Lifting the House A Chronicle of Mayhem and Plunder

Pouring the Floor Slab

First the plumbing

The old slab was demolished and the house was up in the air, sitting on cribbing piles. The new foundation walls had been formed and poured, and the forms were removed. It was time to pour the new floor slab, but first I had to install all of the new plumbing that would run under it. This included the sewer lines and the incoming water line. Most of this entry is going to be about the plumbing because it's the part I did. When it came to pouring the floor all I did was watch.

The existing main sewer line ran out the back wall just above the old foundation, under a kitchen addtion we built 12 years ago, where it ducked down into the dirt. Then it ran across the back and down the side of the house to the street. When the house was lifted, the lift crew cut the sewer line where it exited the house, and installed a temporary line that just went through the basement area and joined the section running beside the house. They actually framed a window opening around it.

Because we are installing a half bath and laundry room in the basement, the new sewer line had to run under the floor to join the pipes from these rooms. Under the slab is a 4-inch layer of gravel, then a layer of 2-inch solid pink insulation and a 6-mil plastic vapor barrier. The sewer pipes are partially in the gravel and partially in the dirt beneath it. I didn't want to dig a lot of trenches through the dirt so I waited until the gravel was spread. Then I put the pipes in the gravel.

I thought that would be easier, but in retrospect the bare earth probably would have been easier to deal with. In don't want to go into the intricacies of the sewer line here because building codes probably vary from place to place, but basically the size of each section of pipe depends on what is draining into it, and the pipes must slope downward a designated amount. All the various runs eventually join together in a 6-inch line that runs to the southwest corner of our house, ducks under the foundation and joins the original pipe outside.

My only advice is that digging under the foundation was a real bugger. Very awkward work. The foundation footing is 18 or 24 inches thick. That's a lot of distance to tunnel. If you do your own plumbing I highly recommend digging out a trench and running a few feet of 6-inch pipe under where the foundation will be, using the correct slope and everything, before the foundation is poured. To prevent stray dirt getting in the pipe you can put temporary caps on it without glue, or just stuff the ends with newspaper and cover them with Hefty bags. The lifters told me they could create round holes for pipes when they pour the foundation, but that structurally it's probably better to run them underneath. If you put pipes through concrete you have to put some kind of sealant around the pipe. Moisture can get in around it if something goes wrong. It just sounded to me like going under the foundation was smarter.

The incoming water line was a similar story. Wish I had dug it in beforehand. My mistake with the water line was that I thought city water came in as a 1-inch copper pipe. This was based on looking at the big thick steel pipe that we had lived with for so many years. I know what 3/4" steel pipe looks like, and our main was a lot thicker. But it turns out that in Seattle they run 3/4" pipe to your meter, so there's not much point running 1-inch from there to your house. I didn't find this out until after my short section of 1-inch pipe was installed, complete with expensive 1-inch main valve, and the floor was poured around it. So now I have 3/4" coming in from the meterto just outside the house and joining with a curious 1-inch section for the trip under the foundation which goes back to 3/4 after it comes up through the slab. Oh well, doesn't hurt anything. It's just a little strange, and the 1-inch fittings were harder to solder than 3/4.

One important consideration was the toilet flange. This is a special fitting that goes onto a 3" PVC pipe. The poured concrete has to come just up to the bottom surface of the flange, no higher.

Anyway, you can see in the pictures there's the gravel layer, then the rigid pink foam insulation and vapor barrier, then the crew placed re-bar on top of that and poured the slab. Not much else to say about it. Earlier they had poured some thick footings, including a really big one that the structural engineer specified for under the main bearing wall that runs through the middle of the basement. These got covered up by the slab, but they had some steel brackets embedded in them that stuck up through the slab, onto which the posts would be bolted later.


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