Mudsill Layout for a Complex Foundation

To anchor the string, we tacked two blocks to the front left corner of the house using a powder-actuated nailer. The block along the side wall was for attaching the string, and a perpendicular block on the front wall located the exact position of the string. (We always use the inside edge of the plate for our baseline.)

Because of the unusual jogs in the front of the house, the front of the garage was 3 feet in front of the end of the house where we'd attached our blocks, but 2 feet in back of the center section of the house. We measured back from the corner of the garage and marked the baseline location, which fell in the opening for a side door to the garage. Now we were able to stretch the baseline string over the entire length of the house.

Once we had this line established, it was easy to pull parallel measurements for each of the four walls along the front elevation. We then snapped chalk lines between each set of measurement marks.

My foreman hooked a tape on a 2x6 block aligned with the baseline string. Standing on the back wall, I held the other end of the tape, keeping it level. Another crew member positioned the laser on a block on the dropped wall and moved the block until the plumb line was at the exact measurement, then marked the spot on the dropped wall.

We repeated this process at the other end of the wall, which gave us two accurate points for snapping a second baseline along the dropped wall. We used this line to pull parallels for the other rear walls at that same foundation height.

After removing the temporary sill that held the baseline string, we measured the side wall and marked the position of the inside edge of the plate.

Then, making the assumption that the foundation contractor had gotten the dimensions correct, we did the same with the front wall of the garage and marked the opposite corner.

With the corners of the garage marked out, we pulled diagonal measurements to ensure the layout was perfectly square.

But with a mobile-phone app or a construction calculator, you can simply enter the exact measurement of both walls, and the program gives you the diagonal measurement. On this foundation, the diagonals were off by only 1/4 inch—a pretty small amount in the scheme of things. Nevertheless, we corrected by shifting the back corner slightly, then double-checked our diagonals until they were perfect.

Once the four corners of the garage were properly marked, we snapped chalk lines for the two side walls of the garage. We now had our perpendicular guidelines for the rest of the house.

As had been the case earlier, pulling parallel measurements along the front of the house—where the foundation height was consistent—was easy. To make the process go more quickly, we refastened the mudsill for the garage sidewall using the line we'd just snapped.

Then it was simply a matter of one crew member holding the tape on the mudsill, while a second person marked the measurement on the foundation at both ends of each wall.

We had already marked the front left corner (at the opposite end of the house from the garage), so we marked the same measurement at the back just before the foundation began to step down.

To locate the back corner of the house on the stepped foundation, we again used three sets of hands and a laser. One person held the end of the tape on the back corner of the garage, while a second crew member stretched the tape. Then a third crew member set the laser on a block and moved it until the plumb beam was at the exact measurement for the overall width of the house.

One way we sped up the final part of the layout was to attach the sill stock to the foundation of the walk-out wall before locating the key points on the wall. We let the stock run by the corner of the foundation so that we could mark the exact length of the wall directly on the sill.

We had used the original reference line along the walk-out wall to lay out the rear wall of the rectangle, so we just needed to lay out the two perpendicular walls. As with the garage, I used a mobile-phone app to get the diagonal measurement to locate the two outside corners.

We finished snapping the sill lines and installed the remaining sill plates with the sill seal already stapled to the sill stock as it went down. (At this stage, we temporarily fasten the sills to the foundation with a powder-actuated nailer. Later, after the floor framing is complete, we'll use special bolts to permanently attach the sills.)

We run continuous sill everywhere the framing will touch the concrete foundation, including on vertical walls where the foundation steps down.

We make sure those sills are plumb before they are anchored. When all the sill stock is attached to the foundation, we saw off any overhanging extra where we'd left the stock long.

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