Method to Square a Barn

The 3, 4, 5 Trick

• An old carpenter's trick --- 3,4,5 --- borrows from basic geometry. If you're trying to square the corner of a new barn foundation, you want it to be 90 degrees. Start at the corner, measure 3 feet along one exterior wall plate and make a mark. Make a mark at 4 feet along the other exterior wall plate. Measure from the 3-foot mark to the 4-foot mark. You'll be connecting the two sides with the third side of a triangle. If you measure 5 feet, it's square. If it's not, adjust the angles of the exterior walls until you get 5 feet. It's the ratios that are important, so for larger structures, you can use 6, 8, 19 or 12, 16, 38 and so forth.

Cross Measuring

• Another carpenter's trick, from Harvey Miller's "The Carpenter's Guide," recognizes that squares and rectangles have a few common traits. One is that they have 90-degree corners. Another is that they have the same perpendicular measurement from corner to corner. So if you measure corner to corner, crosswise, then the other way, you'll have the same measurement --- if your square is really square. If not, you've got a parallelogram and need to make an adjustment. It can be helpful to check squareness using more than one method.

Line Level

• If you want perfect 90-degree angles, start with a level foundation. In other structures, you probably would check the level with a transit level. Barns give you a little more margin of error, and if you're on a smaller budget, you can use string, which is cheaper than a transit level. Use fluorescent orange carpenter's string for visibility. Pull it tight so it doesn't have any sag. Then clip an inexpensive, plastic line-level to the string to turn it into one, long level. You can leave the string in place as you jack up or install a barn floor, bringing it into level with bottle jacks.

Squaring with Sheathing

• When old barns start to lean, they look like a parallelogram from the side, instead of a square. There are clever ways to fix this, but use care because you're dealing with a dangerous and unstable structure. Brace one side of the building and use a come-a-long or winch, fastened to a tree. If you don't have a good angle to anchor to a tree, you can use a metal cable and block pulley to achieve a straight pull from a tree situated off to the side. Winch the structure upright. Brace it temporarily. This process, if you fasten plywood sheathing to the exterior wall studs, will make the structure rigid again --- and square. Once it's plumb and the plywood is thoroughly fastened, you can remove the bracing and it will stand upright.