Typical roof overhang size

The construction of a roof overhang is one important way that homeowners can protect the exterior of their home and preserve its value. They can also include certain architectural features that make overhangs more than just functional parts of the home.

In designing the overhanging part of a roof, you will need to keep in mind certain key features: the amount of shading that you would like for your windows and doors; the amount of rainfall in the area around your home; and the balance between solar heat gain and shading you desire.

In general, roof overhangs offer an effective solution for how to protect windows, doors and entryways. If the roof overhang is not big enough, then the only way to protect these windows, doors and entryways is by recessing them into the thick exterior wall, or by installing special casing and flashing for each door or entryway. Obviously, the easiest and most effective roof strategy is simply to build a roof that is wide enough to provide protection.

Purpose

The typical roof overhang serves six basic purposes:

  • Help to shade windows in hot weather
  • Reduce the amount of rain that hits the exterior of the home
  • Provide protection for doors and entryway
  • Keep basements dry
  • Protect the foundation from excess water runoff
  • Help to regulate the temperature of the home

If there are improperly sized overhangs, then a home will tend to overheat in the summer and it will be at particular risk of water entry to doors and windows. In a worst case scenario, all of the exterior damage from the rain and splashback will lead to premature siding rot. If you tour suburban neighborhoods with older homes, you can often see examples of housing exteriors where panels appear to be coming off the house. This is an obvious sign that there is something wrong with the dimensions of the roof overhang framing. Homes with sheds can have these problems, too.

Problems

There are two common problems encountered with roof overhangs:

  • The roof overhang is too wide
  • The roof overhang does not extend far enough

In the first case, the overhang is simply too big for the home. This leads to a situation where there is an excess amount of shade and the exterior of the home appears dark and gloomy. A related problem is that the roof is actually at greater risk of wind damage. Moreover, in winter months when the supply of sunlight is limited, the “gloominess” factor is only magnified.

In the second case, the overhang does not provide enough protection. This means that rain will tend to drip next to the foundation and perhaps enter the basement area. It also means that it will be more difficult to reduce splashback. And the more splashback there is, the greater the potential is for siding rot. It also means that there is not enough shading for the windows. This leads to the situation where windows receive too much sunlight during peak hours of the day, especially during the summer.

This situation where the overhang does not provide enough protection is especially common with more modernist architectural styles, where the emphasis is on producing either sleek, curved buildings or boxy, highly angular buildings. It is also an issue with metal roof overhang.

There is also one more problem to take into consideration: wind. The roof overhang length must be properly engineered to resist wind uplift. This is particularly true in geographical regions where high winds are a common issue.

Roof strategies

Home architects have a number of different options when they are looking to protect doors, entryways and windows:

  • They can make the overhang of the main roof wide enough to protect them
  • They can integrate a gable roof overhang or roof crickets with the main roof to protect them
  • They can attach a smaller roof to the wall above every door or window
  • They can create a recessed entry, in which doors are set back from the exterior plane of the wall

If the home only has one level, the standard roof design strategy is clear: make the main roof wide enough to protect all windows and doors. However, there are more options if the home has multiple stories, or if the roof has different slopes and angles. Here, you will need to pay more attention to how any rain runs off the roof. You want to make sure that any water is landing far enough way from the foundation, as well as from the doors of the home. Metal roofs also require particular attention, especially the length of flat metal roofs.

The tradeoff between solar heat gain and shading

For homes built in the Northern Hemisphere (i.e. America and Canada), the most important windows and doors to keep in mind for any roof strategy are the south windows. In the Northern Hemisphere, north windows do not receive much sun, and are not a typical issue.

For the south side of the home, you should follow basic solar design principles. In short, that means that the roof overhang should be of sufficient dimensions to optimize the amount of shade during the warm summer months, but not be so large that they do not allow full sun exposure during the cold winter months.

There are actually mathematical rules and architectural guidelines that can help you determine the optimal roof dimensions. These guidelines are useful in the construction of any gable, or any cantilevered or flat roof.

The goal is to balance the amount of solar heat gain and amount of shading. In hot climates, the general rule of thumb is to lengthen and extend the overhang. In cold climates, the general rule of thumb is to shorten the overhang so that it does not extend as far.

You can immediately see why this makes sense. In a hot, sunny climate, you want to maximize the amount of shading; in a cold climate, you want to minimize the amount of shading. That’s why there can be widely differing architectural styles for homes, depending on where you are in the country. In America, for example, low-slung homes in the hot Western desert areas will have very different appearances than the stately mansions and homes in the colder New England area.

Eaves

An eave is the edge of the roof that overhangs the face of a wall and normally projects beyond the side of a building. Eaves form the overhang to distribute water clear of the walls. They also help to frame windows on upper stories. That is their functional purpose.

However, there is also an architectural purpose to them. In the Italianate style of architecture, for example, eaves are decorated with decorative support brackets that appear to be holding up the roof. In other cases, there are other architectural flourishes directly under the length of the eaves.

Options for homes

Thus far, we’ve primarily considered roof overhangs from the perspective of single-storey homes. But what about multi-storey homes? Or what about homes with flat or metal roofs? Or what if your property has a shed? Here are several different options to consider:

  • Brow roofs
  • Gable-end overhangs
  • Crickets
  • Cantilever roof overhangs
  • Shed covers

Brow roofs are found on multi-storey homes. They are essentially mini-roofs designed to protect each storey of the home individually. A brow roof is a narrow roof attached to the wall at the level of the first-floor ceiling. It can be made of metal.

Gable-end overhangs (also known as “rake overhangs”) extend all the way to the peak of the roof. In extreme versions, they appear to create the prow of a ship, and are thus known also as “prow overhangs.” The peak of the roof is a long way from the base of the wall, so these overhangs are less effective, in general, than traditional eave overhangs in protecting the home. They extend too far. You can think of this logically – there is simply much more potential for rain splashback, especially in very windy conditions.

A cricket is a ridged structure that is shaped to divert water on a roof around the high side of a chimney, or any part of the roof where there are multiple levels. It can be made of metal. The cricket is usually the same pitch as the rest of the roof. If you look at many buildings, you’ll immediately see them – they appear to be gently sloping “bulges” that surrounding protruding parts of the roof such as the chimney. The cricket helps the rain flow more easily off the roof and away from the nearest wall. This is done to protect the foundation and parts of the basement.

A cantilever roof overhang is one way to really give a really distinctive look to your home. A cantilever is a rigid structural element anchored only at one end to a vertical support from which it is protruding. Using a cantilever means you don’t need external bracing. Cantilevered structures are popular for homes with balconies. To create a cantilever properly, you will need to know plenty about physics – like torque and rotational equilibrium.

A shed overhang is an easy and effective way to protect your shed. You can add 3 ½ to 5 ½ inches to the top. This will keep rain away from your shed.

Conclusions

Roof overhangs might look relatively routine, but there is a lot of design thinking that goes into creating the optimal dimensions for each one. They are essential for framing and shading windows, reducing splashback, and getting rain to fall far enough away from the foundation. Doing so keeps basements and crawlspaces dry, and it also helps to preserve every part of the exterior of the home. If rainfall is constantly allowed to splash up against the siding of the home, this could lead to premature siding rot. That’s not just an architectural eyesore – it could also require very expensive repairs.

Having the right overhang is also essential in regulating the heat and temperature of a home, especially in very hot or summer climates. Finally, a large enough roof overhang is a great way to stay dry and provide enough room for opening up an umbrella when entering and exiting a home during inclement weather!