Building Safer Decks

The prescriptive building codes are moving in the right direction, but some confusion remains

New in the 2009 IRC is a prescriptive table for lag-screwing and bolting ledgers to the house’s band joist. A similar table first appeared in JLC in March 2004. Note the third line of the schedule, which allows for a 1/2-inch drainage space to be used behind the ledger.

Because a doubled joist that supports other joists transfers a concentrated load to the ledger, it will require support beyond the code's bolting schedule. Some inspectors will make an exception for a small stair landing, while others will prohibit all beams from loading at the ledger.

In previous editions of the code, rails would not have been required on this deck — even though there’s an obvious fall hazard — because the grade directly next to the deck was less than 30 inches below the decking.

The 2009 IRC closes this loophole, requiring that the "landing" area extend 36 inches from the edge of the deck.

When this deck was built under the 2003 IRC, the slanted benchback, which is 24 inches tall, was considered a compliant guard.

Under the 2009 IRC, the back of this bench would have to rise 36 inches above the seat.

Although this bench seat is higher than 30 inches above grade, the deck's walking surface is not, so no guard is required.

A new controversial anchor detail is now "permitted" — though not explicitly required — under the 2009 IRC, and has raised inspectors' awareness of lateral loading issues. From a practical standpoint, installation may be difficult in existing homes because the tight subflooring nailing schedule would likely require ripping up the finish flooring.

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