Deck Post Footings Size

The number of footings needed to support a deck beam is dictated by the beam s size.

Deck post footings size.

Diameter center footing size and table b3 calls for a 16 in. Depending on how heavy and high your deck is your concrete footing underground may take 1 4 bags of concrete. Step 2 dig footing holes about 6 inches deeper than required. In this case though i couldn t find a current source with a table that shows allowable tributary areas for various sizes and wood species of posts.

To calculate the load you should use 40lbs per square foot for live loads these are variable loads that are dynamic such as the weight of. Post spacing is going to depend on your design local building codes the size and length of your beams and the size of your posts. A good size for a common backyard deck is a 10 or 12 diameter for the sonotube and a 20 base diameter. Typical post size is a pressure treated 4 4.

Of course you can get a 24 base size and it will spread weight over an even greater surface area. In order to determine the proper size for your footings you will need to establish how much total weight they are going to have to support and what kind of soil they are covering. A comparison of the footing sizes i calculated for the example deck resting on 1500 psf soil in the sizing deck footings article and dca 6 table b3 shows an almost identical result. For aesthetic reasons most deck builders size them all based on the worst case loading.

The american wood council publishes the prescriptive residential wood deck construction guide which is based on the international residential code irc. Use added batter boards and string to mark rows of posts. My calculations came up with 15 3 4 in. Once you decide the distance measure from the house for the first row of boards.

Unless the deck requires engineering i refer to a beam span table as i design the framing. This is between 3 and 14 in concrete. Footings typically must extend below the frost line to prevent shifting during freeze thaw cycles. The size and spacing of footings tie directly to the maximum spacing between posts of the beam they support.

A larger beam can span a greater distance requiring fewer but larger footings. Deck footing size chart. Step 3 fill the bottom of the hole with 6 inches of gravel and compact the gravel with a 2x4 or wood post. This is a permanent footing and is great for large or high decks that need very strong footings.

There is little material cost to a buried post footing.