About the House: Eaves and Deeply Set Windows Discourage House Leaks

By Matt Cantor
Wednesday December 23, 2009 - 09:08:00 AM

Houses leak. Bad news but it’s true. You knew this, so no big news flash, right? What’s not so evident to the uninitiated is why. And that’s such a large set of issues that I won’t attempt to give a quick, glib answer. That said, there are some big chunks of knowledge that experienced builders and a few architects know. So I will try to see if I can lay out some of them, especially since the rains are upon us, and many buildings are leaking now. 

Configuration is key. Water runs according to gravity (when it’s in its liquid form, anyway) and will find its way into anything it can, so the way we design pathways for runoff is absolutely critical. 

On my own house, I’ve had some problems with upstairs doorways that leaked into a lower floor and, while I understand the dynamics of these problems better than most, I’m lazy and I’m cheap, so one of the things I did years ago was to install awnings over some of the most vulnerable areas. It’s simple. Had the original builder had the foresight to install large eaves projections, I wouldn’t have had the problems to begin with. This house, like many in my area is a 1920s Mediterranean-style building with a flat roof (we inspectors would say a low-slope, which is true but less dramatic). Aside from the travesty of the flat roof, the building was designed without eaves. While this may seem a minor issue, it is, in fact, a huge one, because houses with eaves are far less likely to leak.  

Eaves are like umbrellas. They’re like those awnings I had to add. They mean that rain water that would normally get a chance to invade around windows and doors is reduced in volume by a large factor, and this can easily suffice to reduce the invasion to a point where it’s fairly irrelevant. One of the reasons that houses were successfully built and maintained for thousands of years before metal flashings and complex details came along is that roofs were steeply pitched (removing water faster than it can leak) and that these roofs projected well past the wall surfaces on most houses. 

The majority of houses have details around windows and doors that are somewhat vulnerable to leakage. Those houses that have eaves or awnings fare far better and require far less painting and caulking than those that do not. This is true despite the fact that some rain is driven laterally by wind at a speed sufficient to trump even the best eave; it’s a numbers game. 

Water doesn’t do its damage all at once. It’s something that manifests, mostly, over time and with constant abuse. The occasional pelting may allow a bit of leakage, but it is far less likely to leak and will leak far less if the majority of the rain is being cast off by the shape of the house.  

A secret that builders of the past knew well but has been shed with modernity is that windows and doorways that are set deeply into the wall are far less likely to leak. If the sills are steeply pitched, this works better still. 

I have often seen windows sills that were so flat that I could not be sure that they had any pitch at all (without getting a level, anyway) and this is, to me, appalling. How did we forget everything we learned over the course of several thousand years of house building? 

Eaves do other things that are fairly cool—literally. Eaves have thermal conservation properties that can reduce cooling costs (if you’re unlucky enough to live outside of Berkeley where we don’t need much of that). Eaves shade windows and the side of the house when the sun arcs high overhead on hot summer days. They keep the sun out of the interior and keep the exterior walls cool. When winter arrives, the sun arcs low in the south (for those of us living north of the equator) and can enter adding heat and light on a cold, short day. These are concepts that have begun, in the last few decades, to work their way back into our common architectural thinking, but their application still appears rare and unfamiliar. There appears to be far more interest in novelty and style than in those features that can prevent leakage, add longevity, reduce operating costs and save the owner from having to hire contractors.  

For their last act, eaves can do another wonderful trick. They can prevent roof leaks by eliminating porous boundaries from the edge of the building. Flat roofs terminate right above the walls of the building. So when they fail, they are very likely to leak right into those walls. If we’re lucky, they will leak right into the room we’re in. I know this sounds odd but stick with me. Often, because of the configuration of low-slope roofing and the manner of drainage, the leaks into the walls going largely unseen. If you’ve ever seen a stucco house having its skin peeled back to expose a field of rotting wooden substrate, you’ll know what I mean.  

If you’ve owned such a house, you’ll never forget it. When roofs leak along the edge and behind a stucco surface, there isn’t much to see until this surgery is performed, but the damage can cover a hundred square feet and require tens of thousands of dollars in repair costs. A house with eaves, however, is no more likely to leak into the wall than into any other part of the building because there is no boundary where the roof meets the building perimeter. What’s important to understand here is that roofs rarely leak except where there are junctions of some kind.  

I have seen many houses that have had their flattish roofs replaced or overlain with sloped ones endeavoring to escape the woes of their poor upbringings. It’s not something I endorse. My reluctance has been aroused over years of wincing observation of the results: misfit roofs stuck like party hats on sad and unsuspecting homes with their own rich and identifiable breeding.  

Said more simply, sloped roofs added to flat ones usually don’t fit. They look wrong. Occasionally, someone with a sense of scale and good proportion will come along and prove me wrong, and I am thrilled to see it … but it’s rare. Architecture doesn’t work that way.  

And what I evaded in this discussion was that grand eaves and deeply set windows are beautiful. Why are they beautiful? Does beauty stem from utility? Somewhere deep in the cerebellum where accountants won’t peer is there an architectural sub-routing running that expresses itself in terms of beauty and comfort? That’s too cosmic for me, but It’s clear that something true lurks there, and that we know what’s good when we see it, even if the technology manages to escape us.