Q. I was hoping someone could shed some light on EB-TY. I use this product on 80% of the decks I build, and many are one or more stories high. I also live in a heavy snow area. The clips in that system hold the decking to the framing with pressure, not with mechanical fasteners, and I'm concerned that the detail may not be strong enough. I have been taking extra steps by letting cross bracing into the joist system. Am I wasting my time?

A.Frank Woeste, P.E., professor of wood construction and engineering at Virginia Tech University in Blacksburg, responds: You certainly are not wasting your time to be cautious in building a deck. Like roofs, decks don't experience their full design load (such as a heavy snowfall or a large party) every day or every year. But you must build them to handle that extreme design load when it does occur, because a failure can be catastrophic (see " Deck Disasters Spotlight Faulty Connections," Notebook, 9/02).

I don't know of any engineering numbers on the type of fasteners you're talking about, but they may not be designed to resist the forces a deck can experience. And we haven't had 40 years of experience with the product to learn from, as we have with traditional 8d or 10d threaded nails that would typically be used with 5/4 decking boards. It's safest in this case to disregard any bracing effect of the decking and fasteners and build the structure to stand up without them.

However, the diagonal let-in bracing you mention, whether it's installed within the floor frame or between the posts and the deck framing, probably is not going to do the job. There are two important issues to consider: twisting of the deck joists and racking of the deck in plane. Even with the joists secured against any rotation at each end, they'll tend to twist within the span when a load is placed on top if they're not restrained somehow. Assuming no help from the decking, you'd be wise to install PT solid blocking at 2 feet on-center. That probably sounds like a lot to most carpenters, but that spacing is borne out by experience with long-span truss chords that are held with 2x4 purlins at 2 feet on-center. If you wanted to space the blocking farther apart, you'd need engineering for the specific span, joist spacing, and lumber size, grade, and species.

As for racking, one solution when earthquake loads aren't involved is to firmly attach the deck to the house and to its carrying posts (which should be minimum 6x6 posts treated for a structural application in ground contact) and to embed the posts firmly into the earth at least 3 1/2 feet deep. Then the supports can hold the deck in place without the need for racking resistance from the deck boards in the plane of the deck itself. However, diagonal bracing of the posts might be required to "stiffen" the system, depending on deck height, post size, and deck size.