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Post 55B – Laying out a foundation.

The foundation is the base of a building and must be square and level.   If not the whole project will be a fight from that point on and every board will have to be a special cut.  In other words extra effort here will pay big dividends in the rest of the job.

In this post I will assume a conventional building as is built in this part of the country and we may talk about modifications to this in future posts.   The building will be a simple rectangle as shown in the first picture and the foundation wall will be concrete block over a poured concrete footer.   For now no basement is considered so the house will be flooring over dirt creating what is commonly called a crawl space under the flooring.  This space will contain the plumbing, the heating-AC ducts, and the wiring.

The first step in laying out the building is determining the direction of one wall.  Normally, this is laid out parallel to a road or a boundary or possibly an existing building.  Once this is determined, a corner post is driven into the ground for a temporary reference point.    Next, approximately 3 ft. (1 meter) outside the foundation three posts are driven for the batter boards as shown in the second picture.

At this time it two things must be done and thought about at the same time.  First, do a rough layout of the building by measuring to the second corner of the side of the building you will be aligning to the with the road or other object.   Then rough layout the other two corners.   The top of the foundation wall needs to be a whatever height you choose above the corner that has the highest land if the land is sloping.   The height of the horizontal boards on the batter board will have to be that height or higher. At this point you can attach the horizontal boards on the batter board at the “master corner”.  Make sure the horizontal boards are level and are the same height by placing the level across the two boards.

Now at the three remaining corners again drive the 3 posts approximately 3 ft from the corner. The height of the horizontal board at each of these locations is determined by pulling a line from the master corner to each of the adjacent corners and making sure the line is level.  Once the adjacent corners are level, these can be used to level the corner diagonal to the master corner.  Again at each corner make sure the horizontal boards are level and at the same height.

Set the two lines from the master corner so they are directly above the corner stake as shown in the 2nd picture.  Get these two lines square with each other by checking with a framing square and continue on to the other lines.

Once the four lines are initially set up check the measurements again where the lines cross and make sure these are the exact outside dimensions of the building.  Next, do diagonal checks from opposite corners to make sure all the lines are square with each other.  Then as a final check make sure the lines are level.   Lots of measurements here will pay off once the building is started to be constructed.

Drop a plum bob from these lines to determine where the foundation trench needs to be dug.   Note each part of the foundation footer will have to be below the frost line as discussed in the previous post.  However, if the land is sloping it is possible to step the footer in one or two concrete block increments (8″) so the footer will remain below the frost line yet the top of the foundation wall will remain level.

Before digging mark where each line is on the batter boards.   More than likely you will bump the lines during the digging process and will have to recheck the lines when putting in the forms for the footer and possibly again after the footers are poured and the walls are built.   The top of the footer forms will be determined by measuring from the lines pulled from the batter boards.

References for this post:
Episode 5 — Making Things Square
Episode 9 – Making things Level.
Episode 14 – Measuring Plumb


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