You’re probably thinking of how you’ll enjoy life on top of your new decking, but you first need to think about what goes underneath — the right concrete deck blocks and footings that keep your deck level, stable, and able to hold up any outdoor party you throw.
If you’re building your own deck, your first step should be to consult your local building codes for regulations about deck foundations. That way, you’ll know you’re building a deck that’s as safe as it can be.
In most regions of the country, that deck foundations must extend below the local frost line. Often, that depth is 36 to 48 inches below grade and can be as deep as 70 inches in the far north central section of the country.
In addition, deck foundations must be connected to the structure to prevent lateral movement caused by high winds, earthquakes, and frost heave. In most regions of the country, that means securing support posts to the foundation with code-approved metal connectors, or having the ends of posts set on concrete deck blocks buried at least 12 inches below grade (the top of the soil).
Here are your options:
Precast concrete deck blocks are popular for building decks. Some are made with notches designed to hold standard-size posts, beams and joists.
Precast blocks that are available at home improvement centers usually are 12 inches square and 8 to 12 inches high. Simply placing them on the ground or on a poured concrete pad a few inches deep usually isn’t enough to comply with codes — they must be set at least 12 inches deep in undisturbed soil. However, concrete deck blocks can be used without restriction for a freestanding deck that’s not attached to your house.
Some blocks have a hole in the center. This allows the insertion of a concrete bolt designed to secure a metal post anchor to the block.
Notched, precast concrete blocks help stop lateral, side-to-side movement but aren’t necessarily code-approved in all areas of the country — check with your local building authorities before you plan your deck. Some areas of the country may require the use of auger tie-downs — metal rods that are screwed into the ground and attach to deck framing members to prevent posts from lifting out of the precast notches.
Precast piers are long, tapered foundation supports designed to extend below the frost line, so they can be several feet long. They’re convenient to use because you don’t have to pour a footing (but you still have to dig the footing holes). And you may need special equipment to lift precast piers — they weigh up to 1,000 pounds each.
A good method for the DIYer is to dig footing holes that are deep enough and wide enough to comply with your local codes. Set cardboard footing tubes into the holes, backfill with dirt, and then fill the tubes with concrete. Set an anchor bolt into the wet concrete that you’ll use to secure a metal post anchor. Galvanized post anchors prevent lateral movement and keep the ends of wood support posts from direct contact with the concrete, which gives a post longer life.
Building a Deck
In this series, Chip Wade shows you how to build a deck from the ground up.