How To – Constructing Footings For Decks

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    Constructing footings for your deck or porch project is relatively easy if you take time check the span charts for your beam and measure the locations correctly.

    Some contractors will install beam posts directly in the ground with a small footing at its base and surround it with concrete. This is probably not the best way to build a deck because the concrete surrounding the wood post will eventually rot the lumber. Even pressure treated lumber will rot and embedding it in concrete that will hold moisture speeds its breakdown.

    For a long lasting solution the best method is to build a footing from concrete and attach the post to the footing with a post support.

    There are 2 standard ways to build footings.

    The first and fastest way is to use Sono Tubes which are available at most supply centers. You may have noticed them in the concrete masonry section.

    A post hole digger is used to dig a round hole 8 to 12 inches wide and about 4 feet deep. The sono tube is placed in the hole and acts as a form for the concrete to be poured into. This method is pretty simple and it will be up to your building official if they let you use this method.

    In our project we will be building basically a 2x2x2 foot cube of concrete as our footing. Although it does not go down below the frost line the size of the footing is large enough that no heaving will occure. This is the method that our building official required after they rejected our request to use sono tubes.

    To build our footings we first need to layout the location of the center of the footings.

    Using a string line we measure out from the ledger board that will support the inside ends of our joists finding the center of the footings. A temporary 2×2 stake is driven in the ground to set the string line.

    Once we have established the center line of where the beam and footings need to be we can measure out from the other side how far apart the footings need to be.

    Now we can build our 2×4 form caps that will rest on the surface of the dirt and provide a way to level our footing.

    Make sure the opening of the form is the finished size you need.

    Place the form on the ground and mark the inside of the hole to be dug.

    Now dig all of your holes (easier said then done)

    When digging the footings it is easy to have a smaller base or walls that angle in. You should use a plum bob and tape measure to make sure that the whole is as deep and wide as you need it to be.

    Once the hole is completed you can install the form caps. Check their level and square to the building and make sure they are all lined up correctly with the center-line of where our beam will be placed.

    In our situation we have one footing that is close to our homes foundation. Because it is important to protect the homes foundation we insert foam insulation board between the wall of the home and the wall of the footing. In some cases when pouring a footing for an addition you may want to connect the new footing with the old foundation and to do so you would insert rebar in the old foundation to tie the pieces together but when supporting a small deck or porch it is more important to protect the homes foundation from any possible settling or heaving of the porch footing.

    So now that the forms are set and we have approval from the building official we can start filling the holes with concrete.

    You should work on one hole at a time. Concrete is pretty forgiving but you want to finish each hole before you move on to the next one. You should also complete each footing and not try to come back the next day.

    When the footing is filled to the top of the form you can use a trawl to finish the surface and angle it very slightly towards the outside edges. An Edger tool will clean up the edges for a nice look.

    Our posts will be connected to the concrete footing with a L shaped anchor and steel post adaptor.

    To make sure the bolt threads don’t get filled with concrete and that it stays perpendicular to the footing we use scrap pieces of luan plywood. Place the nut on the threads and insert the luan square. Insert the bolt into the footing and give it a 1/4 turn so the L part sets in the concrete and it gets a good grip inside the concrete.

    After the footings have set up for about 2 hrs you can remove the nut and remove the luan and clean up the concrete.

    After a night or at least 7 hrs of cure time you can attach the post bases to the footings.

    Because the concrete is still not cured completely you do not want to tighten the nuts extremely tight. It will take about 7 days for the concrete to fully cure so you should return to the post bases later and re-tighten them once you have completed installing the deck if needed.

    To get access to the bolt you leave the front plate of the post base bent down then you can reach in with a standard wrench to get to the bolt later after you have attached the post. 

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