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How To Build A Deck - Footings & Foundations

Footings are a very important component of deck construction because they provide the solid foundation that will support your deck. Your deck’s design will determine how live and dead loads are transferred from different sections of the deck to concentrated points of contact with the ground. The more footings your deck has to distribute the total load the less weight each footing will need to carry.

In effect your footings act to spread the heavy load of the deck from the surface of a support posts over a larger surface of soil so the ground can adequately support it. Without footings deck support posts could sink into the ground under the weight of the deck. Footings also have to be installed lower than the frost line to prevent the deck from moving when the soil freezes in the winter. A pier is often used as an upright support to connect the buried footing pad to the structural post above grade. The soil conditions and the climate will determine the size and depth of your footings.

The IRC requires frost footings to be installed for all decks that are attached to a house in most climate zones. These footings will have to be inspected to make sure they are capable of supporting your deck and will resist damage from frost. Because footings are installed under ground they will have to be composed of materials that won’t decay. Usually footings are made of concrete. There are many different methods for installing footings, each type offers its own set of advantages and disadvantages. Installing frost footings usually involves making a mess of your yard and often require some hard labor if you do it by hand.


Comments, Questions and Reviews


i have a 20 x 20 concrete patio on the back of my house and i was wanting to build a deck in the same rough footprint. do i need to remove the whole thing a pour footings or is the a way to leave it and deck over it. it is 16" below where i want the new deck to sit

posted by lococok at 3/24/2015 6:44:58 PM

I am building a deck around a 24'' pool 6'' around with a 10x10 sitting area my plan was to use 4x4 on top of footings with a 2x10 beam and 2x8 for joist it will be all trex except framing of course with the post being no more than 7'' apart with beams directly on top of post and I do not want any movement in my deck should I bury the post or set on top

posted by joeh at 3/20/2015 3:51:49 PM

I would recommend using 6x6 posts. You can use either a buried post or post base on top of a concrete pier.

posted by mike at 3/23/2015 9:09:09 AM

Thanks Mike I will use 6x6 now would you cut notches in all those post or would set the 2 2x10 beam on top of the 6x6 post

posted by joeh at 3/23/2015 3:41:50 PM

I would set the 2-2x10 on top of the 6x6 and use a post base connector.

posted by mike at 3/24/2015 8:54:48 AM

I am building an attached porch that will be 20''x33''. How deep and wide should my footers be? It is a sandy area.

posted by achave at 3/9/2015 3:42:44 PM

I am planning on building a deck this year,my current patio is 12ft by 24ft. I would like to go a little bigger in size. I live in a tri level so attaching to house won''t work. After installing a new fence last year I was wondering if I could do the same by digging below frost line,add the post and then sack create and go from there? Or do I have to dig down then add a footer and place posts on top footer? Thanks in advance.

posted by Sandman at 2/27/2015 8:44:48 PM

You will need to have a footing at least 12 inches thick below the post.

posted by mike at 3/2/2015 9:04:56 AM

I''ve always been confused with the various methods. I''ve seen it done where the post is in the ground and dirt is back-filled, but most of the videos I''ve watch have the post above ground attached to a bracket. I am buiding a tree house and I feel safer with the post in the ground. What is the recommened approach?

posted by deckdrunk at 2/26/2015 12:48:17 PM

I would recommend installing the post in the ground. Make sure you are using ground rated pressure treated wood for the support posts and that they bear on top of the footings.

posted by mike at 2/26/2015 4:18:21 PM

Can I use 4x4 posts on concrete piers to build an 8 foot by 40 foot deck. The low point of the deck will be 2 feet off the ground and the high point will be 4 feet off the ground. The piers and 4x4 posts will be 6 feet apart. The side connecting beams will be 2" by 10" and the 16"on center cross beams will be 2" by 8". The soil for the concrete pier blocks is cherty in nature and very firm. The decking will be a composite material.(TREX) The railing will be RDI. John

posted by John Boyle at 8/28/2014 12:23:56 PM

I would recommend using 6x6 support posts with a minimum of 12" diameter footings with a 2-2x10 beam.

posted by mike at 8/29/2014 9:03:38 AM