when the sun is higher in the sky and it can allow for solar heat gain in the winter when the sun is lower in the sky.
VENTING
Another purpose for a roof overhang is to allow for roof venting. Roofs need to be vented for many reasons such as to avoid moisture build up which leads to mold. Or to reduce the chances or ice dams in cold snowy climates. Perhaps this could be part of another blog. In any case, the roof overhang allows areas to conceal and hide venting for the roof cavity.
STRUCTURE
Something to touch briefly on with overhangs is the support or structure of the overhang. In general for wood construction, a roof overhang can extend from 12"-24" without any special structure. Once the overhang extends above 24", special provisions such as the use of large beams, whether revealed or hidden ( or flush) will be required within the roof framing. Which can increase the cost of framing.
So that's a brief post about roof overhangs. Please let us know if you have any questions or comments below. Thanks for reading!