DEAR TIM: I often hear my builder talk about the importance of things being square. When is something square and is there a simple way that I can tell if something is square? R. J.

DEAR R. J.: Something is considered square when two intersecting lines on the same surface create a 90 degree angle. It is vitally important for all aspects of your project to be square, especially the foundation. Square foundations allow a builder or remodeler to work at the highest level of productivity. All aspects of rough carpentry become a breeze instead of a hassle.

It is easier to install materials and fixtures when framing members and walls are square. There are fewer irregular cuts in most instances. Possibilities for mistakes are minimized.

There is a very simple way to check if something is square. This method has been in use for thousands of years. Starting at the intersection point of the two lines, measure down one line 3 feet and make a mark. Measure down the other line 4 feet and make a mark. Measure accurately in a straight line between your two marks. The distance between the two marks will be exactly 5 feet if the two lines are square. This third line makes a triangle. It is often referred to as the diagonal.

Any multiple of these numbers works as well. For example, a triangle with legs of 6 feet and 8 feet with a diagonal of 10 feet will produce a square corner. The combination of 12 feet, 16 feet, and 20 feet will also produce a 90 degree angle.

You can purchase handy calculators that will give you the diagonal for any combination of two lines. For example, let's say you want to build a deck that will be 20 long and project 12 feet out from the house. Using the fancy calculator, it would tell you in a matter of seconds that the diagonal would be 23 feet and 3 and 7/8 inches.