block house foundations

41106

Member
would like to build a new home over the next couple of years. I live in the central part of Michigan so frost is a factor. My question is....I was wondering if there is any way to construct a block foundation one summer including pouring floor with sump/drains, set steel, brace walls, and backfill and then let it set until following summer. This would give me an early start the following year. I obviously don"t want any frost damage. Looking for other opinions and thoughts. Please let me have it!! haha Thank you
 
In central Iowa the frost would get under the unprotected floor and possibally heave and bust your floor. There is alot of frost pressure on those walls with out the deck on top. Just my opinion.
 
When we built our house, we back filled by hand, over several months, a little at a time. Even with all that care, we had several areas of failure. Fortunately my dad had run re-rod both vertically and horizontally in the block wall during construction. Had cut grooves in top of blocks to lay rod in, had it welded, for a continuous rod circling walls on several levels. Dropped rods in vertically, backfilled holes with concrete to secure rods. Threaded tops to bolt sills on. Even with all that care, the wall has structural problems from weight of soil pushing in. Fortunately, rods have held, and failure isn't currently an immediate hazard. I would recommend a plastic skirt tapering away from wall and drainage tile being installed to keep water, and moisture from the wall. That might reduce the weight load and soil pressure on the wall. If I ever have to do a basement wall, I'll consider alternatives to concrete block. And far more re-rod than anyone specifies!
 
I don't see it as much of a problem, some concerns but often times around here, concrete foundations are installed well in advance of framing crews so they can work all winter.

I call block, Concrete Masonry Units or CMU. First priority is obvious, code compliance and all that it entails where you are. If CMU is acceptable, go for it, but be aware of things listed below.

Drainage, both inside the wall and out, on top of the footing, bedded in stone, and covered, wrapped with filter fabric. I've seen open foundations fill with quite a bit of water, then drain out, its amazing how fast it goes down after a heavy rain, likely the most water those drains would ever see.

CMU, would not be my first choice, but reinforced CMU, fully grouted, meaning all the cells of the CMU are filled, every course, or grouted every couple of courses if you can get bulk flowable grout delivered. I don't like hollow cell block for foundations myself, mostly in higher water tables or where water is an issue or always present. CMU is porous, more so than concrete, as the molds they are formed in get age, the surface of the block can have a rougher texture, more voids etc. Waterproofing systems on the exterior of the wall have to be installed properly, and has to be of quality material.

The structural aspect of CMU walls is likely described in local or state building code, to include certain details, some of which may be fully grouted cells every so many feet, same with #4 deformed bar placed vertically and connected to the foundation,(rebar) every so many feet.

You can build a pretty darned strong wall with CMU if reinforced, might be overkill, but I like the cells filled for many reasons, some are waterproofing, fasteners into solid cells are much stronger. I like ladder mesh every other course, you can do it every course, I will include a link to a masonry accessory supplier for reference.

One thing that would concern me is leaving a hollow CMU wall open, allowing water to get in and pond at the bottom course, that could freeze and spall the CMU at the base, fracture and so on, no weep holes. Its just like a masonry parapet wall, without the coping stone on it, will take water and freeze thaw will destroy it over time. Not a big deal, put the sill plates on or what have you to cover it up, another reason I like fully grouted walls.


Mortar used has to be good quality, below grade is no place for substandard material, I'd want a consistent 3000 psi mortar. If mixing your own, you could fill mortar cubes and have your mix design tested, once proven, do not vary the materials or quantities used. We have a big supplier south of here, that provided a consistent bag mix for contractors, though most large outfits use those big hoppers and large bags now, I did recall this supplier in Stormville NY having a very good material in a bag, always tested out fine when cubes were taken on my jobs.

CMU wall may be more labor than concrete, also be sure to coordinate and penetrations, windows, electrical if applicable, easier when the walls are being erected than after.

When purchasing CMU, you can ask the supplier, if they have masonry certifications for the type of CMU you plan to use, any reputable supplier should be able to provide this upon request or they are not legitimate. It tells you that the CMU is of a certain strength.

