Installing Deck Footings

By Robert Robillard on Decks And Porches

What’s Important when Installing Deck Footings

If you want your wooden deck posts to be dead center in the middle of the concrete footing, then you need to have the outline of the deck built and suspended in the air.  Installing deck footings is very simple to do.

Trick for Lining Up the Footings

My way of installing deck footings starts by attaching the ledger joist to the house. Attach the two end joists of the deck to the ledger joist. Temporarily support the other end of the joists with a piece of lumber making sure the joists are level.


Image: renovatedsm.com

Nail the outer rim joist to the ends of the two joists that extend from the house. The outline of the deck is now complete.

Level and square the frame.  Once the deck outline is square, drop a plumb bob from the corners to establish these points down at ground level.

Use these reference points to easily locate the proper footing locations and dig the hole with a fence post tool.


Photo: concord carpenter

Installing Deck Footings:

A “footing” helps support the deck by spreading out the loads created by each post over a wider area. The wider base also helps prevent frost heave from lifting the deck.

Footings for porches are important in supporting and maintaining the integrity of the structure above. If the footings settle or heave then the building or deck does the same.


Photo: concord carpenter

Depth Of Footings

For this reason is always important to install deck and porch footings below the frost line for your area as well as make sure that the installed footing is on soil that will support the footings load.


Photo: concord carpenter

The frost line depth is not consistent around the nation because there is such a dramatic difference in climate from state to state. The frost line in southern Florida is less than a foot, while in northern Minnesota it approaches 6 feet.

The average frost line is Massachusetts is between 30 and 35”. The best source of information regarding your frost line depth is your local building department.

My inspector wants to see installing deck footings 48” deep.


Photo: concord carpenter

Footing Diameter

The diameter of the holes for your footings especially large ones, create significant concentrated loads within the soil. If you calculate the weight of the entire deck, the furniture placed on it and the combined weight of a large group of people who might be standing on it, you will be shocked at the number. Even a small deck might weigh in at 10,000 or more pounds.

If your deck has two wood support posts and a ledger board that is bolted to the house, each of the two deck post holds up approximately 25 percent of the total weight. In this situation, the soil under each deck footing may be called upon to support 3,000 plus pounds.

Depending on the porch load, the diameter of the hole will probably range between 8 and 24 inches in diameter. Larger diameter holes spread the weight out over more soil area.

I used preformed footing tubes called “sono-tubes” they come in different in 4’ to 10’ lengths. The tubes are cardboard and are easily cut with a hand saw.

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About the author

Robert Robillard

Robert Robillard

Carpenter / Remodeler / Editor / Writer / Video Talent

Robert Robillard is a remodeler, general contractor, and principal of a carpentry and renovation business located in Concord, Massachusetts. He also writes the "Ask the Carpenter" advice column in the Boston Globe, and serves as the Editor of Tool Box Buzz and founding editor of A Concord Carpenter . Rob is in charge of our Tool and Product Review - Tool and Product Review - Video Channel, , where we post all of our tool reviews and video tutorials. Rob enjoys using his knowledge and experience to help and educate building professionals as well as DIYers on best practices in the remodeling industry. The Concord Carpenter's motto: "Well done is better than well said!" : Read more about Rob <a href="https://profiles.google.com/concordcarpenter"

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