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megbikes 10-01-2013 04:22 PM

Water under slab in daylight basement
Hello forum! This is my first post, although I've been reading many posts here with great interest. I'm impressed by the knowledge and experience you all seem to have.

My husband and I are gutting our 1931 farmhouse in South Seattle, starting in the basement, of course. We have uncovered lots of fun structural surprises so far, but this weekend, while demolishing some of our basement slab to get to the plumbing main, we found the best one yet- some groundwater under the slab. Attached is a picture of the hole we've dug (it's pretty dry in the photo, but after 4 days of torrential downpour here, it is now filled with standing water). You'll also notice the funhouse plumbing job- what a marvel! We'll address that mess down the road, after we figure out our plan of attack on the basement.

In places where the slab is still in tact, there is about a 1/2" gap between the existing slab and the wall, which has us thinking that this water issue has made our foundation and exterior wall move a bit. The existing foundation clearly needs some reinforcement anyhow, so we're thinking about pouring a strip footing next to the current foundation wall to reinforce it and shore it up (and we would drill re-bar into the current foundation to join new with old). Technically this would probably be two footings- one on either side of the plumbing main.

My question- for those of you more experienced with foundation repair/ reinforcement, is this a valid approach? Ideally we'd probably replace the entire foundation wall, but I don't think our budget will support that approach.

We also plan to address the water issue through the installation of a drain or a sump pump. I don't think it is always a wet area, but it definitely sees a lot of water pass through in big storm events, and there was some evidence of cracking slab behind the drywall, once we ripped into it.

(PS- we already have permitted structural drawings for this project, and the next step is a phone call to the structural engineer, but I thought I'd check with the brain trust here first). Thanks in advance for your insights/ opinions!

Here are photos of the hole/ wall:

Here's a shot of the same wall from the exterior, so you can see the slope of the lot (the plumbing ties into the basement wall just under that boat leaning up against the house).

nealtw 10-01-2013 06:37 PM

It dosn't appear like you have much of a foundation. If you are ripping up the floor I would like to see a photo of other areas of the foundation, mostly the front of the house.

megbikes 10-01-2013 07:01 PM

You are definitely correct that there is not much of a foundation along that wall with the plumbing (the north wall). The front of the house (east wall) has a more substantial foundation, which also includes a strange CMU wall. I don't think the house originally had much of a basement or foundation, but someone dug out a basement at some point. The structural plans call for some additional footing reinforcements along the east/ front and the south (not visible), which we've basically finished, as well as shear walls all the way around the basement exterior which bolt to the slab. It is a super funky, heady scratcher of a place (but it was cheap!). Here are pics of the foundation of the front of the house:

(this was earlier in the demo process)

Southern half of the eastern wall:

Northern half of the eastern wall (sorry for the lousy photo):

nealtw 10-01-2013 07:39 PM

I am glad to read you will involve an engineer in this. The foundation you would expect to see is a conrete wall that is sitting on a footing somewhat wider than the foundation. The total depth of the concrete footing would be below frost line which I think is 18" below ground level in Seattle and then 8" above ground level. In a house like yours, you would expect the top of the footing in the front to be just below the floor and where the plumbing is it would be about 12" below ground level.
Just a guess but it looks like at one time the front wall of the house was leaning in and someone added more wall just to hold it back.
Are you on city sewer or septic system.

megbikes 10-01-2013 10:58 PM

Thanks Nealtw. We are on city sewer. My husband cut out a strip section further along the wall today, more photos attached. It does have some more depth to the foundation further along the wall, away from the plumbing, probably 16 - 18" below ground level. Is this enough to tie a strip footing into?

megbikes 10-01-2013 11:05 PM

To clarify, the brown strip is concrete, but the width is no wider than the CMU block sitting on top of it.

nealtw 10-01-2013 11:28 PM

These are questions for an engieering company, a geo-tech should check the soil condition and let you know what needs to be done to make the system strong and do the required job.
More likely they would require underpinning which would be digging under that wall about 8" and putting concrete under it to support the wall. That would be a new footing wider than the wall, you would do that just a few feet at a time. But again I would not do it with out the engineer or geo-tech being involved.

BridgeMan 10-02-2013 12:09 AM

Why not consider digging a bit deeper, and then embedding a drain-tile system leading to a sump pit, before you pour that strip footing? Doing so would address some/all of the water problems you're experiencing.

P.S. Hubby deserves an "attaboy," as it looks like he's doing a decent job. And his bib overalls show his heart is in the right place, too (meaning he's a worker, not just a dabbler).

megbikes 10-02-2013 11:46 AM

Good point Nealtw. I'll ask our structural engineer if he thinks we need to under pin the wall.

BridgeMan, thanks for the suggestion on the drain-tile / sump pit- we're working on a drainage solution, I'll pass your suggestion on to hubby. And you are right, he definitely deserves an "attaboy!" He's getting it done!

Thanks to you both, we appreciate the help!

nealtw 10-02-2013 12:37 PM

Best is to water proof and drain from the outside but as you have the inside open already, you do want to catch any water coming thru the wall and have drain holes in the bottom of the block so they don't fill up with water.

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