This is my first post here, and I registered primarily to inquire about a 2009 article I just read on the main website. I am a licensed civil/structural engineer in Texas.
I just read the article linked in the original post, and was struck by this statement: “Wood foundations are simpler, quicker and cheaper to construct than masonry foundations. They will not, however, last as long as masonry foundations and are less durable in the long-term.”
From Permanent Wood Foundations - InterNACHI http://www.nachi.org/permanent-wood-foundations.htm#ixzz1msfJgOAX
No citation is offered for that claim. More importantly, there are no qualifications on the statement - no mention of proper construction - nothing. I have never found a study that reaches this conclusion. I’ve also seen masonry foundations fail after a short time, and I know that some PWF’s have been around for decades with no indication whatever of degradation.
Was this statement made “from the hip?” Do the authors, or anyone for that matter, have solid research (as opposed to anecdotes or “common sense”) to back this rather general claim? I would very much like to know.
Even your post supports our contention. You said in your post
implying that it is your experience that only a percentage of PWFs have been around for decades with no indication of degradation and that you have only found “some.”
IMHO the article does show some bias against wood foundations.
To improve it you should include examples of failed wood foundations systems and the cause of the failure.
My contention is that the statement is unsupported by citation or solid evidence, and that it is unqualified - only a blanket statement of A > B. This is like saying that airplanes last longer than cars, or that apples taste better than bananas.
Do the authors have any expertise in the matter that would justify them making such a blanket claim? Have they published on the topic in peer-reviewed journals, or have they conducted a meta-analysis of such articles? Even if they did, their statement still lacks what seem to be necessary qualifications.
Allow me to clarify that I do not believe that I have the evidence to support the claim the authors of the article have, nor do I know how one would rightly support or generally refute such a general claim (as would be the airplanes > cars statement). I do, however, have the expertise to point out the simple flaws in such a claim, and as it is a statement of general fact, only a single counter-example is required to debunk it.
Among its problems is that the statement lacks a mention of construction context. For example, I’d wager that, in expansive clays, given a common design, a wood foundation would outlast a masonry foundation, given the elastic range of the former, and the brittle nature of the latter.
You did it again. You supported our contention that on average, masonry foundations last longer then PWFs by pointing to a freak example where there might be an exception to the rule.
The contention in the article is not “on average, masonry foundations last longer then PWFs” but, “They will not, however, last as long as masonry foundations and are less durable in the long-term.” My statement that there are easily conceivable circumstances (expansive clays are hardly a “freak” circumstance) serves to falsify your claim, not to support it, as would a single incidence of any PWF outlasting any masonry foundation. The claim itself is that problematic.
A less problematic claim would be, “on average, masonry foundations built per code have lasted longer than PWF’s built per code.” While lacking the specificity needed to be a useful statement, it could at least conceivably be true.
But, my real question, and I am repeating myself here, is, do you have any actual solid evidence to support your very general, and authoritative-sounding, claim? Can you point to real research, or established engineering facts? Failing that, do you have any solid evidence to make your revised claim quoted at the top here? Is there ANY claim regarding the relative durability of masonry foundations vs PWF’s for which you have good (as opposed to informal and anecdotal) evidence?
I, as a practicing structural engineer, with design and inspection experience in both types of foundations, would not dare make the claim you have, nor its opposite, or even one much more qualified. IF I had solid research evidence to support it, I could conceivably make a claim such as: “Evaluating masonry foundations built between the years of x and x, when compared to PWF’s built during the same period, with both being constructed strictly per minimum IRC xxxx, supporting similar structures, it has been found that the masonry foundations have, by a significant margin, experienced less degradation per the metrics of xxx (water intrusion, cracking finishes, structural failure, etc.).”
I would need real evidence to responsibly make that claim. My hunches would not do. The impressions of associate inspectors or even engineers would not suffice. Selected photographs of failed PWF’s and standing masonry foundations would not influence me. Failing my understanding of reliable evidence to support it, I would be making a claim outside of my realm of professional expertise, and that would be irresponsible, and therefore unethical.
What I could safely say, however, is that a PWF can be designed and constructed, for significantly less money, that will outperform and last just as long or longer than, a masonry foundation built per minimum current IRC code, in many common design circumstances. That knowledge is within my area of expertise, and is supported by established engineering theory and empirical data. I’d never say that PWF’s generally WILL outlast masonry foundations, as there are too many variables for that claim to make sense.
So, again: do you have evidence to back what appears to me to be an overly general and absolute claim, or can you revise the claim to be much more specific, and provide reliable evidence for that revised claim? I would very much appreciate being informed of that evidence.
Oh. Yes, everything is “on average.” We are not saying that every masonry foundation will last longer than every PWF. At your suggestion we added the words “on average” to the statement at issue. Thanks!
