Certainly CMU can be used. And can provide a reasonable foundation. I would think that the issue is with the variability in quality you get from the CMU is higher than with a poured foundation, reinforced with rebar.

I may be biased, but we've had poured foundation in our home in NC for years (with a basement) and it's 100% dry and 100% as straight as it was the day it was poured.

I see all those masonry joints, and the hollow block and just don't think it's as high a quality as a well done poured foundation.

I've built both depending on the availability of blocklayers. There's greater uniformity with blocks as they are a consistent manufactured product created under supervision in a climate not subject to the weather. Of course, on-site labour can screw it up by not mixing the mortar correctly or placing rebar where specified etc. Structurally, concrete has greater lateral strength, blocks more compressive strength, according to one of the professional engineers I consulted with.

What I don't understand is the logic of crawl spaces. Go down a few more feet and you have a huge amount of extra living room for very little extra cost.

Or do a slab on grade, save some money and don't worry about damp crawl spaces and the critters which go with it.

Have you looked at ICF for the crawl space and the walls? ICF walls might be less expensive than 2x6 walls.

I just got an email from a builder today. He doesn't do crawl spaces, and as I'm waffling between ICF and 2x6s (with 1" of XPS), he wrote, "ICF is less expensive than stick built due to higher demand for wood products caused by a strong economy and recent hurricanes."

The guy's based on Washington State's Olympic Peninsula, too, where I'd guess trees outnumber people by about a billion to one.

As for alternative foundations, regional custom drives a lot. The shallow frost line here makes a basement much more expensive and flat lot makes it dark. Slab is considered cheap around here and only acceptable for townhouses. I am not going to single handedly change that perception and my feet are hurting in my slab rental townhouse right now. Then there is where to put the ducts - the townhouse has to use attic for the second floor. Then you have to foam the roof line and getting high R value with that is expensive. Takes away the entire slab savings.

ICF is rare around here and 2x6 with 24 O.C. is likely a lot cheaper. That being said, with the lumber issues - it is worth looking into. Sound is important to us so ICF would help there. But I am guessing, since it isn't done often around here, there will be a big premium.

The savings with CMU is about $10k on a $600k build.

Are you in a rated seismic zone? If so, everything from foundation to roof will have to meet the increased requirements for lateral loads and special connections of all assemblies to one another.

Every single place below the 18” footing requirement depth does slab as the majority foundation of their builds because it is the less expensive way to go. Even 10M houses of all the stars in Brentwood do slab on grade. It’s not considered “cheap” by anyone. It’s considered standard construction for a warm area.

Almost no one foams the roof line. Only an upper end build would do that. Yes, it’s a better choice, and the price is going down. But almost no one does it. The majority do vented soffits and ridge vents, with insulated attic floors.

Basements and crawl space are very rare because the required footing depth is so shallow. And the further south you go, the higher the water table. Which means wet crawl spaces or basements.

When you get to a certain point south, just above or around sea level, pier and beam becomes more common as a means to get the home up above the moisture of the high water table, and potential coastal storm surge. That high crawl space is not a basement, or even usable as habitable space. Patios, garages, workshops, sometimes. It depends on the height above flood elevation needed, and the skill of the architect to not make it look like it’s sitting on popsicle sticks. But this is recaptured space. Think of it as a ground level basement.

Perhaps if you won’t consider slab as helpful to your budget, you would consider pier and beam, and actually get some useful space under the home.

Because a block stem wall and crawl space is the worst possible choice from both the cost and the structural stability aspect. It’s more labor intensive, and labor is the single biggest expense on any home. It still requires floor joists, which slab does not. Again, a ton more labor intensive construction. Even if you did foam at the roof line, that cost would pale in comparison to all of the increased labor and materials required to create a crawl space.

^^^ agree with the above - but it's hard to overcome that "slab = cheap" mentality of some of the builders and buyers in my local area. As we learn more about indoor air quality, slabs SHOULD become more prevalent, as should keeping all your HVAC in conditioned space, but that's a longer road because electricity and natural gas are cheap - and therefore, little effort goes into that kind of operating cost reduction / energy efficiency activity.

The crawlspace is so icky. LOL - now we're seeing everyone "encapsulate" it - to the tune of tens of thousands of dollars.

agree with the above - but it's hard to overcome that "slab = cheap" mentality of some of the builders and buyers in my local area.

