sbc concrete block foundation/walls - question

[siggers]

I was wondering if anyone could explian a couple things about sbc block walls. I am planning to build my basment from a stacked block wall.

Can someone tell me typically on a full basement for a 20 x 24 using 8" block what the size of the footer would be.
Does the first course normally use a 12" or 8" block?
And does the final top course need to use a different type of block, that is filled, prior to the bottom plate attatching.

Thanks in advance.

[glenn-k]

I don't know about for block, but our basement project has a 24"w x 12" deep footing all around for 8" concrete walls 8 to 10 feet high.  Most of the concrete block walls I work around are grouted solid with rebar in them anyway.  Usually an engineer designs the walls and reinforcement.

[JRR]

Typically there is 8" (min) footing width on each side of foundation wall ... this would agree with Glenn's 24".  But check with your local authorities.  My county had a hand-out that listed all such foundation requirements.

An 8" wall usually starts off with an 8" first-run course.

The top of the wall can be finished several ways.  I usually run the top row "up-side down", then I poke a cut-to-fit welded wire screen about half down the top block.  This then gets a filling of rather dry mortar.  This I do on all cores that don't get filled from ground-up with anchor rod and concrete fill.

There are also special cap blocks available.  I never use them anymore.

[n74tg]

I am building my house with drystack (and SBC) foundation walls.  One of the Taunton Press "For Pro's by Pro's" books (Working With Concrete I think) discusses footer dimensions based on soil compressive strength.  If on hard rock your footer can be same width as wall thickness and is used basically/only to provide you a level, constant elevation surface on which to lay your block.  Contrast that with building on uncompacted sand (think of the beach) where footer width needs to be three times the wall thickness to spread the load out adequately.  My case is compacted soil (compacted here means not previously dug in) with some rock (shale), so book says two times wall thickness is adequate.  For me (8" block) that would be a 16" footer, but most of mine are 17"-18" in width with minimum thickness of 8" and three runs of rebar.  

If you plan to build a two story house (read that as footers having to spread out more load), plan accordingly.  I won't give any numbers because I don't remember them.  

If you're interested, my blog, below chronicles the adventure and has more detail than above.

P.S. I live out in the county, so I get to decide what to build and how to build it; ie no inspectors.  If you have to live with inspectors, then they get to say what is minimum required.   Good luck.

[jraabe]

Most building departments assume a 2000 psf bearing soil and then call out a 15" x 7" or 16" x 8" poured footer with 2 #4 rebar 3" up and in from each outside bottom corner. This is good for a 2 story house with either a poured or block wall. You also need to pin that wall to the footing with either a poured key or rebar pins tying up into the vertical bars.

If the soil is soft or the loads are heavier then a wider deeper footing is a good idea. Where entire areas have soft soil, deeper wider footings may be a standard requirement. (24" x 12"?)

If you are on bedrock you can just pin and level the wall to the rock.

A one-story house can have a 6" foundation wall and a 12" x 6" footing under standard conditions.

[JRR]

BTW, its good practice, early on, to lay out the location of the floor joists.  This way you can plan anchor bolt locations that don't coincide with the joists.  Saves a lot of grief later.

[siggers]

Thanks alot guys, I just wanted to make sure I was on track with everything.

n74tg your blog is great, thanks for sharing it.