How can I ensure my deck is built square?
Figure 1 Photo by GollyGforce
Dear Keith: I am building my first deck and have been told that it's important to ensure the deck is built square. What does it take to ensure my posts intersect at a 90 degree angle? Stacy C. Dexter
The same system for measuring a “true square” or 90 degrees has been used throughout history by builders and carpenters. The only difference now is there are calculator-type products that can be used to do the math for you, such as a trigonometry calculator. If you left your calculator at the office, there is a simple process to help you make certain that your measurements are accurate. By confirming your deck is built correctly, you will save a lot of time and wasted material.
The process used to ensure your corners are at a 90 degree angle is known as 3-4-5 or the Pythagorean Triple. You may have heard the geometric law behind the measurement, known as the Pythagorean Theorem a² + b² = c². No need to worry if you’re not good at math; this is an easy process.
After your posts are set in concrete and before the concrete dries, put a string around three of the posts to make a triangle (refer to figure 2). From post “C” toward post “B,” mark and measure 3 feet. Then mark 4 feet from post “C” toward post “A.” The distance between the marks toward post “B” and post “A” should be 5 feet. If not, adjust your posts as necessary. Once the measurement is precisely 5 feet, you are ready for the concrete to dry, finish the deck and prepare for your next barbecue.
Figure 2
Paul is a State of Michigan Licensed Builder. Paul serves as President and founding member of Nationally franchised HandyPro Handyman Service, servicing Washtenaw, Wayne and Oakland Counties. Listen to Paul every Saturday at 11:00am on “It’s Your Home, Let’s Talk About It” WAAM Talk 1600AM. Email questions or comments to kpaul@handypro.com
Comments
Keith A. Paul
Fri, Jun 18, 2010 : 10:40 a.m.
Not so? As I said many times, if there are ten people in a room and youll have eleven ways to complete the same building project. Not that they are wrong, just different processes. These articles give our readers building processes they can use in other applications, such as squaring a door frame or wall, etc. Another reference for the squaring a building projects by national expert home builder Tim Carter http://www.askthebuilder.com/010_2_How_to_Square_Something.shtml
Andrew
Thu, Jun 17, 2010 : 5:50 p.m.
Not so, Keith. 1. The simplest way to assure squareness is to make all sides be the same length. 2. The next step is to measure the two diagonals to be within ~1/2" of each other. You do it while the posts are still free to move in the empty post holes. 3. Then you make sure the posts are 100% vertical North and West 4. You re-check the diagonals and adjust. 5. Repeat steps 1 through 4 until all fit. Secure the diagonals with scrap wood or strings. 6. Now you can pour the DRY concrete mix into the post holes, having made sure the post base is under the frost line, a 42"for MI. 7. Add water and what had been dug out from the holes, tamp it down with a 2x2, and let it be for a day or two. 8. After that, all you do is going to be fun.