When it comes to creating an ideal outdoor space for entertaining guests or relaxing with family, a ground-level deck is pretty hard to beat. Its flat, stable surface is ideal for furniture or a grill, and you can make it as large or small as your yard and budget allow.
Ground-level decks are safer and simpler to build than elevated decks. A railing is typically not required by code as long as the deck is no more than 30 in. from the ground (24 in. in Canada). You can forgo attaching a ground-level deck to the house and instead simply secure it to the ground with permanent footings. And because a ground-level deck is closer to the surrounding yard, it’s often easier to integrate adjoining gardens, walkways and landscape features into the design.
Of course, with these benefits come important construction considerations. Because ground-level decks are in direct contact with the soil and are exposed to insects and blowing and splashing debris, it’s vital that you make the correct design and material choices.
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Here’s what you need to know to build a ground-level deck that will add lasting beauty and practicality to your backyard.
To dig, or not to dig?
A ground-level deck requires stable footings, but you’ll have more options for them than you would with an elevated deck. If you’re building on firm, stable, undisturbed soil, footings can consist of cast-concrete pier blocks placed directly on the ground. Pier blocks weigh about 45 pounds and have molded channels that accept 2x joists and 4x4 posts. Although cast piers are typically code-approved for ground-level decks nationwide – even in cold-weather regions that experience frost heave – it’s always best to check with your local code authorities before you finalize your plans.
Of course, you can always dig traditional footing holes that extend below your local frost line and fill them with concrete, just as you would for an elevated deck (which is what we did for this project). Footing holes should be wider at the bottom than at the top, creating a bell-shape profile for greater stability.
If you choose to use poured-concrete footings, you have three options for securing the deck posts to the concrete. The first approach is to insert a metal J-bolt in the center of each footing and fasten a metal post base to it after the concrete cures. The second option is to insert post anchors that have corrugated fins directly into the wet concrete. The third method is to use a hammer drill outfitted with a masonry bit to bore a hole in the cured concrete and then insert an expansion bolt that secures the metal post base.
Framing a ground-level deck
Unlike a raised deck that sits well above the soil, a ground-level deck is subjected to much harsher environmental conditions, and the framing needs to be up to the challenge. Ground-level decks require pressure-treated lumber that’s rated for ground contact. Although 4x4s and larger dimensional pressure-treated lumber are commonly rated for ground contact, typical 2x pressure-treated material is not. Some lumber suppliers stock ground-contact-rated 2x material (check the plastic tag that’s stapled to the board); if yours doesn’t, you may need to place a special order.
Besides being able to withstand harsh conditions, the framework of a ground-level deck may need to incorporate additional reinforcement, depending on the type of decking you choose. Some decking materials may require you to space the joists no farther apart than 12 in. OC for the main deck surface and even closer together for stairs and other specific structures. For example, because I planned to use Trex Brasilia boards (a composite decking product made from a combination of wood and plastic fibers) for the main deck and the stairs that would connect to the existing deck above, I had to space the stair stringers no farther apart than 9 in.
Low-maintenance deck materials
Although you can choose traditional materials such as cedar or pressure-treated decking, redwood, cypress or even hardwood such as ipe or ironwood, I chose Trex Brasilia boards because they are low-maintenance. Engineered materials such as Trex have a variety of properties that make them well-suited for ground-level deck applications. First, they are extremely rot- and insect-resistant. Second, the boards’ color is created during the manufacturing process, so there’s never a need to apply stain. (Because Trex does contain actual wood fibers, the color will weather slightly during the first four months of exposure.) Third, the boards can be bent to create interesting curved decking patterns.
Another feature that we found appealing for this project was that the boards are milled to accept hidden fasteners. These 1/4-in. self-gapping clips are installed from above the deck’s framework rather than below — the perfect approach for a structure where you don’t have access to the space beneath the decking.
If you’d rather face-screw the decking to the framework than use hidden fasteners, you’ll need to allow for the correct amount of space between deck boards. The minimum required gap is 1/4 in. (unless it’s colder than 40 degrees when you’re building; if so, increase the gap between boards to 3/8 in.).
Another low-maintenance choice we made was to use cellular PVC trim boards – in this case, Trex Trim – for the stair risers. Cellular PVC has a uniform cell structure that allows you to cut it, rout in, fasten it and paint it just as if you were working with wood. But unlike wood, it has superior resistance to rot and insects, and if you decide not to paint it, it retains its brilliant-white appearance.
To create a finished, unified look, we decided to clad exposed pressure-treated framing members with Trex’s matching fascia boards. Manufactured to match both the grain and color of the deck boards, these fascia boards come in 12-in. widths and easily screw to the face of the perimeter framing members. When attaching fascia boards to the framing, use three screws every 12 in. Drive the top screw 1 in. from the top of the rim joist, a second screw in the middle of the rim joist and the third screw 1 in. from the bottom of the rim joist.
Although this ground-level deck was built to tie in with an existing elevated deck, you can build your deck almost anywhere: tucked in amongst the trees as a private hideaway, floating in the middle of your lawn as a prominent gathering spot or abutting your house or another existing structure. With proper planning, the right materials and a little sweat equity, you can build a ground-level deck that offers years of enjoyment with no maintenance headaches.
Bending Trex
One of the interesting aspects of working with Trex is that you can bend the boards to create curved decking patterns. The process involves first taping together multiple 16-in.-dia. concrete forms to create one long tube. Sections of rebar are inserted through the tubes to create “racks” onto which the Trex boards are placed. A forced-air propane heater (140,000-Btu minimum) is then positioned at one end of the tube so that it blows hot air through the tube and around the boards that are sitting on the rebar racks. As the boards get hot, they become pliable.
Once a board reaches a temperature between 185 and 200 degrees, it’s removed from the tube and slowly bent to fit into a jobsite-built jig that mimics the curve required for that specific installation. The jig holds the board at the required radius, and as the board cools, it will permanently harden into that shape. Special framing requirements are necessary when installing curved Trex boards, so it’s best to consult with the manufacturer if you plan to incorporate curves into your deck design.
Recommended Deck Spans and Spacing
Though you should always check with the manufacturer of the decking material you choose and your local code authority, in general you can use the chart below to determine the maximum allowable joist length, depending on your choice of joist material. Simply pick your joist size and planned spacing to find the maximum allowable length.
Joist spacing (OC)
Joist size 12” 16” 24”
2x6 11’7” 9’9” 7’11”
2x8 15’ 12’10” 10’6”
2x10 19’6” 16’5” 13’4”