How wide of footing for 8” block
loucarabasi
| Posted in Construction Techniques on
Hey Fellas, I am putting an addition onto my garage. Five courses of 8” block, My question is; what are the demensions of the footing? Do I need rebar?and where. I live in NJ. I believe the depth of the footing is 36” at the bottom of the footer. Any help would be appreciated!
Thanks, Lou
Edited 5/4/2007 9:04 pm ET by loucarabasi
Replies
1 1/2 time the size of the wall, so 12 inch minimum
Hey Lou,
Believe you and I have spoken before. Check with the building department, they might require an engineer to seal a drawing. At the least, they could tell you what the depth is.
Kevin
In N.C. depending on the number of stories in structure, the minimum width is 16" wide x 6" and 8" thick for one story and 2 story respectively and 17" wide x 10" thick for 3 story. The minimum footing projection beyond the block face on both sides is 2". The projection tolerance gives the masons room to square up the wall on a 16" wide footing. However, we see most footings enlarged to 24" wide to allow more room to layout the structure and more room to lay block down in the footing when it is 2',3',4' in the ground. Check with your local building inspection dept. they should provide you with the correct info. for your area.
Of course, as always, it depends. ... It depends on the kind of subsoil (i.e. compression strength ...). It depends on how big your garage addition will be. ... probably a few other things...
Having said that, if conditions are "normal", I'd think about 18" wide footing 10" thick (could probably get away with slightly less thickness i.e. 8"). you probably don't need the rebar, but if you go the money, it's a nice to have. I've always put the rebar in during the pour (after inspection). When footings are inspected with re-bar in place, they get mighty picky.
I was taught twice the width, once the depth.
so ... for Pgh, PA ...
8" block?
16" wide and 8" deep.
Jeff
Buck Construction
Artistry In Carpentry
Pittsburgh Pa
local code guys will tell U their rebar requirements.
Jeff
Buck Construction
Artistry In Carpentry
Pittsburgh Pa
Depends on the soil under your walls. Could be from once the width to four times the width. The depth will be 1/2 the width.
SamT
Praise the Corporation, for the Corporations' highest concern is the well being of the public.
The required footing width depends on what your local code says but there is normally a requirement for minimum width and for minimum projection. Projection is how much footing concrete sticks out beyond the foundation wall - both inside and outside the foundation and it might be 2" or 4". Also, minimum footing width and thickness is dependent of the # of stories of the building and the bearing capacity of the soil.
So, if the foundation walls is 8" wide and the minimum width requirement for a 1 story building is 12" in soil that will bear, for example, 2000 PSF, and the minimum projection requirement is 2" then theoretically the footing would only need to be 12" wide.
In the real world, for a footing is formed by simply digging a trench and then placing the required depth of concrete, the footing would never end up in exactly the right place, so trenches are dug wider to give some room for error and still have the proper projection. A 16" or 18" wide trench would be more realistic, and if it is being dug by machine, 20" is a more common bucket width on a back hoe or mini-excavator.
OTOH, my reading here has taught me that methods for "building" footings are highly regional and dependant on the type of soil in the local in question. In some states they form the footings and the process probably takes days to dig and form up in prep for concrete. Granted this method of forming up should save quite a bit of concrete as a function of the precision used to set forms. Since here, we have rather heavy soil, we just dig, get inspection, and pour, which takes hours rather than days - although admittedly we use more concrete than the forming-up method.
The need for rebar depends on the design stipulation, local soil conditions, and local code requirements. I would recommend though that the new footings be pinned to the old by drilling horizontal holes in the old and gluing in rebar dowels.
Edited 5/5/2007 11:02 am ET by Matt