A Deck for the Decades

Article Tools

Image Gallery

Print

E-mail

Comments

RSS

THE FINISHING TOUCH: DETAILS

The Frame-Up

Most people think of the deck framing as the platform itself, but where it's really happening is underneath the planks. The framework is the skeleton of the structure, and, like the bones of the body, it determines what the surface will look like.

If, for example, straight planking doesn't suit your taste, you might prefer a herringbone or alternating pattern. But you've got to know in advance how far apart to space the deck joists (the ribs that hold the platform "skin" in place) to determine how wide to make each section. Joists spaced 16" or 24" on center are common; 12" to 16" spacing is needed when 1-by (3/4" thick) or any diagonal decking is used.

My code book says that decks "shall be designed for a live load of 40 pounds per square foot"--the same figure given for house floors. (Decks larger than 100 square feet are boosted to a 60-psf limit.) Live load is the weight of everything but the building materials themselves; to put things in perspective, a 10' X 10' deck should support two well-distributed tons, or twenty-five 160-pound friends standing roughly shoulder to shoulder.

If you take a look beneath your house sometime, you'll see what that means in lumber: a line of 2 X 10s fastened between a rim joist and a girder or another perimeter joist. By the same method, 2 X 8s would more likely represent a 30-psf capacity.

How those boards are put together is a whole different story. The conventional method is to frame the entire platform with a doubled 2-by perimeter and hang the joists in between. They can be nailed to the rims on a ledger strip or connected with galvanized-steel joist hangers.

In some situations, the joists might rest on a girder made of two 2 X 10s fastened side by side. This beam doesn't necessarily have to be at the unattached end of the platform but can be positioned back by several feet so the deck is cantilevered slightly. Usually, it's set parallel to the end of the platform, with the joists running across it.

The part of the perimeter connected to the house--the ledger beam-may be the most critical member of the framing. That board must be pressure treated for aboveground use, and unless the band on the house is treated, it also has to be covered with flashing to keep water away from the unprotected wood. If the ledger is attached to masonry or concrete, it should be treated for ground-contact use but doesn't need a flashing.

Be aware that many building codes require that, when connected, the deck and structure beams touch each other, with no siding or blocking in between. That ledger beam is bolted to the house with nuts and washers, their size and spacing being determined by the joist span.

RSS | Comments | E-mail | Print