Foundation Help

[diamond]

I am going to be building a house,and I would someone to tell me the pro's and con's of what type of foundation to use.....[e.g. slab or footer and block}. I live in East Tennessee and it will be about 30'x30'. Don

[mysticokra]

I prefer footings. You have so many more options for changing things later on. When you pour a slab you discover quickly where the phrase "poured in concrete" came from.

We bought a house once where they "forgot" to plumb the slab before they poured it. Now there's an expensive fix.

[Slamfire]

Have you considered a basement, or is it too rocky where you are building. It costs a lot, but not as much as a barn or workshop or etc.... George Carlin had it right you'll soon fill your house up with "stuff".

[Pat]

I agree that a basement can be a good thing, if done right for your soil, water, and any other special considerations. Too much rock will drive up the price like crazy. I prefer and am presently buillding a house with a walkout basement (south wall of basement is not dirt covered and land slopes away from walkout side of basement.)

Best foundation is like how long is a roll of string or how high is up. Answer is, it depends. If you have no problems with expansive soil (expands and shrinks significantly with changes in moisture content) and the load bearing capacity of the soil after leveling the pad is sufficient, then you have several alternatives.

For a smaller home, 30x30, assuming single floor, no basement, stick construction not cast concrete, ICF or other heavy wall methods, then options are still open. Nothing wrong with a combination footer/slab AKA slab with thickened edges. You can trench out deeper under the perimeter and under interior load bearing walls and pour a monolithic slab/foundation. I'd go deaper in the footer portion than the frost line.

You want to use rebar in the footers and under the load bearing walls (where you thickened the slab). You put vertical rebar in the footers which is bent over into the floor. I recomend bending rebar to "run" around all corners in the thickened section under load bearing walls interior and exterior.

Do level the botom of the footer trench and the top of the slab. A water level is cheap and as accurate as a $1000 laser system. Do use oversized chases (plastic tubing /sleeves) for all in/under slab wiring and plumbing. This will help reduce the "set in concrete" problem. If you use flexible PEX tubing for our plumbing runs and replacement should ever be required, it is not that hard to pull out a secton and slide in a new one if the over sized sleeves were put in with no kinks prior to pouring concrete.

Do not be afraid to put electrical runs in the slab if your inspection authorities allow it. This is faster and easier than boring a jillion holes in the studs to run wires. It will not replace all through the wall wiring but an be a useful technique. Oversize the conduit for any electrical runs under the slab. I say under rather than in because a large conduit in a thin slab will weaken it. You can trench a little grove to run the conduit under the slab. Pay attention to glueing the conduit as if it were water line so water will not get into the conduit. Some folks have used direct buriel cable without conduit but that is a risk I wouldn't take as replacing a run, as unlikely as it is, would be virtually impossible. You could run direct buriel wire in your plastic conduit if there was concern that water might get into the conduit.

Slab-on-grade with thickened perimeter and under load bearing interior walls, if any, is likely the most and best for the $ if it is suitable for your situation. I personally prefer a raised wooden floor with exposed plumbing etc. in a crawl space but it is more expensive and less durable and just plays to my personal preferences not because it is better. Raised floor with crawl space allows ease of retrofit but if you do your attic right, any retrofit can be done there. What can I say? We did my mom's new hoiuse with raised floor/crawl space and my house-in-construction has a slab floor in the walkout basement, slab floor throughout the ground floor and slab floor above master suite in the upstairs. Of course gagage and shop are slab. Only floors in upstairs space not above master suite is other than concrete.

A slab floor is undoubtedly the most cost effective in most cases where there aren't any special circumstances. NOTE: if you have subterranean termites in your area, do not forget to have the dirt treated shortly before pouring the concrete. Night before is good enough but don't delay pour too long after treatment. There will always be some small amount of cracking, easily ocntrolled by rebar and not a structural conlsideration, that can admit those wood destroying devils, (termites).

Other considerations for a slab would be vapor barrier (plastic sheet) very carefully taped to all penetrations for plumbing etc. This will prevent radon and unwanted moisture from coming through the slab. It is also a good idea to put insulaltion under the slab in the form of rigid 4x8 sheets or thermal blankets of aluminized bubble wrap. This makes a significant difference in your winter floor temps and can lower heating costs. It is good to continue the underslab insulation under the footing and out a few feet to provide a thermal break between the slab and the outside dirt. This insulallton will pay for itself in savings in costs to heat if you buy natural gas, propane, oil, coal, or use a heat pump. If you chop wood and consider your time, effort, or back important, then the underslab insulaltion with extension under the foundation and out a few feet is still a great idea.

Best of luck to you as you proceed in the house building adventure.

Pat

[slowzuki]

Very complete post Pat. I am also a slab fan. A lot of people in my area are very attached to the idea of basements but I can't see any use for them. It is much cheaper to build a bigger garage if you need the storage.

My simple explanation to people is, if you want to collect water, what do you do? Dig a hole in the ground.

It is hard to get things into and out of, damp, source of large heat loss etc etc.

Now a lot of this is rectified by having a walkout and insulating below and around before pouring, but then you have stairs in your house.

[Pat]

slowzuki, We started out at my wife's request to not have stairs and have all floors on the same level. Now, with her complete agreement and cooperation, we are building three floors; ground, basement, and upper floor (mostly attic space with partially sloping ceilings with dormers to make more livable.) the upper floor is slightly split level with two steps to get from "main" upper floor/loft to the shop upstairs above MY SHOP.

If properly done, basements are not damp. If a walkout, not dark. There are simple measures, not too expensive (some real cheap) that virtually guarantee a dry basement floor even if there is a leak in the wall.

I elected to insulate under my basement slab and to insulate walls that are dirt covered. I didn't build a basement for storage space. You said it, storage is cheaper on the surface. My basement will have a mechanical room for some of the HVAC equipment, water heater, etc. It will also have a kitchenette, a full bath, bedroom/saferoom, and a "game" room (pool table and card table for bored/board games.

A concession I made to aging was to design both stairways (to basement and to upper floor) as straight runs with ample landings at both ends and 4 ft wide. This will permit, if needed in the future, the retrofit of an electric operated "stairchair" that will take you up and down the stairs. These are available either with a chair to sit on or a platform to take a wheelchair. They are really reasonbly priced, way cheaper than any of the elevator or vertical lift handicap assistance devices. The stairs, at 4' in width will accomodate either form of the stairlift and not interfere with normal use of the stairs.

The ground water table at our basement site varies a bit but gets as near the surface as 5 ft or less. This would have made an indoor swimming pool of the basement had I not taken appropriate measures. The French drains have been draining continuously since last December as we approach the 1 year mark since breaking ground. I expect they will drain forever. I didn't test the water but suspect it to be essentially as good as local well water. It just runs into a pond.

A conventional basement is super cheap to heat/cool even without insulation but insulalting the outside of the walls and under the slab will still pay off. I used InsulDrain rigid insulation which also ensures that no water stands against the wall. If I bored a hole in my basement wall it woulldn't leak as there is no water in contact with the wall. It runs through chanels in the insulaltion to the French drain.

Pat