I’ve been watching a tear down here in Chicago. They took the old house down last week and dug the trenches for the foundation of the new house. The first 18 inches or so was topsoil and the rest was 100% yellow sand. Will the typical 4′ foundation walls work when built on top of sand? The old house was a 120 year old frame 1.5 story, built on a slab, standing straight and true. The new house will be a 4 level concrete block fortress.
I’m not in the business, just curious about these type of things. Thanks for indulging me, if you choose to do so.
Replies
yes, sand is the perfer subgrade material around here. we build 98% of everything on sand. First thing I tell the contractor, sand, sand and more sand.
But arnt you building slab on grade?
I dont know squat about either but wouldnt there be a difference?
Doug
I,m sorry I dont understand the question
we build 98% of everything on sand
You said this back in your initial post in this thread.
I was asking you if your building slab on grade.
I didnt know that putting a 4' footing in sand would be OK, it sounds to me like your saying it is a good idea. I would have thought different but I really dont know, thats really what I was asking.
Doug
Doug, bb is not the OP, Rich is.
alot of what we place are "on grade" but also, our frost line requirements are only 18 inches. We do not have basements. never saw one around here. as far as bearing pressure on sand. it not that much lower than a clay. basically 2200 psi, so the footing are not that different. If you do go into pure sand you will have to form the footing but if you stop the sand at footing grade and then your fill above that is a sandy base then it will work with a dirt form.
Thanks
I didnt know that putting a footing on sand would be OK, I dont do this kind of work so I was just wondering.
Doug
Yes, sand works well as long as it has nowhere to escape to from under the foundation. Sand won't swell and shrink like clay soils will in the presence of water.
Sand does work since it drains well. The down side to sand is that it doesn't hold a lot of weight per square foot so the footers have to be sized apropriately.
Beer was created so carpenters wouldn't rule the world.
Don's answer was best. One simply neds to design ooters wide enough to support the loads of what will be bbuilt on it.
Think in this way-
A woman in heel heels will create a force of thousands of pounds per square inch on those stillettos and damage a lot of wood floors. A child wearing moon boots distributes weight over a far larger surfae, so the force is less and no penetration to the surface underneathe.
Correspondingly, a three story structure built on narrow piers is likely to settle while a one story structure on a wide foting or a slab will disperse that weight of a wider surface and not settle.
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