A square corner is one of the most important facets of quality construction, in particular, framing. If you do not have a square corner, you will not have a square room, causing the walls to be different lengths, cabinets won't fit, etc. Obviously a framing square is one of the best ways to ensure a square corner, but this is not always practical or available.
So, without a specific tool, how can you ensure a square corner? All you need is a tape measure and geometry will do the rest. The method we are going to use is called the 3-4-5 rule. Geometrically, if you have a triangle (which by definition means you have a 90 degree ,or square, corner) that has one side at 3 units (such as feet) and another side at 4 units, then the diagonal will be 5 units. If these measurements exist, then you are sure to have a square corner.
To use the 3-4-5 rule, simply measure out two sides of a triangle, one side for each wall, on the inside of the corner. This is easiest to do before you build the wall or set the plate. Often it is best to do this with chalk lines or a single piece of wood until you have found square. Measure one side (wall) to 3 feet and make a mark. Measure the other side (wall) to 4 feet. If your wall is square then the diagonal between the two marks will be exactly 5 feet. If the diagonal measures more than 5 feet, your corner is over 90 degrees and you must move one of the walls towards you. If you are under 5 feet your are less than 90 degrees and you must move one of the walls away from you. It is that simple. Just keep adjusting the marks until meet the 3-4-5 rule.
Autor: Dave Gray Dave Gray
Level: Basic PLUS
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Added: September 22, 2009