I’ve got to put a footing and block foundation under an existing two-sided, two story addition (9×5) to an old house for a bathroom. (The bathroom is existing. The foundation is essentially not.) The foundation for the main part of the house is mortared limestone block. The sill is about 4′ above grade. The existing foundation is frame on dirt. Termites, of course. Took the floor joists, too.
Anyway, does anyone think there would be any great disadvantage to just pouring concrete inside the crawl space for a floor? It sure would make it easier to work in there to replumb the bathroom, which will be gutted and remodeled.
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I'd say prepare the surface by digging out some more dirt, give it a little sand and a layer of black poly for moisture, then go ahead and pour your slab. You'll be working in tight quarters, and a perfect finish isn't necessary, so you might want to do it in sections to keep the size down to a day's work each.
The advantages are that you now have clean dry working conditions for everything else you want to do down there. And you have a clean hard surface to crawl on, or even roll stuff around on using a flat dolly. That sure beats dragging things through the dirt. Given that you have 4 feet of headroom, make a nice big access, and it can be a convenient place to store ladders, rakes, gardening equipment, etc.
The only disadvantage I can see is that you make more work for yourself if you ever need to get access to the ground under the house. You might need that if you remodel and have to put in a new footing for a bearing wall, as I did. You might want to put a ground rod in the basement if you change the electrical service. Those tasks would require cutting/breaking the concrete.
But IMHO the advantage of being out of the dirt for the rest of what you want to do far outweighs those disadvantages.
-- J.S.
In Chicago we call it a mud slab. 2" of concrete on gravel with poly under the concrete. Rough towel finish.
In my area we call it a "rat slab".....it could be called an "anti-rat slab" but for some of us, that's harder to say.
I've persuaded the HO's of the last 3 houses I've built to put a slab in the crawlspace and they've ALL been grateful for it.
The cost is minor against the long-term benefit.
Thanks Notch, Archy, and John. I tend to agree that the advantages outweigh the disadvantages. Another disadvantage I see is if there is a leak in the plumbing, that water becomes trapped in there. The access hole from the main basement into this crawl space is above the level where the slab would be. So, it could become a well in the case of a major leak. I suppose I could put a piece of conduit through the block at top of slab level for a drain and slope the slab that way. And yes, the main waste line goes down through that space. The concrete would pose a considerable problem if that had to be dug up. I'll have to ponder it some more.
Thanks all for your feedback.
If water gets in there, being able to pump it out sure beats having wet dirt and mud that you have to wait and wait for to dry out. As for the buried sewer line, you could form up to leave say an 18" wide strip open above it. Then you could cover that strip with stepping stones that could be easily lifted out if need be.
-- J.S.
Good ideas, John. Of course, if I put in the stepping stones as you suggest, any leaked water would soak in there.
These poor people are house broke -- a great big house because it's a romantic notion to buy a big old house -- and I suppose I'll just spread plastic in there and rumple it all up while I redo the plumbing.