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Crawl Space vs. Slab Foundation


I want to write an article about the crawl space vs. slab foundation topic, but I'm having some trouble finding information. Could you tell me the pros and cons of crawl spaces as opposed to slab foundations? 

I'd appreciate any help that you could give!


North Carolina



I think crawl spaces and slab foundations are both evil.

But I'd say that crawl spaces are the lesser of two evils.

In a similar vein, I often rant about the basement versus crawl space debate. Here in Michigan the climate requires foundations as deep as 4 feet below ground, though in some areas the soil is so sandy, so well drained, that slab foundations are allowed. I've seen slab foundations on some really old cottages, some "economy" houses, and on garages.

Quite frankly, you couldn't give me a house built on a slab foundation. With no easy access to any of the "environmental systems" (electrical, plumbing, HVAC) maintaining these structures is a nuisance at best, and a nightmare at worst.

Yet I understand that in some parts of the country, such as most of the Southern states, slab foundations are standard practice.

My girlfriend bought a second house in 2001, a tiny place slapped together in 1958. Technically it has a crawl space, but being only about 2" to 3" high I would equate it with a slab foundation. The wiring and supply piping are all in the attic. Working on wiring is no big deal, it's more of a nuisance because you need to move insulation around to find things. But the plumbing is something else.

Somebody covered up the pipes with insulation to keep them from freezing. Okay, no real problem. So far. Then I discovered that the bathtub drain was not connected. The water was just draining into the soil. Not a big problem, but a source for moisture and all its troubles. I like basements because you can tell right away when something is broken. With both crawl spaces and slabs you probably won't notice quite a few problems, but at least with a crawl space you can fix them.

The overhead pipes make me nervous. I've had plenty of experience with overhead pipes. When I worked in hotel maintenance I saw some unbelievable fiascos when ordinary pipes leaked... pipes that were in the ceiling, above the drywall. Imagine a nice hotel lobby with drywall chunks scattered all over as some fool tries to fix a leak, or imagine paying $175 a night and having the ceiling fall down because some pipe leaked.

Like I say: Pipes Behind Plaster, Recipe For Disaster.

This hotel was about 40 years old. As far as I'm concerned, every pipe is going to leak, especially metal pipes. All metals used in plumbing will corrode with time. Plastic pipes won't, but they have a reputation as being "cheap".

Anyway, imagine owning one of these big fancy new houses with a slab foundation. In 30 to 40 years I can almost guarantee that some pipe in the attic will leak. Nice mess.

Sometimes they put the supply pipes below ground. Oh, great. So when the pipes leak, the water just goes into the soil. And will anybody notice? No. Until the next water bill arrives and it's 100 times the usual amount. Good luck fighting that billing mistake. I can't imagine why anybody would bury a pipe that is on the homeowner's side of the water meter, because any water leakage could go unnoticed for weeks. But they do it.

Builders will say that slab foundations are cheaper. Around here some builders say that building a house on a crawl space saves money compared to a full basement. I don't buy into that argument. It only saves money up front, and almost certainly adds costs later, costs in maintenance and repair.

With a basement or crawl space, many maintenance and repair issues are much simpler than a slab foundation. Even more important, making changes is much easier. If the homeowner wants to build an addition, connecting to existing supply pipes, drain pipes, HVAC ducting, and wiring is much simpler. I don't know about most people, but I prefer a house that allows for some future changes. When it comes to remodeling, I can't imagine trying to work on a slab house. I can imagine charging a lot extra, though.

Another issue that nobody talks about is structural longevity. Long ago I heard a rule-of-thumb for carpentry: keep all wood at least 6 inches above the soil so the splashing water doesn't get on the house and cause decay of the wood. In the Southern states, it's common to build a house on a slab and use stucco over foam insulation as exterior sheathing. The stucco (which is made from cement, not gypsum plaster) extends below the soil, and provides good protection from splashing rain water. But not all slab-foundation homes are built this way.

Around here most houses are plenty high off the ground, but many garages and sheds are built low. And I've seen many of these buildings get structural damage, typically rot but also termite infestations, from rain dripping off the roof, onto the ground, and splashing onto the building. The houses around here with basements usually have 18" to 24" of masonry directly above the soil, and no problem with rotting sill plates. Crawl spaces tend to be lower to the ground, but (from my experience) a lot higher than slab foundations. I have absolutely no confidence in the long-term structural integrity of slab-foundation houses. I have to wonder what all these fancy slab houses will be like in 30 or 40 years. I won't be doing repairs on them, that's for sure. Maybe they'll be knocked down to return the land to farming.

I have a cheaply-built garage that, like many slab houses, is very close to the ground. Well, a squirrel got inside, and the little varmint couldn't get out. It chewed holes in the fiber-board sheathing in at least 20 places! Unbelievable. After it turned the walls into Swiss cheese it made a nest in the attic above the insulated ceiling. The squirrel moved out by its own motivation, but now there are 20 holes that mice find plenty inviting. Now I need to remove the aluminum siding, replace the sheathing with something sturdier and install new siding. At least it's only the garage! No wonder I can't stand the idea of a slab foundation. But this is the type of thing that can happen with a low-slung house, and is very unlikely with a house that sits a good foot-and-a-half above the soil.

I suppose you could look at a slab foundation as an elaborate form of camping... living really close to the ground and all the creepy-crawly critters. I would rather be above all that, thanks.

There is a web site from Texas that shows the steps involved in building a slab-foundation house. There is a lot of really involved work just to bury the pipes in concrete and render them impossible to repair.

Bruce W. Maki, Editor.




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Copyright 2002

Compiled February 21, 2002