I think the problem with this thinking is that it only holds true holding other things equal. We have that same problem here, that the tract builders moved to slab on grade and people who don't know any better assume that it is a lesser construction product.

However, that perception largely goes away when you consider the use of the savings. Take that savings from slab on grade and invest it in a nice hydronic radiant system, or upgrade other systems. You can do a lot with that much savings.

The crawl space will be sealed and dehumidified.

I wasn't here to debate crawlspace.

Sophie - slabs are absolutely not done here. I suspect there is less than 0.1% of $500k+ houses built on slab in our area - but hey this isn't Brentwood. I understand you are listed as PRO but that doesn't mean you have any idea what my market dictates. "Every single place" is absolutely wrong. It is a resale issue. It is an expansive soil issue. It is a where do we put the duct work issue. All HVAC will be in conditioned space.

I don't believe anywhere in NC is seismic but we certainly are not.

I wasn't here to debate crawlspace.

With respect, this board is about more than simply providing you with an answer. It is about all the other people who may find your question and use the information contained here to make their decision.

So feel free to not engage in a crawlspace debate, that is perfectly fine and reasonable, but please realize that this is the right spot for that debate.

It is a resale issue. It is an expansive soil issue. It is a where do we put the duct work issue. All HVAC will be in conditioned space.

I concur it is a resale issue, but finding the Net Present Value of slab on grade vs. an encapsulated crawl space is still relevant to the discussion. My initial estimate is that a $600,000 house would have to lose more than $100,000 in resale over 10 years to achieve a positive Net Present value.

Which, again, is not a reason for you to do it, but it is a reason that the discussion is relevant.

I don't understand how all HVAC can be in conditioned spaces while also being in the crawlspace. If your runs are in the crawlspace then they are in unconditioned spaces. As for where they would go, floor trusses...

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As for your question... I think CMU would be fine, but then again, I like CMU. Having said that, you probably researched your builder a bit more than you did me, so maybe my advice should be ignored.

"With respect, this board is about more than simply providing you with an answer. It is about all the other people who may find your question and use the information contained here to make their decision."

If only those people providing answers had a code book...or actually understood...

"I don't understand how all HVAC can be in conditioned spaces while also being in the crawlspace. If your runs are in the crawlspace then they are in unconditioned spaces."

A solution that satisfies both energy codes and the desire for a warmish floor that does not feel like concrete...not to mention HVAC

I am not even going to post the whole code, because I think most people already understand the basic principle. You can follow the links and read it yourself.

https://codes.iccsafe.org/public/document/code/553/9809187

https://codes.iccsafe.org/public/document/code/553/9849024

Is that really considered conditioned?

@jannicone - If you read the entirety of both sections, you should have your answer.

Sophie Wheeler - "Almost no one foams the roof line. Only an upper end build would do that. Yes, it’s a better choice, and the price is going down. But almost no one does it. The majority do vented soffits and ridge vents, with insulated attic floors."

This is very interesting. I think our roof is spec'd for foam and we've been getting feedback that it's expensive (upwards of $20k more in some bids). Needless to say we are cutting that.

We're building on slab. Slab is actually more common in more expensive builds than crawlspace, here. It's interesting how things differ, region to region.

So you either have to 1) condition that space (hello larger HVAC) or - you have to pull air from your living space and exhaust it out though the crawlspace (which again drives more demand on your HVAC). I would call that semi-conditioned. I didn't see the space clearly defined in the links. Thanks.

I guess the part that is not so obvious is that new energy codes require tightly built houses and then a whole house mechanical ventilation system to push stale air out of the house, and pull fresh air in... regardless of whether there is a crawlspace.

2.1 works in conjunction with the whole house ventilation by heating the crawl space with the stale air that is required to be removed anyway.

2.2 is a more conventional, "in the box" approach where the fresh makeup air for the whole house ventilation can be "tempered" in this space before going into habitable spaces. (This would assume a clean, dry crawl space.)

Both can be considered a cheaper alternative to a HRV/ERV in a moderate climate...and, the ductwork does not need to be insulated.

Sorry if I'm breaking the OP's rule by diverging from the topic, but conditioned crawls are not something all that new. Building America, informed by the work of Dr. Lstiburek of Building Science Corp., has been touting them for more than a decade.

