All Decked Out For Summer
(Page 4 of 10)
June/July 1992
by John Vivian
Test-dig a pier hole. If your soil is hardpan or rocky, you may have to hire a tractor with a post-hole auger or backhoe to get the foundation in. But in snow country, do not be tempted to install footings too shallow the deck will be heaved out of the ground by alternating freezes and thaws. Check your code, but in stable soils, footings2' deep should suffice below the Mason-Dixon Line; 3' through middle of the continent and 4' in far northern U.S.A., and Canada.
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It's easiest to attach ground-floor-level decks to wood frame houses with a ledger board. This is a 2" thick beam lagscrewed or through-bolted to the bottom members of the house frame: the massive sill of timber-frame houses or to the sill, joists, studs, and plate of stick-built houses. If your home is of stone or the ledger must attach to a concrete foundation, it can be affixed with masonry bolts set into expansion anchors placed in holes bored out with a drill and masonry bit. The easiest approach is often to forget the ledger and support the whole deck on concrete-and-post piers. (A freestanding deck built in modular sections with removable fasteners may be code-exempt to boot.)
The ledger joins with side and front beams supported on piers located at the deck's corners and at 8' to 12' intervals to form a square or rectangular frame. Beams can be square timbers or single or doubled 2" thick planks placed on edge. Joists running between beams support the planking.
Side beams plus joists can also be supported by the ledger and a dual-member carrying beam (or beams) set on 8'-spaced piers. Such a frame can "cantilever"—extend without support—beyond the carrying beam up to 1/5th of the joist's length (2' of a 10' deep deck). The cut ends of beams and joists are boxed with a rim joist.
So long as your deck rises no more than 5' above the ground and you use PT lumber, you should satisfy the code at least cost using 4x4 posts, 2x8 frame/joist members and 5/4x4 planking—which comes with square or—better—rounded or "eased" edges. This is all "nominal measure" lumber. For reasons lost in the sawdust of time, most dimension softwood lumber is sold as if a smoothing 1/8" or more has not been milled off flat surfaces and varying amounts off the nominal width. So, a 4x4 post is actually 3 1/2" square and a 5/4 x 4 decking plank is actually 1" thick and about 3 3/4" wide. Confusing. So, visit your lumberyard and measure the wood you will be using. Then draw up a scale plan using "actual" measure. Design in 1' increments, making any minor adjustments along the long dimension of your planks in 4" increments (the width of a deck plank).
A small entry deck close to the ground and less than 6' both ways can be supported on a ledger and single 2x8 beams resting directly on corner footings. If any dimension is substantially longer, double the 2x8s—either by bolting one to each side of posts or butting them together on top. For drainage, butted beam planks should be separated by spacers—3" squares of 1/4" thick plywood—where they are affixed to posts and nailed in every 2'. Butted 2x8s with spacers will fit neatly atop a 4x4 post.
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