Marrying a 12" block wall to 8"

tiogacounty · #21 02/15/10, 06:53 PM

Quote:

Originally Posted by cfabe

If you are building under code your 10' tall wall will probably need to be engineered. It may require 12" block and it may also require an interior brace wall depending on how long it is. If you don't have codes there, you really need to get a very good handle on how strong that wall needs to be by actually doing the calculations. Most how-to books I've seen don't actually get into how to do the load calculations necessary to size building components, they just give some general rules of thumb with the disclaimer "consult local codes."

Absolutely! Now that we are covered by the IRC code, block walls over 4' high are no longer cost effective, due to the massive amount of reinforcing required, as compared to a poured wall. That said, as a builder, I wouldn't even think of attempting a 10' tall block wall if the fill exceeded more than five foot or so. Way too much rebar (vert & horizontal), core filling, and inspection headaches to bother with. I have supervised on projects that exceeded 1/2 million sq. feet with hundreds of thousands of blocks laid, and in cases like that MOST of the block is above grade and sitting on a poured wall. No matter how user friendly it appears to be, block is vastly inferior to poured wall construction, and you are well past the outer limits of standard practice at that height and fill depth. Eight inch block is not used in this area for anything over a crawl space wall height (4') anymore. Over the last two decades I have seen several "builders" end up with massive problems attempting to do eight inch block walls, 8' high with 7' of backfill. Driving by a new home, after a hard rain, and seeing 40' of 8" block wall laying on the basement slab, as the home sags and cracks, is not something you soon forget. I lost a job to a "competitor" once, but still maintained a friendly relationship with the homeowners. The builder did a 54' ranch with a full 8" block foundation. He backfilled with the existing heavy clay soil to a height of 7'. Once the spring rains hit, one of the 54' walls collapsed, and the house needed emergency stabilization to keep it from collapsing into the hole. The builder went under and the buyer had to borrow an additional $17,000 from the bank to salvage their home. Building a proper 10" block foundation, with support pilasters on the long walls, would of been a few hundred more, and saved the builder's business and the buyers a year of litigation and heartache.....and a bigger mortgage.

Sparticle · #22 02/15/10, 07:47 PM

I don't have any long unsupported walls. From what I've read you want a pilaster every 18', but to be safe I've designed one for the center of the longest stretch of 14' just to be careful. The rest of the back and side walls are broken up by thick interior sheer walls which also act as thermal mass and roof support.

We are having someone look over the roof design and engineer it for us.

We are paying for this without a mortgage so though a poured wall might be better, it's far more expensive (we've had estimates - they are really high). That's why we were really wanting to do slip form, but after studying everything I could find on it for several years, decided we just have to pay a little more to get the walls up in time to have the floors time to cure this summer.

We have no building codes so we're being very careful and trying to learn every thing we can, asking lots of questions