I am looking at building an addition and need a full foundation. I was think of using 12″ below grade, and 8″ above. If I grout all the cells and use #4 rebar every 4 feet isn’t this as good as an 8″ poured wall?
The form work, the possibility of a blow out and the minimum ready mix delivery makes me want to do block. I have a bag mixer for the grout.
Any other ideas?
Thanks
Allen
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Replies
Going 12" below grade won't work if you live in a frost area.
Telling us where you're located would be a good start towards getting a correct answer.
The work is in Massachusetts. The 12" is the block. I would need to go to 4' including the footing.
I live in Canada we get tempuratures well below 0 deg C. (32deg F)
Using 8" block on a proper footing is allowable for most residential applications here with either a 4' deep foundation or a full 8' basement foundation. No rebar are required in the walls. I have put in many foundations this way with "o" callbacks.
Your question leaves a lot of conjecture. (length of wall, loading, heated or unheated space, etc)
I would check with your local building official with what is acceptable in your location.
The length of the wall will be 12' and 22'. Most of the 22' will be exposed (stem wall underneath. There will be no heat in the basement.
You need to do some research -- 12" block are usually used for the basement, every other course had a length of duro-wire between the courses - no r-bar -- duro-wire is like a ladder am sure you have seen in the lumber yards and goes in the alternate course of the bed joint.
above ground, 4" of the 12" block is used for the joist and the other 8" is used for the 2x4 all and the brick veneer
do some surfing and you' soon see how easy it is to do the wall - forget about filling the cells -- block walls have worked well forever - just need to seal the outside and have footing drains to day light
Compliments to all for great information and kind replies.
The length of the wall will be 12' and 22'. Most of the 22' will be exposed (stem wall underneath. There will be no heat in the basement.
I'm a little confused. I thought you said your walls are 4' tall. Do you have a crawl space or a full basement ?
carpenter in transition
Will be a full basement. I was orginally planning on a stem wall with a full masonry or concrete wall above.
I would suggest that you put some heat in the basement, even if it is the radiant heat from the floor above (uninsulated floor joists). I may be stating the obvious but if you do not provide some heat sourse you stand a chance of structural failure due to freezeing of the surrounding soil.
m
PS I'm not familiar with the term 'stem wall' and therefore may be missing some information regaurding your system of construction.
The downside to block is that it has less inherent water resistance, and less strength laterally.
When the soil freezes, it heaves against the foundation, and can cause it to buckle inwards. Expansive soils like clay can also exert a lot of lateral pressure.
The longer the run of the wall, the more likely this is to happen, since the perpendicular walls add bracing.
I have seen many buckled block walls, but buckled poured walls are rare.
Of course, you can mitigate the risk by building a short 'bracing" wall in the middle of a long run. Your plan for 12" blocks below grade also gives you an advantage.
The likelyhood of buckling is quite small if there is proper drainage on the outside.
BTW, if by "grouting all the cells" you mean filling all the cores with concrete- you may as well just pour a wall, because the advantage of using blocks is essentially gone.
Sounds like you're on the right track but - the very first thing to do is check your local building codes. Just because one method is structurally sound doesn't necessarily mean it meets code. And if you're not familiar w/ all the aggravation and nonsense that goes w/ building codes, you're "fixin to learn" as we say down here. :-) Sometimes they make a lot of sense and other times they just leaving you scratching your head!
I just built our 5000+ sq. ft. 2 story home and we went w/ concrete block over poured walls. (Crawl space - no basement) Cost-wise, they were pretty even but I liked the fact that you can get better accuracy with regards to walls being square and such. Ours was a very complicated footprint and it just made sense. Some might argue otherwise but the overwhelming advice I got was to go w/ block. No regrets yet!
There is no way you will ever build a block wall as strong as a poured re-inforced concrete wall!
but in situations where poured is not a viable option, you can build an acceptable block wall. Here is how I do it -
lay the block with a ladderwythe between courses and a fully grouted rebar all the way in the footing every four feet
Plaster the interior and exterior with a Stck'n'Bond to add strength and water resistance
BTW, I like th 12" below. It resists pressure better. The lateral forces are in balance everywheree you have backfill on both sides of the wall. Also, Make sure you have good perimeter drainage at the footer, and use gravel not clay doil for backfill so no water is retained against the foundation. Clay will hold more water and clay is an expansive soil. It would pretty much gaurantee a failure of a block wall with a baeement
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