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Misc... thoughts/questions about foundations

Post in 'DIY and General non-hearth advice' started by wg_bent, May 8, 2007.

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  1. wg_bent

    wg_bent Minister of Fire

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    My wife (notice not me) is pondering the idea of an addition on the back of our house. I like doing that kind of work, although I'm somewhat slow I feel I do work that's as good or better than many contractors.

    the Addition would be about 15x25 two story.

    The questions:

    1. I could certainly find out from a block company, but more fun to engage you guys. How much does a cinderblock cost?
    2. Is it worth it to build a cinderblock foundation myself?
    3. Do they have to be filled with concrete?
    4. Is a precast foundation wall cheaper? I know it certainly is a lot quicker, and guaranteed for like 30 years.
    5. Can a precast be mated to an existing cinderblock foundation?
    6. How hard is a cinderblock foundation to build... really. I calculated about 420 cinderblocks. Seems like a lot of concrete mixing then building, then mixing then building....

    Obviously I've never built a foundation wall before, but I've done some framing including a recent basement remodel.
    the interesting part of the precast walls is that I could order them so that they would be both the foundation wall and the first floor wall combined, assuming it's a crawl space or better yet, just a slab floor.

    Ideally, though, I'd be happier with a basement under this since the house currently has one 15x22 basement room now that is finished, and no other basement space for things like my workshop. And just think... this addition would be a nice opportunity to add a wood heat appliance... possibly something like a Quad 5700 or a wood furnace in the basement, running duct work up into the house. Investigation phase for the time being...

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  2. elkimmeg

    elkimmeg Guest

    Warren liunch break for me now But I promise to address your questions are you talking 8" 10" or 12" blocks plus you still need a decent footing

    How tall will the foundation be? what is your existing foundating poured or block. Are you planning to do the block work yourself? do you have a lot of time on your hands and lots of pipe staging and planking. Are planning on hand mixing premixed bags?
  3. wg_bent

    wg_bent Minister of Fire

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    I believe standard blocks are 8x16 correct? Yes, a footing is required. Tall, either tall enough to have a crawl space if I hit rock while excavating, or a 8' basement wall if I don't.

    Existing foundation is cinderblock.

    Yes, the plan would be to do the block work myself... unless it's not worth it, and/or the precast is cheap enough to make it not worth my time..

    I'd be doing premix bags I'd guess... no?

    Pipe staging? Time.. well, no it took me 6 months to gut and redo my basement. But I have less money and no time deadline.
  4. HarryBack

    HarryBack New Member

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    there needs to be a concrete footing first.....regardless of the type of foundation. There is no GOOD way to tie new block to old block....old block can be punky, and messing with rebar, trying to anchor it in the old block is likely a lesson in disaster. You can use precast panels....you can use block (most commonly 8"x8"x16")...you can have it formed and poured, you can also get some of those neat styrofoam blocks and have concrete poured inside of them....simple, neat, and fast....saw that once and was quite impressed with the system....works pretty neat...here's a link:


    http://www.quadlock.com/concrete_forms/benefits.htm
  5. wg_bent

    wg_bent Minister of Fire

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    Well, not exactly Harry. The superior walls use a crushed stone footing. I know several people who have houses built with these walls and so far they're happy. With their Xi walls that are R12 plus 6" of insulation, you'd get an R31 wall. not bad. Now, the link you sent looks very interesting since the whole thing is made out of foam and concrete with up to R40, but I assume that's the thickest wall which probably would not be needed in my application. Seems like a 8" wall would be plenty. With the polystyrene, I'm guessing that's about R14 plus 8" of concrete are somewhere around R3 or so for an R17 wall. While that may not sound impressive, I don't believe this precludes adding additional layers of 2x4 with insulation on the inside, plus the wall does not allow for any air infiltration. Reduction of air infiltration is VERY key in the effectiveness of the insulation. It's said in some of the reading I've done that 1" of the expanding foam insulation is better than an R19 wall that is not sealed against air movement.

    Thanks for the link Harry. No local dealers, but interesting none the less. One other thing I've considered is that anything can be built modular and with Chelsea Modular just across the river, I'd have to look at then doing the addition. Two simple boxes with nothing dropped on top of the superior foundation, and I could have my shell up in a matter of days. (How's that for optimism) Then all I'd have to do is the finish work, electrical connections, plumbing and exterior. Hmmm... so many ways to build.... I wonder if my wife would go for a straw bail .... nevermind... there's no way.
  6. elkimmeg

    elkimmeg Guest

    My vote is for a poured 10" concrete foundation or the modular styrofoam poured foundation. I know the national code calls for a concrete footing 20 by 1' thick.
    I have not seen just stone in 20 years and would have to ask for engineering results to pass that setup including compaction test and soil evaluations I would use re rod to pin the poured foundation to the existinf foundation All of which can be formed and poured in a day excluding the prior day footing Let me tell you doing a 7 or 8' high block wall is beyond most home owners.
    To do it right staging is required no way is one going to step ladder one block at a time the cement will set to fast before you get 8 blocks set
    Now a 4' wall eliminates the staging.. Figure it this way form labor is the same for 4' wall as the 8' wall with the exception of pouring labor same setup time.
    The key will be the excavator if he digs a level hole. Also important is creating access for where the cement trucks will pour from. Poured concrete is better for soils that retain water
    or situations that have water problems. I know the blocks can be damp proofed but it is never as good as poured concrete.

    Block walls do take quite a bit of skill and a lot of lifting and labor intensive. The top has to be poured solid to accept anchor bolts. When one thinks about things, sucess begins at the foundation.
    10' poured walls are far superior than blocks. To me trying to do things inexpensive at the foundation level, means compromising the entire process. But again millions shop Wallmart
    cheaping out. When younger I did a few block foundations and bulkheads because I could not get a cement truck to the location. Pumping concrete was not readily available at the time

    Another thing with blocks one can not backfill them till the concrete floor is poured and the first story deck is built and sheathed or backfilling will colapse the block walls.

    You may be very talanted craftsman, but judging from your questions, you have no experience with doing a block foundation. Every block is 40 lbs If mixing alll concrete an laying the blocks your self figure 40 to 50 blocks a 8 hour day Could be as few as 25. Make sure you purchase enough end block and half blocks. Amount of blocks layed will decrease as you take time to tool all the grout joints
  7. wg_bent

    wg_bent Minister of Fire

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    Your right Elk... I have NO experience laying blocks. Framing yes, but blocks no. Given your statements, it sure sounds like the blocks are out.

    I suspected as such. It also doesn't interest me. If I don't enjoy the work some, it won't get done. I don't mind framing and sheetrock etc,,, And I actually enjoy plumbing.
  8. Hogwildz

    Hogwildz Minister of Fire

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    I have the pre cast panels. I lovem. the studs are built in, the holes pre- drilled for wiring, and yes they sit on a crushed stone perimeter. Goes up lighting fast compared to block, and does not crack like block. I do not know the cost as they were up and house built before I bought the place. Every cinder block wall I ve ever seen cracks somewhere. depending on the water table around your place, it may or may not be a problem.
    My barn has same panels, the critters dug the stone away here and there, the beauty is, the walls are bolted together & sealed at the seams. Where the critters dug the stone doesn't sag due to the panels being fastened to each other. I just filled in the stone again and wallah.
    decisions, decisions. Good luck Warren.
  9. Hokerer

    Hokerer Member

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    Before you completely eliminate the block option, check out "dry stack surface bonded". Much simpler for the DIYer and supposedly stronger than traditional grouted/mortared block walls. Something like...

    http://www.thenaturalhome.com/drystackblock.htm
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