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Guide to building low and ground-level decks. This article describes the construction of low and ground-level decks, including questions of deck support, how beams are used, and how to construct overlapping joist connections over beams on large decks. We explain the construction features of floating decks and we include warnings about short or shallow deck posts. This deck design-build article series describes construction details for decks and porches . Our page top photo shows a ground-level deck inspected in Poughkeepsie, NY.
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Low decks are sometimes a choice and other times a necessity. If the floor of your house is close to the ground, if you need to keep a deck low to avoid an overhead obstacle, or if you just want to create a dry, flat, freestanding surface away from the house, the techniques on these two pages should offer a solution.
A ground-level deck can also serve as the lowest part of a multilevel deck.
Bear in mind that you can usually lower the height of a deck by using smaller joists and beams, a change that requires you to reduce the beam span (by pouring more footings and piers) and reduce the joist spacing (by using more joists).
Another strategy is to install joists on the same level as the beam, as shown below, by using joist hangers to attach the joists to the side, not the top, of the beam.
Beam-To-Pier Framing for Ground Level Decks
One of the simplest ways to create a strong, secure deck at ground level is to build a normal deck, but without posts. The beams can be attached directly to the concrete piers using post bases sized for the beams.
For a low deck that is not attached to the house, plan to install two rows of piers (more for a larger deck) with identical beams installed along each row.
Make the beams with double 2x members, with the inside board offset on each end by 1 l/2 inches to create room and a nailing surface for the end joist. Attach joists with joist hangers on the inside faces of each beam.
You could easily make a plan for a freestanding deck with very short beam and joist spans, requiring an intermediary beam, and 12-inch on-center joist spacing. This type of deck frame could be built with 2 X 6s, keeping it very close to the ground.
Beam-to-pier framing can also be used for decks attached to the house. Adjust the size of the beam or the height of the piers to align the frame with the ledger on the house.
Overlapping Joists on Large Low Decks
Larger decks typically require more than one beam, and this, in turn, generally means you will need to use two joists to span the distance from the ledger to the rim joist.
The best way to handle this transition is to have the joists overlap each other at the middle beam, as shown at left.
Allow at least 12 inches of overlap, and secure the joists to each other with 16d nails.
Note that this approach will result in the ledger and rim joist having different layouts. Rather than mirroring each other, the joists at the rim will be offset by 1 ½ inches from the joists at the ledger.
Joist Blocking on Low Decks May Still Be Required
Some building codes require the use of blocking (also called bracing) between the joists. Blocking can strengthen floors that have deep joists with spans of 10 feet or more. Check your building code for specific requirements. Blocking should be cut from joist stock. Snap a chalk line across the tops of joists, then install blocking on alternating sides of the line. Toenail the blocking with three 12d nails at each connection.
Should you Build A Floating Deck with No Footings?
A small platform deck requires no footings. The foundation will be provided by two 4x6 timbers, which are partially buried in the ground. You may want to remove any sod from beneath the deck.
Dig parallel trenches about 6 inches deep for the timbers, then add about 4 inches of sand to each trench. Set the timbers on the sand. Then level the timbers by adding or removing sand. The timbers should be squared up, with both ends equally distant from each other. Mark a joist layout on each timber. Install the joists with two 12d toenails driven through each side into the beam. Trim the joist ends, if necessary, and attach the rim joists. Install 2x6 decking with 3-inch decking screws, spacing the boards with a 16d nail for drainage.
Avoid Short Deck Posts
Decks built close to the ground often require very short posts. But posts under 10 inches in length, with nails securing fasteners at the top and bottom, are prone to splitting. You can usually design your way around short posts by increasing the beam size or raising the height of the concrete piers.
Either technique requires that the piers be level with each other, so make sure the tops of cardboard tubes are level before pouring any concrete.
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