Overhangs Are Underrated

Many modern architects avoid overhangs like the plague. Overhangs are “uncool,” they say, preferring clean, minimal geometry without protrusions or ornament. To be frank, I’m conflicted. On the one hand, I agree that there is something seductive about seeing that diagonal roofline seamlessly transition into the wall. If the roof and wall are made of the same continuous material, even better. On the other hand, a lack of overhang can leave walls susceptible to wind-driven rain which can lead to premature weathering, mold, and freeze-thaw damage.

Overhangs are especially important in rainy Vancouver, where we get around 50 inches of rain annually. BC Housing conducted a study to examine how overhangs of different lengths affect wind-driven rain on a facade. Researchers attached a retractable awning to the roof of a six-story building with no overhang. They measured wall wetting at different awning lengths, with 1.2 meters being the longest.

They found that the 1.2-meter awning prevented 90–99% of wind-driven rain from hitting the facade 0.6 meters below the roofline. It also reduced exposure by 90% across the upper 15% of the facade and by 60% across the entire facade. This is a significant reduction in rain exposure. In shorter buildings, the effect would likely be even more pronounced because the overhang could protect a larger percentage of the facade. That means less water reaching windows, which are a vulnerable point.

As discussed in another blog post, overhangs are also useful for blocking the sun and avoiding overheating in summer. They’re a simple, fundamental element of architecture, but they’re multifunctional, and best of all, they’re not expensive. Overhangs are standard and simple to build.

The thing is, it’s completely possible to design modern-looking buildings with overhangs. There are many beautiful examples around the city. So if you’re building a house, keep that in mind.

Source: BC Housing, Using Overhangs to Reduce Building Facade Exposure to Rain (2018)