Thanks for the clarification! It's starting to get really complicated for a crawlspace!

If only those people providing answers had a code book...or actually understood...

"I don't understand how all HVAC can be in conditioned spaces while also being in the crawlspace. If your runs are in the crawlspace then they are in unconditioned spaces."

A solution that satisfies both energy codes and the desire for a warmish floor that does not feel like concrete...not to mention HVAC

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Can you please point to one spot where I said that I said that HVAC should be in a conditioned space even or one time when I said that there were no alternate solutions? I simply asked a question....

Now when you have done that please find the part in the code that disallows slab on grade foundations.

When you fail to do either of those things maybe you should put down your code book and join the rest of us in a discussion on your check book....

actually the OP was specific that the crawl would be sealed - unless my reading comprehension is worse than I thought.

"Can you please point to one spot where I said that I said that HVAC should be in a conditioned space even or one time when I said that there were no alternate solutions?" - Maybe you had better concentrate on your own reading comprehension. Nobody said you did. It can simply be advantageous. But, that defense surely does not explain this statement; "I don't understand how all HVAC can be in conditioned spaces while also being in the crawlspace." I was simply answering the unasked question, not trying to get your hackles up. "It is about all the other people who may find your question and use the information contained here to make their decision.", but apparently, you are the only one who can use that worn out line.

"I simply asked a question...." -A question has a (?) at the end of it. "If your runs are in the crawlspace then they are in unconditioned spaces." Is not a question, or necessarily correct.

"Now when you have done that please find the part in the code that disallows slab on grade foundations." - A completely incompetent and irrelevant defense that only a child would argue. Nobody said that it could not be a slab foundation. You may as well ask where it says you can not have gravel in concrete.

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"join the rest of us in a discussion on your check book..." - OK - "My initial estimate is that a $600,000 house would have to lose more than $100,000 in resale over 10 years to achieve a positive Net Present value." - Are you SERIOUSLY suggesting that the difference in cost between one type of foundation or the other is going to be ANYWHERE in the neighborhood of 16% of the total value of the house??? And what does 10 years or 1 year really have to do with it? And don't give me the leveraging the difference in the stock market bull. You have already been shut down on that recently. Most people are not willing to bet all-in with their primary place of residence on when the next market crash will occur. Don't know how you would make your money increase tenfold in ten years to $100k in the market anyway. (A place where you can see that kind of return on your investment every year is something I think we would all be interested in hearing about.) Or that housing prices will skyrocket abnormally. Or whatever other off the wall theory you came up with. Your math seems to be going haywire on you.

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agree with the above - but it's hard to overcome that "slab = cheap" mentality of some of the builders and buyers in my local area.

Well here in FL all homes are built slab on grade or on pier and beam. Whether it's a tract home or a $10,000,000 home on the water.

"Almost no one foams the roof line. Only an upper end build would do that. Yes, it’s a better choice, and the price is going down. But almost no one does it.

Our builder does it as standard. Not sure what tract houses here in FL do though.

There is no point it spending money on something that gives no value to your home.

Crawlspaces are worthless. Unless there is a specific NEED for them due to flooding, I wouldn't have one. It's literally throwing money into a hole in the ground.

Basement. Slab. That's it.

I foam my entire cathedral ceiling any time it gets opened up, but that's the only way to get a good r value with our construction (which wasn't my choice). I would rather have fiberglass due to fire concerns.

And don't give me the leveraging the difference in the stock market bull. You have already been shut down on that recently. Most people are not willing to bet all-in with their primary place of residence on when the next market crash will occur.

It's too late to respond to most of your post, I may get to it tomorrow but I do want to take some time and respond to this.

Even though this has nothing to do with leverage, I haven't been "shut down on that recently." Just because I chose not to acknowledge a post based on feelings rather than facts doesn't mean someone else wins. This misunderstanding of risk is very common, if you let movies and fiction inform your opinions you can misunderstand the equity market and its risks.

For the last 90 years the stock market has only been down two times over a 5 year period. Many people talk about the 2007 and 2008 market crash yet the largest 5 year loss that occurred was 5%, and the largest 3 year loss was 11%. In other words if you invested in the market at the worst possible time, 3 years later you would have lost 11% of your money. The market did have some big falls but they were preceded and followed by big gains. Largely the market collapse just wiped out 4 years of gains.

