Survey Says…

Plenty of progress to report. Colin and I reassembled the Barn stairs, mostly without supervision from Terry, although he did save us from gluing the landing upside down. I fitted some 1-inch PVC pipes together to make an electrical conduit that will run just underground across the front of the Barn. Terry and I removed roof jacks; it’s amazing that just hammering down a few nails under the shingles hides all evidence the work platform ever existed. Most importantly, the House excavation is complete, allowing us to perform the all-important task of surveying the foundation.


Surveying 101: sighting elevation with a transit.

I never took a surveying class, so I’m learning everything on the fly. Key equipment are a transit (basically a telescope that sits exactly level and spins 360 degrees), a tripod to hold the transit steady at a comfortable level, an extendable measuring stick, and plenty of other measuring tools. We worked out the plan layout first, using a pair of measuring tapes and some basic geometry to triangulate each of the foundation’s eight corners. The Pythagorean theorem is critical for checking right-triangle diagonals, and I even invoked the Law of Cosines a couple of times because the House sits at a 15-degree angle to the Barn. (Our first mockup layout attempt wound up more like 30 degrees and placed us well off the excavation. Quote-of-the-Day from Todd when we finally got the angle right: “My hole’s looking better!”) Then we continually rechecked dimensions as we screwed together formwork for the 20-inch wide perimeter footer.


Terry, Colin, and Cole check the excavation with a mockup.


Triangulating the southwest corner. (Todd and his assistant from Pillsbury Excavation look on.)

We next used the transit and the measuring stick to sight formwork elevations around the perimeter. We chose 3.58 feet as our goal: the measuring-stick elevation we wanted to sight through the transit everywhere. Most locations were within a couple inches from the start, and we coaxed each point until we reached 3.58 feet, either shoveling gravel under the form to raise it or whacking the form with Sluggo to lower it. Then we staked the formwork to hold it in place. We also shoveled gravel against the forms to prevent wet concrete from leaking out, and we screwed spacers at regular intervals to prevent the concrete from spreading the forms more than 20 inches apart. We hung zip-ties from the spacers to hold our reinforcing steel bars at the height we wanted.


Rebar placement, slightly more sophisticated than last time.

OK, so the footer forms are level, but what about their elevation relative to the existing Barn? That’s just as important, right? Well, we also used the transit to determine the elevation change between the Barn slab and the House foundation: 7.08 feet. To match the plans exactly, we would’ve liked the foundation a little lower, but Todd hit ledge during his excavation and dug as deep as he could go. (Incidentally, there are major benefits to hitting ledge; one is that you don’t need to build a frost wall because bedrock doesn’t frost-heave.) It took numerous iterations to determine the exact configuration of finish floors, ICU wall heights, and number of stairs that would make our elevations work, but we eventually resolved all our math and agreed on a configuration. Early versions of the final drawing below can be found on lumber scraps, on a wall stud in the Barn, on the back of Colin’s copy of the plans, and in each of our heads… ah, how I love this job!


Designed by everybody. Checked by everybody. QC by everybody.

One thought on “Survey Says…

  1. Pingback: Two Hundred Fifty | PERCH ENGINEERING PLC

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