You’re welcome, of course, but what is the evidence for the revised claim? Is there any reliable basis for it? And, as it is a fact that a properly designed and constructed PWF can last for hundreds of years, and easily much longer, and that the effective lifespan of a single family home is well under 100 years, should the claim even be promulgated?
The way the statement reads now, it is most certainly true. It’s an uphill climb to argue that something made of wood will last longer (on average) than something made of concrete.
What evidence do you have to support your claims? Where did “effective lifespan of a single family home is well under 100 years” come from? Around 15-20% of the homes I have inspected have been more than 100 years old. Many are more than 150 years old and a significant number of them are 200 years old.
The neighborhood in which I lived as a youngster probably has a couple of thousand homes that are 100 years old and older. I spent most of my electrical apprenticeship wiring homes in the area.
The area I am speaking of, incidentally, is the site of America’s first Civil War (1835-1836).
I’m sorry about the delayed response, George, but I didn’t receive an email notification of your post. The numbers I threw out were conceptual, and not based on actual data. My point was that if a structure with a “service life” of x years lasts 3x years built of one material, or 3.5x years built of another, is it proper to authoritatively claim that one material is superior to the other in that type of construction? Especially if the 3.5x material is, say, twice as expensive?
But, there’s a lot more to this issue than that hypothetical question.
When I gave the “lifespans” I did, I had in mind what is called the “service life” or in some contexts, the “design life” of structures, and I was multiplying the textbook “service life” several times. Again, depending on the context, “service life” can mean two things:
The duration the structure can be expected to serve its original purpose, with reasonable maintenance (eg painting and gutter cleaning), before it is no longer structurally sound and requires expensive (relative to the structure and ordinary maintenance) repair, rehabilitation, or reconstruction.
The anticipated economic life of a structure, in the context of shifting and altering infrastructure. Most structures are actually demolished before their useful service life has ended, because the original structure no longer suits the economic need within the same space. We tear down perfectly serviceable buildings all the time to replace them with something else, to serve another purpose. Because of this fact, we generally do not design residences or bridges or commercial buildings to last 500 years. Almost nothing is designed for that service lifespan.
But, this certainly does not mean that a properly designed and constructed building necessarily will not last that long, especially with above-average attention to maintenance and preventative care, as you cite with your Civil War era homes. But if we design and build homes to reliably last 200 years, with the expectation of the “usual” maintenance and upkeep only (no expensive reconstruction) then these structures will be too expensive for the market. In the business, the service life of a house is about 50 years.
I personally live in a house built in 1950. I know intimately every bit of the structure. Except for a few elements, the house was built quite well, and certainly above average for its day. But since I moved in about 6 years ago, I’ve had to take “extraordinary” measures to extend its serviceable life - things that very few people would ever do to their own homes. I intend for this house to be able to last another 50 years without further “extraordinary” measures. But in 50 years? Well, the masonry will need at least a thorough repointing. That is not typical maintenance but it will certainly be required to keep the house serviceable.
Now, back to Nick Gromicko’s article, which makes the empirical claim that, “On average, they (PWF’s) will not, however, last as long as masonry foundations and are less durable in the long-term.”
When I challenged Mr. Gromicko to produce evidence to support that claim, his response was simply, “It’s an uphill climb to argue that something made of wood will last longer (on average) than something made of concrete.”
This just won’t cut it. And because the average home-buyer will look to an authoritative-sounding source such as InterNACHI as a reliable source of information regarding residential structures, and more so because home inspectors will look to InterNACHI for information that they will pass on to their clients and associates, InterNACHI needs to meet a high standard of evidence for its claims. In this case, it has failed to meet any standard at all, and is making a claim based purely on a vague notion.
What does actual research say about the durability of structures built of different materials? I direct you to the following, excerpted from the article at the link below:
Historically, many building industry professionals believed
that use of materials perceived as more ‘durable,’ such as
steel and concrete, would result in buildings with longer
service lives than wood buildings.
However, a survey of buildings demolished between
2000 and 2003 in the Minneapolis/St. Paul area
demonstrated that there is no significant relationship
between the structural system used and the actual life of
the building. Reasons for demolition were instead related
to changing land values, lack of suitability of the building
for current needs, and lack of maintenance of various
non-structural components. In fact, the survey found that
developers demolish most buildings well before the end of
the useful life of their structural framing.
Wood buildings in the study had the longest life spans.
