How durable is practical for a conventional light-framed house?
This question comes from Calgary, Alberta, which is (barely) in climate zone 7B. For those who are unfamiliar, Calgary would have a fairly extreme continental climate but for the periodic Chinook (foehn) winds that frequently raise wintertime temperatures by 30 or 40 degrees Fahrenheit. (This both to pretty extreme freezing and thawing cycles and to a climate that is, at times, somewhat more extreme than its number of HDDs would suggest.)
I am of the view that, if a house is to be considered green, it should be durable so that the ecological consequences of its construction are spread out over a reasonable period of time. The more resource-intensive the structure, the longer it is obligated to last. As a modern, resilient home is very resource-intensive, I think it should therefore last a long time.
While some of the concerns about building longevity are independent of building technique, e.g. good siting and the ability of a structure to “learn” through re-configurability and disentangled assemblies, my question relates to physical capabilities.
I have been researching various construction techniques and methods. While it is unquestionable that certain building methods have resulted in very long-lasting structures (e.g. heavy timber, stone and masonry mass walls), I am a bit less certain about the expected lifespan of a conventional light-framed house.
How long could a modern light-frame house be built to last if done intelligently, with proper attention to management of air/vapour and water leaks? Is plywood sheathing likely to last more than a century or would the durability-inclined builder be obliged to use board sheathing for diaphragms and shear walls? Have our increased knowledge and technical abilities counteracted the longevity pressures that come from cheaper materials and stricter energy-efficiency standards? Is it at all practical to build a conventional light-framed house today to last 150 years or more, or would heavy timber be better for this use?
Sorry for the huge question here – I’m hoping to get some information on this.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
If a house is maintained, its basic structure (standard framing or advanced framing) should last for a very long time. But most houses will not remain livable -- at least by modern standards -- if they are left to the weather.
Water and insects are what ruin houses. If you preven these things from entering the house a house will last forever. The disposable wear items will eventually wear out and need to be replaced ( paint, caulking, carpet, protective finishes, roofing) but if you keep up with theses things the structure will be protected.
Every house needs maintenance. As Steve pointed out, the key is keeping water out. And, as Kurtis noted, insects can cause problems in some climates (although insects usually prefer damp houses, so moisture is always a factor).
I used to be a roofer. If you want your house to last a long time, find a good roofer.
I suppose if you are a millionaire who is obsessed with building longevity, you might want to build a poured concrete house with a stainless-steel roof. You can do it if you want to. But such a house will still need windows that can break, and will require insulation that may deteriorate, and will need interior finishes that are more comfortable than concrete. All of these components need maintenance.
Finally, as architects always remind us, no one is going to maintain an ugly house. If you want a house to be well maintained, you have to design a house that people fall in love with.
For more ruminations on these topics, see these articles:
Green Homes Don’t Have To Be Durable
Designing for the Future
-- Martin Holladay
I agree that a good roof is critical, as is designing a house with a roof that is simple, with adequate overhangs. "Transitional" homes with multiple tacked-on gables, dormers, and pockets that hold snow are roof leaks waiting to happen. Also important is water management from below. It seems that many houses are built that ignore very basic siting and foundation guidelines that cost very little, if any dollars.
Concrete houses lasts the longest, that's how they do it in Asia, even for the cheapest of the houses.
Thanks for your comments, everyone. I guess I'll approach this in parts.
1) Martin, I've read your articles (at least, the ones I have access to) - I agree that, in certain cases, a green building does not need to be durable. A structure that requires very little resources to create is going to be green almost regardless of how long it lasts. Absolutely. And I absolutely do respect your opinion: your Pretty Good House philosophy has informed my considerations ever since I heard about it. If it weren't for local height restrictions, I'd even be sorely tempted to pursue a 12:12 roof like you recommend.
Under the circumstances, however, I would prefer to build one that is more durable for the following reasons:
a) Resiliency: I want it to easily beat code minimums for disaster resistance; WFCM recommends engineering for a 1-in-700-year gust, and I'd personally like to do better;
b) Comfort: I want to keep it climate controlled, and in an extreme climate that requires either a prodigious waste of energy or a lot of insulation;
c) Space: I would like to have a reasonable amount of space (~2,500 to ~3,000 square feet); and
d) Vanity: It would make me feel good to build something that will outlast me.
Certainly, as you have pointed out before, there are limits to durability. While some houses last for many centuries, it of course involves significant compromises and a great deal of work to make them fit into modern life. Their ongoing survival certainly has more to do with a desire to preserve cultural heritage rather than any questions of sustainability or practicality. Your example, Versailles, is a good one - of course, even if I did have le Roi-Soleil's budget, I probably wouldn't spend it all on a chateau, however grand!