Since several years prior to the Securities and Exchange Act of 1934 created the stock market as we know it today. The VERY WORST the market has done over a 5 year period was a loss of 5.75 cents on the dollar. That was for those unfortunate people who invested in 1969 and withstood the market collapse of 1974. Of course, had those people waited one more year they would have seen the market rebound and been up to $1.36 on the dollar.

So just to spell this out for those who really don't want to listen. A properly diversified portfolio has not lost money over seven years, and only lost 5.75% over five years. That means that at its worst the stock market always returns at least 94.25% of EVERY DOLLAR YOU INVEST so long as you are willing to wait 5 years.

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On the other hand, houses constantly lose money over 5 years. In fact, they lose money over 3 years, 5 years, 10 years, and 20 years.

The risks of you spending more money on a home than you receive are many thousands of times worse than the risk of you losing money on the stock market. The amounts that are lost on homes are also much higher.

Let's look at a $100,000 home with a 30 year mortgage at 4% interest, a 6% realtor fee and a $2,000 for loan origination, appraisal fee, and closing costs (a pretty low number).

We put $20,000 down to get an $82,000 mortgage (no PMI), we make 60 payments of $391, and have a remaining balance after 5 years of $74,167. Our total cash outlay will be $43,460, so we need clear $117,627 after realtor fees just to break even, which means to sell for $125,135 to break even on a home, assuming the house needed ZERO maintenance, repairs, blinds, painting, plumbing work, light fixtures, light bulbs, etc.

Paying cash doesn't get you off the hook either. You still have to make up your transaction fees and all of your maintenance fees and other non-transferable items and improvements. Not to mention most people can't diversify. There is relatively little long term risk in the housing market but the individual risk is still very high, because you can't spread maintenance risk out.

Houses are bigger risks than the market, actually many thousands of times more risky than the market. Americans have lost hundreds of billions more on houses than they have in the stock market (I suspect it is far more than even that), yet people still insist that houses are safer investments than the stock market.

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I know this has nothing to do with this thread and I am sorry for the drift. I would love to be able to laugh at people who think like this, but I get despondent about the absolute celebration of deliberate ignorance.

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The thread was about the cost benefit of two types of foundations, some felt that you should consider the cost benefit of three types of foundations. I didn't comment on that, I just commented that resale can't be considered solely on its effect later, you have to consider both the costs and the benefits of the foundation type but also the opportunity costs of the foundation type.

Before anyone looks at how the foundation will "cheapen their house at resale," they must also consider what can be achieved with that extra money if you are going to use resale as a criteria.

Personally, I generally don't like slab on grade and would avoid it because I don't like it. Were I forced to use it I would want sleepers installed and would only use it on a 1 story home, never a two story. But that decision wouldn't be driven by resale, I just don't like walking on it and value unfinished spaces above or below finished spaces.

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ETA:

A question has a (?) at the end of it

Does an interrogative need a question mark? For example, "I want someone to tell me why I need a question mark." is an invitation to provide information, so an interrogative which is the proper name for a question, but doesn't require a question mark. You obviously took my saying, "I don't understand how all HVAC can be in conditioned spaces while also being in the crawlspace" as an interrogative because you noted, "I was simply answering the unasked question."

Are you SERIOUSLY suggesting that the difference in cost between one type of foundation or the other is going to be ANYWHERE in the neighborhood of 16% of the total value of the house??? And what does 10 years or 1 year really have to do with it?

I used Net Present Value and a guestimate based on quotes in my area for sealed crawlspace vs. basement vs. slab. I have thoroughly addressed why Net Present Value is appropriate and is an accepted differential evaluation method (in fact, it is the only accepted differential evaluation method). Feel free to have that argument with the world if you want, I am going to bow out of that one. However, if you don't accept that money today is more valuable than money 10 years from now, can I borrow a thousand dollars from you, I will give it back in 10 years?

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The original question was a cost benefit analysis and you found the first opportunity to pull out your code book. You had nothing substantive to add to the discussion. You deserve recognition for your expertise on building codes, but the building code largely establishes what can be done, not what should be done. It is insufficient for answering either legal or financial questions.

Slabs are the 'cheapest' way to build a house on flat land. That's why allot of GC's use that method to increase their profits but charge as if it were built with crawl space. Yes, I do know this as a 'fact'. That's why allot of track builders use this method.

