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jbref002
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# Posted: 26 Aug 2018 05:27am
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I bought a property about 2 years ago that has an existing 40x60 slab that was never build on. I plan on building a 24x24ish cabin this spring. As I assemble my plans I am trying to decide the best way to build on the slab, the slab is level and in excellent shape. I am deterred from building directly on the concrete due to the heat loss, and sweating during weather changes. I thought about using Cinder Blocks, pavers and those square foundation blocks designed for building on. These are all great idea's but none provide enough elevation to get a body under to repair plumbing if needed. Does anyone have any other idea's for building on top an existing slab?
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Princelake
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# Posted: 26 Aug 2018 08:25am
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If it's like a garage slab they did footings and poured around 4" of concrete. Being 40x60 and cabin 24x24 your not going to really completely land on a footing. I'd lay out my cabin chip up where your going to put your footings and pour your own footing it into the pad. Put rebar in to tie it in and put vertical rebar and build up as high as you would like to go with cinder blocks.
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toyota_mdt_tech
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# Posted: 26 Aug 2018 10:44am
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Or ignore the slab, but your cabin somewhere close to it, convert the slab to a large covered carport or shop or even part shop, part carport or build cabin at end of slab, then make a large detached garage with a nice concrete covered section between it and the cabin. Nice place to hang out on rainy days and still BBQ
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Borrego
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# Posted: 26 Aug 2018 01:45pm
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Quoting: toyota_mdt_tech ignore the slab, but your cabin somewhere close to it, convert the slab to a large covered carport or shop or even part shop, part carport
Great idea! Since you want a raised foundation anyway it doesn't make any difference if you use the slab or not. You could use a corner of the slab and have the rest be covered outdoor area, but you'll want to pour new spot footings anyway.....
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ICC
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# Posted: 26 Aug 2018 05:18pm - Edited by: ICC
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One thing about foundations like that is how can you be certain it was done right? How deep are the footings, how wide? Not everything that somebody builds is done right. Is this slab a monolith pour or is there evidence of a perimeter stem wall pour with an infill slab done later. Are there concreted in place bolts around the perimeter?
You can answer that question about footing depth, more or less, by picking a random spot and digging a hole down beside the edge. Concrete should go down as far as the frost depth in your area. If you tend to be cautious like I am, you would do that in two places. If you are in a warm climate, no or little frost, the footing should be 12 inches deep.
If that shows the perimeter is of proper depth then you can check the likely width of the footing by drilling a few holes. Recommended footing widths vary but a single story on grade slab should have a 12 inch wide footing everywhere. Footings for a two or three story would be wider. So I'd drill a hole about 14 - 15 inches in from the edge and one at about 10 inches in. The drill hole 10" in from the edge should have deep concrete while the other will likely only have 4 to 6 inches of concrete. Maybe do that in at least one other spot. A good hammer drill and concrete bit makes that drilling job easier than digging the hole to check the depth of footing. You could drill to check depth too but need a long long bit.
If you go ahead and build a smaller footprint building you should cut out a footing width of slab and dig down the required depth for a proper size footing. You can rent a concrete saw. Lots of work and lots of water needed for the cutting.
Even if I decided to use the slab for a workshop or barn I'd want to know the footing depth and the slab thickness.
A slab makes a great foundation when the footings are properly deep. A much more stable foundation than anything on piers, unless the piers are concrete block and on a full perimeter poured concrete footer.
Nowadays the right way includes a layer of foam under the slab for insulation. That makes for a warm floor in winter.
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jbref002
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# Posted: 27 Aug 2018 06:14am
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I really want to stay away from putting in piers, And really like the idea of using the slab for a cabin. 4 inchs of settled concrete should easily support a 24x24 building on blocks.
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neckless
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# Posted: 27 Aug 2018 11:02am
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most people on this site would give tooth and nail for a start like that lol
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Savern
Member
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# Posted: 27 Aug 2018 07:51pm
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Build cribbing blocks. (Google for pictures)
- build as high as required
- build as many as required
- 18" X 18" or 24"X 24" will give you a large loading area
- use pressure treated lumber for first row
- place a moisture barrier between concrete/ground and block
- place sheet metal between block and building
- overhand sheet metal so critters can not get to the building
- can be shimmed for any settling
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