Pipe sleeve and under ground conduits through foundation : how big is too big?
I am building a slab foundation, with 4’6″ frost walls and 24″X8″ footings. The front corners of the house and garage are about 20 feet apart. I would like to sleeve the foundation walls so I can run conduits between the buildings, for future services. The questions:
(1) Ideally I want to run 3 separate 2.5″ conduits between the building. As such, a 6″ PVC sleeve through the 8″ wall will not do. I will need an 8″ sleeve. Is that too big for an 8″ poured concrete wall with no rebar? Are there rules that determine how far up it has to be from the footing?
(2) Ideally I would like to run my water line through this sleeve (I would like to avoid digging under the footing for the water line). This means that at the wall it would be about 3.5′ down, and my frost line is 4′. Is there an equivalent insulation I can wrap the pipe with to compensate for the missing 6″ of soil cover?
(3) In the even that insulation is not possible, what is the best way to get the water line into the house? The footings are being poured on “undisturbed” soil, so I hesitate to trench in the footprint. If I have too, how deep to i go below the footing? Do I sleeve the pipe (2 sizes larger)? Do I backfill with compacted gravel?
(4) Is there a grade of conduit I should ask for? I want to make sure I can run everything underground between the buildings (natural gas lines, electrical, water, hot water for heat in insulated pipes, ethernet, cable etc).
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Replies
1. Sleeves that size are very common, especially on the bottom 1/3rd of the wall.
2. Try to avoid going through the wall with the water line. The soil below it will settle and put shear stress on the water line. If you need to go that route install 4" of 25psi foam 6' wide over the line.
3. You should install your water line about 6" or more below the footing and mark it's location so the concrete workers don't spear it with a form pin. You can hand dig through the footing area to minimize the disturbed area, but I wouldn't lose much sleep over it. Sewer and water are typically installed into the house footprint before wall trenches are dug, meaning there is usually a 4-5' wide disturbed area. It's never an issue. Tell the concrete guys to install some rebar in that location.
4. Conduit is cheap. Schedule 40 is most common, but I like the extra strength of schedule 80 for a small price increase.
Thanks Rick.
I was worried about the grade of conduit, after reading a horror story on the web about a guy who did exactly what I am planning, only to find out his conduit was not rated for electrical!
Is there a rule of thumb as to how much concrete I should leave between the top of the footing and the 8" PVC sleeve?