All About Eaves

Wood-sided house surrounded by grassy fields and fog
Trent Bell/ Little House on the Ferry

After I posted Buildings can be boxy but beautiful if you have a good eye, Commenter Robert asked "Why have overhangs been eschewed?" I eschewed on this for a while and concluded that the answer is "Because they can." This is in fact a subject that has been discussed on TreeHugger before, but it's time for an update.

Martin House with overhangs
Lloyd Alter / CC BY 2.0

Historic Functions of Overhangs and Eaves

Historically, roof overhangs and deep eaves performed an important function, particularly in wet parts of the country: they keep water off the walls and away from the foundations. Roof overhang is also a function of roof slope; the shallower the roof, the deeper one could build the overhang. Frank Lloyd Wright liked really deep overhangs, so deep that Mrs. Martin hated the Darwin Martin House in Buffalo because the rooms were so dark and depressing. UPDATE: a commenter says this is a myth and provides evidence.

Red angled roof over a house with gray brick facade
Dominic Labbe

In Quebec, where they have lots of snow and want steep roofs, they developed the bell-cast profile where the roof is steep at the top and then bells out at the bottom to get enough overhang. This kept the snow further away from the house.

It was green building dogma in the seventies that roof overhangs should be calculated to let the low winter sun in and block the high summer sun. This only worked on the south facade, however, which limited its application. And, as I noted in an earlier post, it probably didn't work very well at all.

Modern Designs Without Overhangs

I did not insist on roof overhangs on my own house because I wanted a modern look and there were all kinds of technical issues that arose because of the proximity to neighbors. But I miss an overhang when it rains and I want to open a window for some ventilation.

Geoboard siding on a building after rain
Lloyd Alter / CC BY 2.0

It rained last night and one can see on this photo that the siding is clearly wet. But I don't think it will do the Geoboard any harm and it is acting properly as a rainscreen. Behind it, there are high tech membranes like my sticky orange frogs that will help keep moisture out. I don't worry about the solar gain because we can now tune our windows with any solar heat gain coefficient that we desire and facing west, an overhang would have been useless anyway.

On Green Building Advisor, Martin Holladay pretty definitively says that every house needs roof overhangs to "help shade windows in hot weather and reduce the amount of rain that hits your siding, windows, and doors." He shows photos of walls in dire straits and notes:

White worn siding on a house
Olek Lejbzon & Co via Green Building Advisor
A house without roof overhangs leaves siding unprotected and vulnerable, like an orphaned lamb released near a pack of wolves. Unprotected walls suffer high rates of water entry, premature failure of any paint or stain, and premature siding failure.

But much depends on maintenance, and paints, stains, and sealers are dramatically better than they used to be. In my response to Martin's article, Every house should have roof overhangs, except when they shouldn't or can't, I noted that If you do design it carefully, use high quality materials and build it properly, you don't have to be doctrinaire and say "every house should have roof overhangs." But I will have to report back in twenty years.

It's true that roof overhangs really do make sense, protecting and shading the wall, foundations and windows. But how cool is this?