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Deck Supports

Deck supports can be built many different ways. With pressure treated lumber, you can dig a hole and bury the post itself. Placed on a flat stone or small concrete base, the post should last as long as the deck. You can backfill with dirt, or if you like, back fill with concrete. However, my personal favorite is to pour the concrete in the hole, and mount the post on top of the concrete footer. I guess the concrete seems more permanent to me, and besides, it is cheaper to fill the hole with concrete than it is with a 6x6 of pressure treated lumber.

So in this article we will talk about building a solid foundation with concrete:

To Begin:

The main element that will determine the stability and longevity of your deck is an adequate foundation. To determine the foundation depth, you must consider your local frostline. Check the chart for regional generalities.

post hole

Suggested Support Depths

Albany, New York		42	
Albuquerque, New Mexico	18	
Anchorage, Alaska		42	
Atlanta, Georgia 		12	
Baltimore, Maryland		18	
Bangor, Maine		48	
Charleston, West Virginia	24	
Columbus, Ohio		32	
Denver, Colorado		36	
El Paso, Texas		6	
Greensboro, North Carolina 	12	
Knoxville, Tennessee	18	
Los Angeles, California 	12	
Minneapolis, Minnesota  	42	
Omaha, Nebraska 		42	
Portland, Oregon 		16	
Salt lake City, Utah		36	
Tampa, Florida 		6	

The bracket is an essential element in deck support. One of the commonly recommend brackets is a post anchor (TECO is a brand) that is U shaped with a support plate that fits under the post and over the bolt. Made of galvanized steel, it supports the base of the support post and allows some adjustment of the post on the concrete support for final placement. This adjustment is achieved through the use of a bolt inserted in the concrete plus a metal plate with a large hole and larger washer to secure the bracket to the concrete. The bracket size depends upon the size your support post. For instance, a 4X4-support post will use a 4X4 bracket.

post bracket


Placing The Supports

Support placement will be determined by the size and shape of your deck. Diagram the deck and check with our article on deck building to determine adequate stability and weight bearing using the tables referenced in the article. Once you've designated the support locations clear the area of debries and mark your support sites .

From there a few easy (to describe) steps will lead you to the beginning of a stable deck.

  1. Prepare a hole of suitable depth for each support; footings must extend under the frostline. This is usually 24 to 48 inches. take care to avoid underground power or telephone cable.Call the power company if you are unsure of any underground wiring. A power post hole digger can make short work of the digging. They can be rented from most equipment rental places for under a hundred dollars, and can make short work of the digging.
  2. Fill the hole with five to six inches of gravel.
  3. Mix the concrete mix as directed on the package.
  4. Fill the remainder of the hole with the concrete. I like to buy cardboard tubes called sonotubes to use for the top 6 inches of the hole. By cutting 6 inch sections of the tube and placing them at the top of the hole, the concrete can be poured to a level just above the grade, and a nice finished appearance is achieved.
  5. Place a foundation bolt (at least six inches long) in the concrete. Allow the concrete to harden. Having the bracket in hand, you will know how much of the bolt to leave above the concrete. (Usually about an 1 inch)
  6. Attach the bracket to the bolt, using a washer and a nut. Tighten securely only after the posts are placed on the brackets and the beams placed on the posts. This will allow you to move the posts this way or that a bit to align all your posts under your beams. Place the plate over the bolt.
  7. Place the post in the bracket and nail the bracket to the post securely. The brackets come with galvanized, thick nails for securing the post to the bracket.

Connecting the Supports.

Once you have completed the placement of the deck supports, you are ready to begin the construction of the deck itself. When bolted to the support beams, the supports will stabilize the deck.
You may want to consult your building materials supplier about alternate brackets. Be sure you have the brackets before you pour the concrete, so you are prepared to place them in the concrete.
Once, I had badly placed the hole (something about a big rock I think) and I needed to place the post near the edge of the concrete support. The concrete had dried by this time and the bolt placement was wrong. I had to drill a hole into the concrete and use an expanding bolt to secure the bracket to the post. The moral of that story is, even with some adjustment allowed, you may not have enough and improvisation has to enter in.

What You'll Need

  • Concrete Mix
  • Wheelbarrow
  • Flat shovel
  • Gravel
  • Brackets (one for each support)
  • 4x4 or 6x6 pressure treated lumber
  • measuring tape
  • level


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Quantity Requirements in Pounds

(in 80 pound bags)
Hole dia.		8"			10"			12"		
Depth		lbs	bags		lbs	bags		lbs	bags	
12"		45			74	1		110	1 
18"		67	1		112	1 		166	2 
24"		90	1 		149	2		221	3
30"		112	1 		186	2 		276	3 
36"		135	2		222	3		330	4 1/2	
48"		180	2 		296	4		440	6

If you have any questions or comments on this article, please email us, we would be happy to help.



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