Cost Savings Of A Slab Versus Crawl Space

72chevy4x4

I just ran some rough calculations (very rough) comparing the cost for a slab foundation versus a crawl space; in your experience, have the savings of a slab been significant? First floor space is roughly 2400 sqft. Is a 4" pour acceptable for one large unbroken slab for a home? It seems coordination and planning w/ plumbing and electrical is important as well as placement of hvac systems-am I missing anything?

osborn

Monolithi8c pour.

Bob Kovacs

Well, considering you're eliminating an entire floor framing system, as well as up to 3' of foundation wall height and replacing it all with a concrete slab that you'd likely be pouring in the crawlspace anyway, yes- I'd say you can expect a fairly substantial savings.

What would make you think it wouldn't be?

Bob

concretemasonry

Nothing is cheaper than slab on grade.

But, it is not the most common for practical and other economic reasons in the end.

You have not hit on insulation and comfort to mention the obvious.

Also, 4" is not structurally sound.

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Dick

Engineer, designer and consultant recently active domestically and internationally on construction and design in about 35 countries.

mdshunk

Would you mind ellaborating on that a little bit? Are you talking about the mechanicals and interior framing fastening?

house bldr

It really depends on code in your area.If you can pour monolithic it can be a cost saver but if you have to pour footings and then stem walls,all you lack of having a crawl space is excavating the middle. Around here we don't pour a floor in the crawl space, so the price of the concrete would be applied toward the floor joists and sub floor.Also most plumbing and hvac bids will be less in a crawl than having to dig it all in before the pour!BUT IMO unless you live in an area with ground water problems a basement is a good way to double your square footage without all that much extra cost,more bang for the buck!I would never build one without a basement if I had a choice.

concretemasonry

mdshunk -

house bldr just answered all your questions for me.

No question about the value of a basement if you are facing going down for frost requirements. It is the cheapest area (construction and heating) you can get.

Also, terrain will dictate. If you have sloping lots, both crawl spaces and basements are cheaper in the end if you consider everything.

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Dick

Engineer, designer and consultant recently active domestically and internationally on construction and design in about 35 countries.

joasis

Hard estimating costs spell out 20% reduction by slab on grade. And we run a 4 inch floor, period, with no problems. More concrete does not neccessarily mean better, I will stand on engineering principles and quality of work.

I think in the future, we will see more concern with insulation a slab, or rather, isolating it. When I was talking with the spray foam guys, something they were saying will be coming is the shooting of grade with 1 inch of closed cell foam and pouring concrete on it....now my first thought is BS!....but the psi rating of the foam opposed to the actual weight of the concrete works out.

I too think a basement is the best value, but they are not that common here, and few buyers even ask....but for my money, I would do them in ICF's.

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mdshunk

They pour slabs over foam board in my neck of the woods all the time.

72chevy4x4

I was looking into ICF's-$5,000-$6,000 would get enough to do a 2000 sqft basement-works well for rectangles, but the many cuts of a house I'm looking at, I'm concerned about cave in's-there would be 12 corners in all with 9' walls.

we have water table issues in my neck of the woods-I'm sure good drainage could remedy that.

with the concrete over foam referred to-is that the same as pouring the outside walls, then isolating the inner slab and placing foam board down before the pour? What is the R-value of the thick foam board versus the closed cell you are referring too? Spraying foam hasn't caught on here-I was looking at hiring a guy two states away to drive over and spray an entire house worth of foam-I love the idea but it has a high price tag.

TimNJ

You not only want to put foam under the slab, but also around the perimeter as a thermal break between the slab and the foundation wall. Otherwise the cold will transfer right in from the outside of the foundation.

thom

All my houses are slab on grade, and generally 2 story.

I do footing - stem - slab. Makes a better job than a monolithic, though both are common around here. Underground plumbing goes in after the stems and isn't a problem, but around here that's the way it's done so the plumbers know what they are doing.

Stem has a step in the top. It's a 6" stem with a double 2X4 blocked to the inside of the form creating a 3" X 3-1/2" step in the top of the stem. 1" styrene is placed in the step and down the inside of the stem to the footing. This isolates the outside of the stem from the slab to diminish heat loss.

4" is plenty strong, in fact much stronger than a framed floor. You don't get a whole lot of deflection in a slab. Bearing locations without stems are handled by thickening the slab, generally over an area about 18" wide, to 12" thick, with 2 @ #4 rebars in the thickened area. This creates a foundation for interior bearing walls that adds nothing but a little material for the concrete sub.

Basements are rare around here. Our footings are only 16" below grade.

We stucco the exteriors with the stucco extending down over the foundation to below grade. There is no unsightly concrete below the siding. An added benefit is that the sill plate joint is closed/sealed so there is no air infiltration.