I have to sub out a CMU Block wall. Not the usual 5-8 job, just a knee wall, about 40″ or so, with no fill or weight behind it. Just a dumb block wall. Because it is under 48″ no permit is required. What should the footing size be.
Code here for a 6 foot wall is 18″ wide and 24″ deep, but I suppose I could get away with less, since it is only 40 inches high.
Ideas?
Boris
“Sir, I may be drunk, but you’re crazy, and I’ll be sober tomorrow” — WC Fields, “Its a Gift” 1934
Replies
A lot depends on the soils type and frost depth, and drainage.
Excellence is its own reward!
10" high... 16" wide, but the bottom has to be below frost line
natch... it also has to be on good bearing soil... and the whole thing should be designed to bear the load
Mike Smith Rhode Island : Design / Build / Repair / Restore
where you are makes a differance.. when the ground freezes it expands then in the spring with soft ground you basically have a sway back issue.. while concrete seems very hard in strength it is rather fragile.. (there is a reason bridges made out of concrete have all that steel in them.. )
If you are in the freezing portion of the country go below frost or plan on frequent replacement.. perhaps not every year but often enough that you won't like it..
my walls of my house are 8 feet tall cmu filled with concrete, the gable ends are 14 feet tall fill with concrete to peak of ridge. They weigh about 1100 lbs per lineral foot that a half of a ton. On a forty foot wall. 20 tons.
It depends on soil condition, as a soil engineer tech, I calculated total weight. i have no frost line, it might get to 45 degree for couple days during winter. Soil is red sand clay with a bearing ratio of 2500-3000 lbs
My footing are 18 inches wide by 12 inch deep with 3 #5 rebar. no cracking, no settling, no problem
But it depends on the soil
This "dumb" block wall of yours - is it just a fence type thing or are you going to top it with some kind of structure?
For frame construction on a 5 course CMU stem wall my footing is 20" wide by 10" deep and 12" into undisturbed earth. No frost here. Three #5 bars in the footing and sticking up every 4' as well as 2 in each corner. After the wall is up, the top course being lintel block, one #5 is placed in the top course and the vertical bars are tied to that with another #5 with a 2' lap on the top bar and a bend into the cells containing the verticals and wire tied top and bottom. Inspector has to see the second bar tied to the bottom of the embedded verticals through knockout blocks in the first course. Then all the cells are pumped.
For total CMU construction the footing and the steel is the same except all windows and doors also get a #5 on each side and only the cells with the steel and the top two courses get pumped full.
My latest footing under a frame addition was a mono pour footing at 16" wide by 12" tall with a stem wall formed on top of that at 8" wide by 12" tall. 2 #5's in the bottom and 1 #5 in the middle of the stem section.
Probably more info than you really wanted to know, right??<G>
Sorry guys, I live in California so there is no frost issue. Forgot about frost, and that people actually live somewhere else. And yes, just a dumb block wall, a fence; not a retaining wall, not a foundation; just a dumb fence.
Regards,
Boris
"Sir, I may be drunk, but you're crazy, and I'll be sober tomorrow" -- WC Fields, "Its a Gift" 1934
Edited 8/5/2003 12:08:06 PM ET by Boris Yeltsin