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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


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