Deciding to DIY the Foundation

Fri, Apr 19, 2019

I think we’re going to build the foundation ourselves. Actually, I have little doubt that we will.

Last year, we decided we shouldn’t build the foundation ourselves, but a lot has changed. The biggest part here is that the foundation is now much more complicated. That may sound like we shouldn’t do it ourselves, but hear me out.

The reason the foundation is much more complicated is because half of it will sit about 10’ lower than the rest. The northern half of our basement foundation will stair step down so that it remains on solid rock, rather than being on whatever fill exists there now (the southern half is uphill, on solid rock). Squaring our footings over this uneven terrain will be much more difficult.

I’ve been thinking about how we could ensure our footing is square. The traditional approach appears to be to set batter boards on the uphill side, and then build really tall batter boards on the downhill side, so that the tops are level with the uphill. Then you use the pythagorean theorem to check all the corners and adjust as needed.

For us, that’d mean building batter boards that are about 12’ in the air. Tedious, but not too difficult… although, how do we anchor them? These will be placed on solid rock, so it’s not like we can just drive some stakes into the ground to keep them in place. From what I’ve read, crews will indeed drill out holes in the rock to place their stakes. Pretty labor intense!

I recently discovered corner lasers. These are lasers that can shoot a perfect 90 degree corner over long distances, and over uneven ground. The laser is placed atop one corner, and will shoot a laser beam to the two adjacent corners. You use a plumb level and laser detector to detect the beam at the other end and mark that corner. Repeat around the perimeter of your site, and you’ve got all your corners squared.

We purchased one that has ⅛” error over 60’, which is within an acceptable range for footing and form work.

Another reason the foundation will be more difficult is because the rebar schedule is fairly intense. We are placing rebar up to every 8” on both horizontal and vertical runs, depending on how much earth the wall is retaining. We also have diagonal cross members at every opening.

A final reason for tackling the foundation ourselves is the bids we’re getting are much higher than we expected. Our first bid came back at $300,000. We had budgeted about $80,000 for the foundation, so obviously this was an issue. Our estimate was based on rough quotes we had received last year, before all the specifications of the foundation were finalized. We’re still waiting for a few other bids, but it looks like we severely underestimated the bid, and increasing the budget by that much is a non-starter.

This situation reminds me a lot of the challenges we faced when we decided to architect the house ourselves. The first time we looked at it, it seemed unsurmountable, but over time we start to see how the problems can be broken down into manageable chunks and at some point, the whole thing no longer seems so impossible.

I’ve been studying the plans all winter. I think our main challenge will be getting the footings square over an uneven and rocky terrain. Hopefully our new laser will help with this, but if it does not, we will know before any concrete is poured, and we can re-adjust as our plans as needed.

The second challenge we will have is the rebar schedule with ICF. ICF wants rebar on horizontal runs every 16” (ours is at most, 15”) and on some interval of 6” on the vertical (ours are at 8”, 12”, and 15”). What this means is we won’t be able to use any of the pre-fabricated rebar channels that ship with the ICF. We will have to hand tie our rebar inside the forms somehow. Not impossible, but could become tedious.

We’re headed up this weekend to (hopefully) complete the excavation and begin laying out our footing forms. I’ve been playing with the new laser we bought, but I am really curious to get it on site and see how it does over a much larger area. If all goes well, we should be able to build a lot of confidence in this plan and get a better feeling for the level of effort involved.

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