Whether you're building your home from cob, cordwood, papercrete or wood it is advisable to give your home a substantial roof overhang to protect the walls from moisture and to keep unwanted mid day sun off the Windows. Yet many homes are built with very short, inadequate overhangs.
Sometimes ignorance or style considerations have been the root cause of this common problem but in many situations the choice is made in order to satisfy economics and government regulation. In any city which counts the overhang in setback requirements you'll find that in order to build to a given distance from property lines builders find it necessary to reduce the overhang. If you must stay back 20 feet and you're on a small lot, chopping back the roof line is usually the only way that the property can be maximized. I've seen this most commonly on small lots in areas where land is very expensive.
Another issue which drives people to create an inadequate roof is taxation. If the roof overhang is considered part of the building footprint and counted in the square footage then these overhangs tend to raise the tax burden for that home.
So in order to prevent homes from being built with inadequate overhangs, the square footage and setback requirements need to be changed so that builders and homeowners are not penalized for good practice. If overhangs were no longer considered in setback requirements and they did not add to the tax burden we would see a general improvement in home durability and energy usage without changing one other thing about the house.
On the West Coast there has been billions of dollars worth of property damage due to the leaky condo issue. Although house wraps, vapor barriers, vinyl stucco, inadequate drip edges and gutters and builder ineptitude were huge contributors to this problem, had these buildings been given substantial overhangs much of the water infiltration problems would have never happened. I'm fond of saying that if you build a large enough overhang you can build your house from talc powder. This may be a slight exaggeration but I preach this to my customers constantly.
I've recycled houses built in the 1880s which contained no rot. They have had adequate roof slope, substantial overhangs and breathable walls with old-fashioned tarpaper under the siding. I've also demolished rotten homes from the 1990s which had short overhangs, not enough roof slope, and vinyl stucco over Tyvek house wrap. Those selling these products preach the value of each one on their own even though it's self-evident that their combined use has led to billions of dollars worth of property damage.
Overhangs are nothing new and no one can patent them. Therefore you won't see any fancy ads promoting them. But they are the most important part of your house envelope since they keep the water off your walls, unwanted sun from the Windows and provide a great spot to pile crap against your house .
With inadequate overhangs any little construction error can lead to water infiltration. Large overhangs cover a multitude of sins and allow for a wide variety of wall materials to be used safely.
Great insight. I totally agree. On the sheds I have built I have run generous overhangs, as much as 3 feet. I find them appealing visually also. I am of the opinion also that is mobile homes could or would follow this practice they would last.
I went to an eco-villiage where about 80% of the cob structures had water problems due to crappy overhangs.
Number 2 on my list of stupid things people do to their houses, is heaping soil against the house to grow plants with no regard to moisture issues. I've seen soil piled a foot above where the concrete ends and wood or stucco begin.
Dale : Can I get a witness ! Dale I have seen Structures with dirt floors and shed roofs tacked onto houses and garages with no foundations, needing the stiffening of adjoining
walls connecting at right angles to keep the whole thing from falling down with dirt up on the side of walls 18'', clad only with Homasote (sp) sheathing ! Big AL !
Success has a Thousand Fathers , Failure is an Orphan
I am a HUGE fan of wrap-around porches, both from a performance point of view and nostalgia.
Lots of Eco homes have ZERO overhang for some insane reason.
"You must be the change you want to see in the world." "First they ignore you, then they laugh at you, then they fight you, then you win." --Mahatma Gandhi
"Preach the Gospel always, and if necessary, use words." --Francis of Assisi.
"Family farms work when the whole family works the farm." -- Adam Klaus
When you look for green building stuff at the book store, there are often pictures of buildings where important features are absent. They call it green since less materials are used. Increased energy costs or lack of durability aren't factored in.
I've seen cold climate cabins on stilts with nothing to block the wind, walls of glass, lack of window flashing ...
Thanks for highlighting this subject Dale. Overhangs are a simple feature that increases the durability of walls from sun and water degradation.
As for politicizing overhangs.. not so sure. In my experience, setback requirements usually dont include overhangs and Ive never heard of taxation based on roof area which must be extremely uncommon. I can think of one very important reason to restrict overhang size which has to do with one of the main disadvantages of big overhangs. As with most things in building, there needs to be balance when it comes to overhangs.
Two major disadvantages of overhangs: roof uplift and reduced natural light.
Coastal areas often have restrictions on overhang depth and those that experience high winds (everywhere?) need to be aware that wider overhangs will increase the risk of roof or truss uplift. The new code required hurricane clips will go a long way to preventing this problem but still, if I had a tornado or 75 mph wind gust headed my direction, I would be wishing for smaller overhangs.
While I agree that porches and wide overhangs can look great from the exterior, nothing kills natural interior light like wrap around porches. In cooling climates, East and especially West porches are advisable to prevent direct angle sunlight into windows and heating up the walls of the house. Porches are easier to account for uplift with the right connections at the support posts.
I think the biggest reason people build inadequate overhangs is that they have higher upfront costs, upfront being the keyword of course. I think rainscreens are a better strategy for protecting walls from weather. Overhangs wont help as much in windy rain events but they can still go a long way to preventing problems especially above windows. People cant flash windows for shit. I still think it would be easy for a house with zero overhangs to outperform the house with big overhangs as long as it had good flashing, rainscreen cladding and perhaps better insulation to account for the increased sun exposure. Just because you see a house with no overhangs doesnt mean its not a high performer although a house with those features AND big overhangs would likely perform better still as long as it doesnt contribute to it getting blown apart.
"If you want to save the environment, build a city worth living in." - Wendell Berry
I've been to houses in the city where the overhang was counted in the setback. This may have been a situation where a variance was given to build closer than normally allowed. I agree with the porch thing. I didn't think of the possibility of blow off. I would think that a single plane roof with the high side pointing out to sea, might be a bad idea. Salt box roofs are designed for high wind conditions. I saw many stately old homes in Savannah Georgia that had big porches. Some buildings had a small glass room poking above the roof that heats up and draws air through the house. Can anyone remember what this is called ?
I've used my new powers to give Brian an apple. He's the high tech energy saving guy around here. Check out his posts. Lots of great info.
That's it. Thanks. Google doesn't work very well when a description is given in the hope of finding a name.
Google Images has many nice photos. I was surprised to find that most were of decorative cupolas that don't ventilate the home. I've seen them on newer houses and made the assumption that they were part of an energy saving plan. Probably not. Hundreds of purely decorative models are marketed to new home builders.
Thanks Dale. I love Savannah. The historic architecture there is unbelievable. I think savannah has never had a direct hit from a hurricane and when it finally does, it will be catastrophic to the old buildings that were not built to current codes.
"If you want to save the environment, build a city worth living in." - Wendell Berry