An interesting fact I believe is that 5000 psi CMU (high strength/75% filled cells-which means cell walls are thicker,holes smaller) is the threshold, beyond that exceeds the limitations that can be consistently achieved by this material and be certified as I was told by Clayton years ago, whom is a large supplier in NJ. I had an engineer specify 6000 psi CMU on a mid rise masonry building, 9 stories, I could not get the certifications and went with 5000 psi, building is still standing. Some of the above may be overkill or not necessary, but having quite a bit of experience in commercial construction, I know how I would do it LOL, check out the link for Clayton as well, all helpful reference information at minimum.
Hohmann Barnard

Clayton
 
I did not even cover backfilling, temp bracing and so on, but Ray did, and thats another reason to consider a reinforced, fully grouted CMU wall. I'd not go near a CMU wall with any fill unless the last courses installed were 28 days old, besides the bracing, and whatever else is needed to stiffen, brace and shore. You can easily blow out a CMU wall, even by filling too many courses with grout at one time, many good reasons to go for the added expense and labor to reinforce, that Hohmann-Barnard site will show you all kinds of accessories including many reinforcing materials.

The thing about masonry is that its modular, you can take your time, get everything laid out, square and all that, have vertical rebar in the footings, use the ladder mesh every course, fully grout each course, though by the time you do all that, its likely your walls will be similar in strength to concrete and a lot stronger than straight up hollow block, might pan out to just do concrete, which I know has become expensive, and you have to pay up front, vs doing masonry, where you can buy what you can afford and install at your leisure. I'd emphasize layout too, it has to be square and the walls plumb, I prefer a wet saw over hand chopped cuts, but thats a preference, and of course the top of wall elevation has to be level and the same, just more to be aware of so you build off a level/square/plumb foundation.
 
I'd be kinda concerned with backfilling too early without weight to help hold it down.
Might also check into a poured concrete walls ?

You used to see many places that did the foundation then put the floor & joists on then made a roof to cover it and lived in the "basement house" as they then finished the upper section over time. I even heard that some made the temporary roof part so it came apart or folded up ? and then made the walls out of it.
Got to be plans out there for this.
 
One note:

DO NOT WELD REBAR

The proper way would be to run it long and tie them together. Welding weakens rebar and does not take much load before it "pops". Sometimes just the cooling of the weld is enough internal stress to crack the weld through.
 
What I would do is spend the summer digging the hole and pouring the footings. Then cover with a thick layer of straw and black plastic (or bury it in sand) and leave it over winter. The next spring, insulate and pour the slab and then use the sytrofoam concrete block molds and additional rebar to pour a solid slab wall. The blocks are supposed to stack like legos and then you just pump in the concrete. The added benefit would be the walls would already be insulated.
 
Ungrouted block foundations are normally fine but there are a few things you need to keep in mind......
NEVER backfill a block foundation until you have the weight of the deck, walls and roof on it.
Let the fill settle. Don't compact it.

I think the approach you asked about is asking for problems.
Water or cave ins damaging the foundation walls.
Frost heaving the foundation or basement floor.
And the liability of leaving an open hole.
In every jurisdiction I know of (and I've been in the construction business 36 years)building permits expire in 6 months or one year.
The longer you drag out a project the more chance you have of someone stealing material.

If you're dead set on building over a couple year period I suggest you use poured walls and don't pour the floor. You could water/damp proof and backfill.
 
Most of the folks here had a lot of valid points. I just built a house in central Michigan and there were a number of things I found out. I didn't want block because I had the same in a house in CT and I think it is too porous. Anything above ground seemed like the air just blew through it. Looked into poured 8" and the code required foam insulation around the whole outside. By the time I added it up the foam block mold system only costs 10% more and left the interior walls ready for drywall and finishing. Very cost effective and warm (code required the drywall over the foam even if you don't intend to finish the basement; $100 extra). One thing we learned was the veins of clay present. Excavating below them adds the risk of hitting ground water.
A neighbor poured a foundation with the intent of finishing the frameing at a later date. Zoning made him build a fence around it as though it was a swimming pool.
If cost is a factor you might want to look into a wood foundation. As far as I know they are approved in, at least, parts of Michigan. A friend of mine went that way and was very happy with it.

Jim
 

I agree with those who warn against back filling without weight on it. Around here it is not unusual to see a foundation with just a deck on it sit for awhile. With the deck on it you could put in some temporary heat for cold stretches.
 
I had a 70 X 100 slab along the michigan Ohio line that sat over winter without a freeze problem by placing a foot of straw over it. Built a house for my Daughter with a poured basement walled walk out 400 yards north of that.(open end)Tile drained the footer as well as under the floor in the fall. Back filled with pee stone. Framed the house starting in the spring. No problems with cracking or out of plumb walls.
 
When I was young there was a guy near us that dug, poured and decked a foundation. He wrapped the deck in tar paper and lived in the basement for several years. He even filled in the grade and put in the lawn. When you drove past all you saw was a black box sticking a foot or so out of the ground. Several years later he finished a brick ranch over the top.
 

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