Best approach for running a pipe through my exterior wall?
June 1, 2015 8:18 AM   Subscribe

I need to run a 1.5” (so about 2” outside diameter) schedule 40 PVC pipe from my sump pump through my exterior wall so that the pump can discharge outside. I can go through the wall or the foundation. What's the better approach?

I have two options—get my mason to drill through the concrete foundation (meaning the pipe would exit probably about a foot off of the ground) OR go through the siding. The catch with going through the siding (cedar shakes) is that I’d have to do some exploration to make sure I don’t do through a stud, joist, or conduit. That is to say, I’d have to cut a hole in the basement ceiling, the first floor subfloor, and then place a hole to the exterior. All of which is doable, but a hassle compared to my mason drilling a hole through the concrete. But having a hole drilled in my foundation makes me squeamish.

Drill through the concrete—which could be done with precision by my mason exactly where I want it and would actually be done, rather than perpetually on the to do list (but would be a hole in my precious foundation!)? Or spend more time myself exploring inside my basement ceiling and in the wall so that I can come out through the cedar shakes (where I have vents for the dryer and makeup air for my furnace already)?

Is drilling though your foundation an inherently bad thing?
posted by Admiral Haddock to Home & Garden (10 answers total)
Go through the concrete. You won't harm anything if you are not using a jack hammer. A hammer drill will make the task a bit ugly, but using a profession masonry drill should yield a clean result.
posted by Midnight Skulker at 8:26 AM on June 1, 2015

I'm having to make a similar decision to run a greywater system. It's harder for me to go through the wood because I'd have to go through some joists, so I'm headed towards the "drill a hole in the foundation".

My reasoning: Drilling a hole in the foundation, as long as you leave enough material above and below the hole, is pretty much the same as puncturing the center of any other beam: Doesn't really impact strength that much as long as you stay clear of the edges.

But other than that my plumber said "oh, yeah, people do this all the time", I haven't done any checking with an engineer on it.
posted by straw at 8:26 AM on June 1, 2015

I would say drilling through the foundation is a lot less inherently bad than going through the wall. If you went through the wall you'd want special framing and finish trim, not just a pipe sticking through cedar shakes. A small perforation of the foundation is not going to weaken it in any way. Seal up around the pipe at both ends with a concrete sealing caulk. If you or someone down the line ever removes the pipe, the hole is easy plugged up with some fresh concrete.
posted by beagle at 8:27 AM on June 1, 2015 [2 favorites]

Filling it with cracks by battering the crap out of it would be a bad thing. Drilling one 40mm hole through it with a diamond hole saw? It won't even notice.
posted by flabdablet at 8:27 AM on June 1, 2015

Another vote for going through the concrete. It should be fine.
posted by amanda at 8:32 AM on June 1, 2015

Go through the concrete, especially if you're having a mason do it. You can run any concerns by him. Since the hole will be above grade it shouldn't contribute to any water leaking in.

And if you're going through the wood between the upstairs floor and basement ceiling, your'talking about drilling through the rim which may present its own structural issues.
posted by bondcliff at 8:54 AM on June 1, 2015

My buddy's dad is a plumber, and he had to make this choice when installing a dryer vent in his daughter's house. He drilled a 4" hole through the foundation with a 2 foot long diamond hole saw that probably cost more than my car.
posted by pocams at 9:28 AM on June 1, 2015

Re the "two foot long diamond saw": Yeah, I do my own feed lines, but let others do my drains. The bid I've gotten for the first stage of the greywater system, a valve in the tub drain just below the P-trap and vent, feeding out of the crawlspace to the outside of the foundation, is $850. A huge portion of which is a subcontractor boring the hole through the foundation.
posted by straw at 10:29 AM on June 1, 2015

You might want more than 1' of rise coming out of your sump pump. If you live in a place where it gets cold enough for standing water to freeze, figure out how much slope you need to get that water out of the pipe, then add 25% or so, just to be sure.
posted by Geckwoistmeinauto at 12:01 PM on June 1, 2015

Structural engineer here. What is the pipe doing once you get outside the house? Will it terminate at the outside edge of the exterior wall, or tie into something? I assume that exiting through the siding would mean a higher drop than through the foundation, i.e. greater than a foot? Don't forget to design for what will happen with the water when the pipe drains - you want to channel the water away from the foundation to a certain degree.

Is there some reason you can't use a stud-finder (or knock with a hammer) to find your wall stud and floor joist placements? These should be simple to locate, and if so, you could select a location for your pipe penetrations that would avoid floor joists and studs (don't forget the bottom plate(s) and any special lateral bracing in your exterior wall, if applicable) without having to create any exploratory holes in your finished basement ceiling. Of course, it's hard to know exactly where any conduit would be and you may prefer the aesthetic of exiting through the foundation.

Drilling a small hole through your reinforced concrete foundation is not an inherently bad thing, but if not done properly, it can be annoying to fix. When drilling a small hole through your reinforced concrete foundation wall, you want to avoid placing the hole too close to the edge of the concrete and avoid hitting rebar. A reinforced concrete foundation wall will typically have steel rebar running in both directions, horizontally and vertically. You'll find your first layer of horizontal reinforcement about 3" down from the top edge of the concrete, and then subsequent layers will be spaced anywhere from 6" to 18" on-center, but usually 12" on-center. Vertical rebar is typically 12" on-center, but this can also vary. The bars are probably 1/2" in diameter. I would typically refer to plans of the house, if they are available, or you can rent small radar-based devices (roughly the size of a large dictionary) that can tell you where the rebar is located and its size without busting out any concrete. You want to leave at least 2", ideally 3" of solid concrete between any piece of rebar and the edge of the concrete.

In your case - since it's just one small hole, and if you elect to go through the foundation - I would just drill the hole with an educated guess: center your 2"-diameter hole 7" to 8" below the top of the foundation, and at least 18" from any vertical corner in the foundation wall. This will almost assuredly avoid any horizontal rebar, and will probably avoid vertical rebar. If you hit vertical rebar, you can move your hole 6" to the side and patch the first hole with concrete (kind of a pain but not a big deal and not expensive). Of course, if you have plans for the house which show the steel within the foundation, this would help you make a more educated guess. Note that plans are not always 100% accurate with respect to what was actually built. As-built plans are better than original construction plans in this respect.

Feel free to PM me with further questions if you like.
posted by hootenatty at 1:01 PM on June 1, 2015 [3 favorites]

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