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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.

This black cone shaped product above is the BigFoot Systems . Its designed to spread the weight load of a deck over wide area and hence the need for less 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 am building a deck on top of a 36" man made elevated area that used to be a paver patio. The entire area has 36" of crushed 53''s inside the retaining wall. My question is do I have to dig the 40" below the frost line making me a total of 76" below the elevated area. The elevated area has been the for yen years so everything is well settled. Work is being done in Indiana. If not how would you do the footers. Thanks, Ryan

posted by Ryan at 8/27/2015 1:11:27 AM

I am building a deck off of my house that will span a small ravine on one side and connect to my house on 2 adjacent sides. If the span from ravine embankment to house is 14'', what size beam do I need over the span? Thanks

posted by lfwreaths at 7/23/2015 8:40:36 PM

I am a diy''er and need to build a deck low to the ground. The space is at a small slope in the corner of my back yard that leads to my in ground pool. I need some guidance on using or not using footing or placing above ground footings. So far all I was able to do is fill the corner with gravel but have not leveled it to start the deck. I downloaded plans but not sure where yo start. Any help I can get would be great, any suggestions?

posted by Tsporter1 at 6/14/2015 9:55:30 AM

I am having a covered porch added to the front of my house. The contractor said I do not need footers. He is planning on using 4-5 inches of crushed stone and pouring 4 inches of concrete over the crushed stone. I live in Eastern PA. Do I need footers to prevent ground heave?

posted by glhalljr at 6/10/2015 9:06:41 AM

I am building a free standing deck 15 ft wide along house and 16 ft deep. How far from house should my first posts be and the plan calls for them every 7'' 4 3/4". The post will go on cement piers in tubes with a bracket on top? (1) is this enough posts? (2) Is this the best method for using posts? My deck will be apprx 24 inches high above ground using 2x8 for beams and joists, 4x4 for posts and 2x6 for decking. This is first deck i have attempted so suggestions are appreciated.

posted by jimkim at 5/28/2015 1:13:50 PM

how deep do you have to set the post for footer and how wide across? This is for a wood deck

posted by harleyx1 at 7/13/2015 4:36:03 PM

Just to be helpful... (") means inches and ('') means feet. Maybe it is just me, but I find it difficult to read some of these comments when they are mixed up. Good luck on your deck building!

posted by akenuts81 at 5/25/2015 12:54:31 PM

found out that this is the problem. Computer shows: '' as "

posted by akenuts81 at 5/25/2015 12:55:17 PM

I have a 10'' pad extending off the back of my house where I wan to put a deck. I understand that I will have to cut the concrete pad and dig down to place the footings. If the footing tubes are round, and I have to cut a square hole through the concrete, after the footings are in place, do I just fill/level the top of the hole with concrete so it appears somewhat seamless with the rest of the pad?

posted by MDC2957 at 5/16/2015 6:12:49 PM

I''m building a 16x14 deck. My question is. I''m not sure if I should use a drop beam on 6x6 post or rest the beam on top? I might want to convert this to a three season room at some point. I want the deck to cantilever out or should I just make a box frame style? Any help would be appreciated.

posted by Paulf40 at 5/3/2015 11:03:13 AM

Drop beams are fine, cantilevered is not. (Deck construction guide from says 3-season must not cantelever, also must increase footing size.) Download the construction guide from this site (based on 2006 IRC), also DCA6 from (DCA6-12 is based on 2012 IRC). IRC is complex & just tells you requirements - fine for builders while DCA6 tells you how to meet the requirements - better for DYI folks!

posted by marckerstin at 7/23/2015 12:53:03 PM

I have a small 16'' x10'' deck plan in the workings... The deck is only 11" above the ground and a suggestion told to me was to bring up the concrete piers right to the 2x8 frame itself in place of using 4x4 or 6x6 posts of 11" in turn connected to the box frame. It makes sense to have the concrete raised above the ground to touch the frame but am unsure if this would be against any code. -Joe

posted by joe-fournier at 4/29/2015 11:01:22 AM

I am building a 12 x 14 deck. It needs to be designed for a 40-pound per square foot live load, we are in utah so I know it needs to be 30 in in the ground. Can you tell me how many footings to put into the groud

posted by pam richards at 4/1/2015 2:21:55 PM

I have a deck 35x25 how many post do I need

posted by edpass at 4/13/2015 8:19:29 AM

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''m going to cover my patio. Can I go 15'' between posts. I was going to use sandwiched 2x10 for the header.

posted by Mike57 at 5/20/2015 5:04:36 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