Sixty-three percent of the demolished wood buildings were
older than 50 years at demolition and the majority were older
than 75. By comparison, over half of the demolished concrete
buildings fell into the 26-50 year category and only one third
of the concrete buildings lasted more than 50 years. Similarly,
80 percent of the steel buildings demolished fell below the
50-year mark, and half of those were no older than 25 years.*
Moreover, when speaking of residential foundation construction types, it is very inaccurate to imply flatly that one is made of “wood” and the other “concrete.” A proper PWF is no more made of just “wood” than a proper concrete foundation is made of just portland cement, water, and aggregate. The two details (incomplete as they are) that accompany Gromicko’s article make that clear. It seems that, in the only argument Mr. Gromicko offers in support of his claim, he has in mind taking a lump of concrete, and piece of untreated 2x4, sticking them both in the dirt, and betting on which one lasts longer.
I’ll add, to further strengthen my claim that the notion of “something made of concrete last longer than something made of wood,” is of no use, this:
As I pointed out, “concrete foundations” are not just made of concrete, just as PWF’s are not just made of wood. The typical 8 or 10" concrete wall is pretty useless without the reinforcing steel inside it. Concrete foundation walls are just as much made of rebar as they are of concrete. So here’s a mental exercise: Take a piece of no. 4 rebar, and an uncut Southern Pine 2x4, CAC treated to a level of 0.15 pcf. (or if you cut it, soak the cut end in preservative) Drop them on the ground and walk away. Which one lasts longer? The wood, of course.
So, from that notion I conclude that things made of wood last longer than things made with rebar. What, not fair? Did I leave something out?
The concrete grade beam on my 1950 home (and many others) was approaching failure. The concrete was spalling along the rebar lines, and the rebar was exposed. What happened? Well, the house went a long time without gutters, and the rain splashing on the ground next to the grade beam would hit the concrete, soak through the concrete (which probably has a fairly low cement content) and reach the rebar. Between the water and oxygen in the air, the rebar was expanding (it will expand more than 200% when corroding) and blowing off the concrete cover. Before too long, the steel was going to corrode enough that the beam was no longer going to resist bending sufficiently, and fail. I had to do pretty extensive repairs.
Meanwhile, the untreated 2x4 sill plate, sitting right on top of the concrete grade beam, is in excellent condition. Why? Because very little, if any, water ever got to it, and there is an effective termite shield in place. Therefore, I say that wood lasts longer than reinforced concrete. What? Is that an unjustified claim?
Nope, you are wrong. Stay focused on foundation types (the topic of the article), not building types or materials in very unique, hypothetical situations. The following is from the study you quote from:
That study you quote doesn’t compare buildings that were demolished because of foundation failure. The following is taken from your study:
In other words, you posted the results of a study that on the surface sounds like it might have data germane to this discussion, but in fact does not. The study you would need to post would be one of buildings that were NOT demolished due to “*changing land values, lack of suitability of the building for current needs, and lack of maintenance of various non-structural components” *but rather buildings demolished specifically due to foundation failure, for us to compare the percentage of those buildings that were demolished specifically because of PWF foundation failures vs. the percentage of those buildings that were demolished specifically because of masonry foundation failures.
A study that shows that most fruit is eaten before it rots, doesn’t provide useful data to help us determine if apples rot faster than oranges rot.
Futhermore my article does not determine why most buildings are demolished and doesn’t contend that most buildings are demolished due to foundation problems.
And even furthermore the study you quote from is talking about building types, not foundation types.
And finally, I am not convinced that the authors of the study you quoted from are referring to solely PWFs when they use the term “wood building” as wood buildings on masonry foundations are typically referred to as “wood buildings.”
While your points about the article I quoted are correct, I did not intend them to indicate that PWF’s last as long as, or longer than, concrete or block foundations. What the article shows, is that your only argument in support of your claim that concrete or block foundations last longer than PWF’s (even with the qualifier, “on average”), which was “it’s an uphill climb to argue that something made of wood lasts as long as something made of concrete,” is inadequate.
Further, I showed that of two adjacent structural foundation elements, grade beams and sill plates, the wood sill plates were exhibiting greater durability. I also showed that heavily treated wood lasts longer than exposed rebar, which is an essential part of a concrete or block basement wall.
What I am doing is showing that the only evidence you’ve offered so far, the notion above about concrete lasting longer that wood, is inadequate. You may be able to find research supporting your claim that, on average, concrete foundations HAVE outlasted PWF’s, but without that, you don’t have a leg to stand on.
But even if you do find that research, it may also be a problem that the earliest PWF’s weren’t built to nearly the standard of modern PWF’s. In that case, without a qualification indicating the superiority of more recently-constructed PWF’s, you are giving them an unfair shake.
In addition, your claim does not address an important question: what kind of timescale are you talking about? Will a properly constructed PWF perform well for the expected service life of a home? What is that service life? Do you mean that a concrete basement will last 500 years, and that a PWF will last only 300? Would that be relevant information to inspectors or homeowners?
In short, I believe you should either remove the statement because it is completely unsubstantiated, or you should find real research backing up your statement, and include any qualifications necessary to fairly represent the durability of PWF’s vs. reinforced concrete or cmu’s.