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I am planning on adding a spiral staircase to my roof, but after preparing the hole for the concrete foundation, I noticed there is this sprinkler pipe 12 inches under the ground which would be directly under where I would like the foundation to be. Obviously I am worried about the pressure of the staircase/foundation breaking the pipe and causing the ground to sag beneath the foundation. I plan on using about 4" of sand/gravel mix at the bottom of the foundation, and about 8" of concrete above that. The sprinkler pipe (as seen in picture) is about 1/2" wide.

I was thinking about how the options I have to resolve this:

a) re-route sprinkler pipe to go around foundation,

b) increase area of foundation to reduce pressure on pipe (perhaps going from a 1'x1' square to 2'x2' square),

c) encase the pipe in something like a steel cover to protect it from damage.

Option A would be quite challenging, so I was thinking of a combination of option B and C. Does anyone have suggestions as to the best way to tackle this? Appreciate it!

Existing box to hold concrete foundation

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    Option A seems easy to me ...
    – user19565
    Aug 10, 2022 at 18:22
  • Isn't a 1'x1' footer a bit small? I would pour a larger slab so I have not just the footer for the central pillar but also a nice pad as landing-area under the last step of the stairs. Bear in mind that an external spiral staircase is often only attached to the building at the top. Meaning that horizontal load/forces (e.g. wind) may cause over time a small footer to move sideways, especially if the surrounding soil isn't very firm. (It's not the same as footers under a building. There you have multiple footers and a horizontal force that big means you have other things to worry about.)
    – Tonny
    Aug 11, 2022 at 8:36
  • Consider yourself coming along in a few years and find that "someone" has put a foundation over the pipe you need to replace, How mad at them are you for not doing it better?
    – Criggie
    Aug 12, 2022 at 3:34

4 Answers 4

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Dig the hole bigger.

Buy four elbows, some pipe clamps and some extra pipe.

Turn off the water for that pipe.

Cut the pipe and with the elbows have it go around the box.

Make your footing and no worries about the pipe being under the cement.

The pipe is plastic and easy to cut.

Could make do with just two elbows if you make the hole big enough and have a soft bend in the pipe to go around. Like a "U".

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    Yes. Reroute the pipe now before you have a block of concrete and a structure on top of it. My recommendation would be to cut and abandon the existing pipe in place, leaving the soil as undisturbed as possible, since you're pouring a footing.
    – spuck
    Aug 10, 2022 at 18:05
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A pipe rupture beneath the foundation could cause soil subsidence that will destroy your staircase. For that reason I would now route the pipe far from the staircase. Cut it inside the hole you dug, on both sides, remove the inside piece, backfill with soil and compact that. Go about 3 feet away from the foundation in both directions, find the pipe, and trench a semicircle staying 3 feet away from the foundation. Use an elbow at each end to lay a semicircle of pipe. The two disused pieces of old pipe outside the foundation form can be left in place.

I don't know if 3 feet is the right distance, it's a guess ... hopefully someone can verify or correct that.

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    Think three feet would be enough, unless the stream of water was pointed right at the foundation. This is if the leak was not noticed for some time(wet ground, low pressure).
    – crip659
    Aug 9, 2022 at 22:40
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It is not even hard PVC pipe which might be ok.

safest option is (a), reroute.

I had few of those (black hoses) suddenly leaking without reason.

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Does the pipe run in a straight line? If not, perhaps it can be rerouted without needing to cut & join it, but rather just digging a new trench offset to the "shorter" side.

Alternatively, consider running an entirely new line, so that you don't have to manage the risk of underground joints failing. If nothing else, it allows you to document where the line goes. (You may get lucky and be able to recycle the existing line.)

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