One of my hopes is to attempt to make an educated guess as to how long it would even be *practical* to build a home to last, aside from as a vanity project. Maybe it's possible to build a house to last 200 years. Does it make any sense to do so? How many people are happy to live in an average house from 1817? My part of the world has no examples of this; the local Blackfoot peoples tended towards a nomadic lifestyle. The first European structure built here, Fort Calgary, dates to only 1875 and, by and large, has been lost to time (though it was more recently recreated).
Has anyone done a really in-depth analysis to answer that kind of question? How long does it make sense for a house to last? I wouldn't just count on codes for this - I think that they leave a lot on the table in the service of compromise.
2) As for the folks recommending concrete: Thank you, but I had thought that in the long run there were longevity concerns with residential reinforced concrete construction on account of the tendency of rebar to rust and cause spalling? Certainly non-steel (basalt or GFRP/CFRP) rebar would sidestep the problem, but that costs even more and there's no real prescriptive information available regarding that sort of replacement.
In any case, I'd expect that there would need to be significant advantages in durability and/or energy use in practice to justify the embedded energy in a house's worth of concrete relative to the carbon sequestration in a wood frame. I'd be curious to hear whether anyone has done any analysis on how long these actually tend to last. (Except where deliberately demolished or lost to fire, the majority of the *thoroughly* mediocre stud houses built here after the war still survive in Calgary; concrete would not impress me if it is spalled and cracked into uselessness after 50-75 years.)
I know that there are some real ICF adavocates out there. I get that it can build an impressively strong structure, engineered to resist 300mph winds, small arms fire, aerial bombardment or whatever other unlikely scenario you'd like to throw at it. There's definitely a Three Little Piggies factor in there. No need to fear the Big Bad Wolf.
There is not a doubt in my mind that all but the worst-designed of ICF houses are vastly superior to a code-minimum tract house - but from the looks of it, you can do some seriously good work with wood! That includes on insulation and airtightness.
Extrapolating from the American maps, our 700-year wind gusts are only 115 mph, and I believe the next level up (1-in-1700 years?) was 121 or 122mph. Given that WFCM goes up to 195MPH for Exposure C, there's probably no need for concrete overengineering as you can already make a wood house strong enough to survive anything it's likely to see here short of a direct hit by a tornado - and you're looking at something like 1-in-100,000 year returns on that, and that's erring well on the side of caution. Similarly, 0.2s peak spectral response for seismic here is just shy of 0.2g for a ~2,500 year return period.
My stumbling points involve a) cost, b) embodied energy, c) the thickness of a finished wall section once insulated to R-40 or thereabouts; 6.25-8" of concrete plus 10"+ of insulation, air gap, cladding, interior finishes, d) the difficulty of finding ICF roof and floor assemblies to really take advantage of the benefits of ICF construction (if the roof blows off in a thunderstorm, the house is probably a write-off regardless of whether the walls survive), e) the paucity of prescriptive design information for ICF, f) longevity issues as mentioned above, g) the difficulty of finding contractors to build it, and h) the fact that, as far as I can tell, ICF houses really show their advantages over a well-designed, well-built wood house in increasingly unlikely edge cases (see above).
In this case, I'd love to hear that I'm wrong.
3) I think that my question might have been far too wide-ranging. A better one might have gone like this: is there a practical limit to the lifespan of, in particular, plywood? The truth is that I'm stumping over double diagonal sheathing versus plywood as a diaphragm and shear wall sheathing material. Plywood has some huge structural and practical advantages that I'd hate to leave on the table for no good reason. Getting extra years of lifespan that I won't need is not a good reason.
If you want your concrete to last a thousand years, follow the advice in the attached article ("A Concrete Slab for Y3K").
Martin - that's quite the slab!
The 75 year lifespan cited before the onset of corrosion reinforces my misgivings about concrete. Unless concrete builders can find a happy medium in lifespan between a tract home and the Pantheon, I don't think it's the product for me. If I lived in a hurricane zone, I'd probably change my mind.
Would I be correct in saying, then, that it would be best to build something that meets my needs, won't fall down unexpectedly, and makes respectful use of energy? The owners, myself or anyone else, will maintain it for as long as it's still usable and desirable. Then, it'll be torn down.
I suppose that's better than building an absurd edifice that will last just long enough to become a blight on the landscape.
Q. "So it would be best to build something that meets my needs, won't fall down unexpectedly, and makes respectful use of energy?"
A. Ah, yes -- once again, we come back around to the Pretty Good House.
-- Martin Holladay