It is a good point that my CMU question has limited applicability to the world compared to the great crawlspace debate. And the resale vs stock market is a good point also.

Here is the crawlspace point that I can't get past. Ducts in conditioned space can run in 3 places in a 2 story house - between floors, foamed attic, or conditioned sealed crawl. Between floors is an obvious choice although it does cost money and raises the height of the building a bit - and stairs. Foaming the attic costs the most money and increases the surface area of the conditioned space the most. It is also hard to get high R values here - ie it costs a lot of money. Our plans have R 79 in the attic plane - how much would that cost with our roof? And arguably you would need to go to R100 since the surface area is larger to have the same loss.

So then you have the crawl space. The cost of which has to be balanced with the super foamed attic in which it will compare favorably. There is also the extra cost of electrical and plumbing in a slab. I am going to guess that is pretty minimal but not zero. The crawl also gives room for the air handler.

Now I do realize there are 3 other options for ducts.

1. Run both between floors. I don't get to design my own HVAC and I have little faith that any of them will be able to manage it but I could ask.

2. Build a chase for ducts just above ceiling plane and blow cellulose on top.

3. Ductless minis. The aesthetics won't work with the family. They could be built into small attic enclosures. Then there is the maintenance issue and also the unconventional aspect of it all. And the cost which is not zero.

There is the hard floor feel of a slab. There is the moisture through a slab onto hardwood floors. There are the potential cracks of a slab (minor I am sure). There is the radon through a slab - possibly no different than a crawl but harder to mitigate later. I suspect $500 solves the radon. I am guessing that I could put open web trusses right on a slab and solve the duct issue and floor hardness issue.

How much would a slab save me? We do have a height requirement which the slab would help with. Our buildable area is 5-6 feet elevated over the road so the "look" is not really an issue. We do have to deal with expansive soils so I suspect the savings is not as much as FL, TX and gulf areas in between. I am open minded with concerns....

I am guessing that I could put open web trusses right on a slab and solve the duct issue and floor hardness issue.

If you are seriously considering a slab, I would use sleepers on the slab, and use open web trusses between the floors. Sleepers eliminate the hard floor problem and I like open web trusses for various reasons, mostly plumbing, but also hvac.

Here are sleepers...

I am actually not opposed to ductwork in attics and crawl spaces. Again, it isn't about which is better it is about the marginal savings of hvac in conditioned space vs. the initial cost of getting it there, and it rarely ever returns the investment.

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For myself I just like crawling through a crawlspace and attic for various things. I am constantly doing something requires access under or over a floor. So I am not trying to push you to a slab, but I am trying to push you to fully exploring all your options.

I always find the regional differences in building practices and value impressions to be fascinating. Obviously some of that is warranted in terms of climate/soil/topology differences, but much of it seems to be purely cultural. I would have thought that would change given the increasing monocultureness of the world, but for whatever reason it seems to have held in many areas of homebuilding.

freeoscar - I so agree. Homebuilding is so conservative.

Bry911 - thanks for the pic. That is sort of what I figured.

Did anyone ever bother answering the actual question?

I couldn't find it.

If it hasn't been answered, I would opine that you are fine to do the foundation with CMU. You're correct, poured concrete is better for a number of reasons. On the other hand, CMU is adequate and I think you've judged correctly that the upgrade to poured concrete isn't worth it in your specific use.

As I pointed out earlier, either PIP concrete or CMUs will work for stem walls. But if the OP is in a seismic or high wind zone, it's likely that special design requirements exist.

poured concrete is better for a number of reasons.

And what would those be?

Having seen virtually every on-site ready mix operator attempting to water down the pour for "ease" of moving the concrete around and often not doing slump tests and not vibrating, I have some scepticism about the superiority of poured anything. Then there was the '90s case in Eastern Ontario where, after a 16 month trial and appeal, a concrete supplier and ready mix firm were found to have poured 139 foundations that had to be replaced.

I intend to use a motorized dolly to navigate our crawl space; I think it would be fun.

Op literally wants to throw his money into a hole in the ground with no prospect of return. Lol.

The OP originally wrote, "...I get that poured concrete is "better" but what does better really get me in practical terms?.."

If you are really concerned, why don't you have a structural engineer come out to your property and make recommendations?

Poured walls are cheaper then CPU.

Is CPU cheaper than CMU?