Sistered Joists Invite Rot

I would like to comment on Mike Guertin's suggestion to use "sister" joists to stiffen up a bouncy deck (Question & Answer, Jul/Aug 07). As a former remodel and repair contractor, I've repaired a number of decks. My experience convinces me that sistered joists — unless done correctly — are an invitation to structural failure.

The problem is that moisture gets in between the two joists and doesn't dry out. Rot quickly sets in, and the side-by-side joists soon turn to mush. Every time I've repaired a deck with sistered joists, they have been rotted, while single joists have typically fared much better.

Caulking the top of sistered joists may delay decay but probably will not ensure long-term protection. Inserting new joists halfway between the existing joists may work. The use of pressure-treated joists is a good solution, but good-quality, straight PT stock is not always available. (Few decks here in the Southwest are framed with PT lumber).

If you must sister joists, I recommend using 1/2-inch spacers to separate them (1/2-inch nuts on staggered carriage bolts work well), creating an air space that allows drying between the joists.

Mike Davenport

Flagstaff, Ariz.

Mike Guertin replies: That was my omission — my experience is east of the Rockies. A small (and increasingly disappearing) number of decks here are framed with untreated lumber, and the treated southern yellow pine we use generally accepts chemical treatment far better than does the incised and treated hem fir and Doug fir used in the West. You're correct that tightly sistering untreated deck joists, or those whose cores are untreated, will lead to decay. If the decking boards are being removed as part of the job, then the problem is easily avoided by capping the sistered joists with a waterproofing layer (Grace Vycor Deck Protector, Joist Jackets, York Shield 106, or strips of #30 tar paper) to keep water out of the joint. Your solutions would also work. In fact, I often space joists with 1/2-inch to 3/4-inch strips of PT wood ripped from scrap. I space them vertically 12 inches to 16 inches apart and through-nail. The lumber contact issue isn't just limited to sister joists, either; a built-up beam should also be capped to avoid rot problems when using suspect treated lumber, or if you want a bullet-proof job. Mike Guertin East Greenwich, R.I.

Feedback on Post Attachment

Regarding your article "Lab Testing of Single Posts" (Question & Answer) in the May/June 2007 issue, it is easy to pooh-pooh the cost of $200 when you are not the deck builder absorbing the cost. Also, the testers don't take into consideration — in addition to the rail cap — the horizontal 2x4s that are run across all the posts, continuously, to support the balusters, both top and bottom. That means the load, whatever it is, is divided over all the posts, not just the one that is hit. This wouldn't apply if the rail cap and shoe were toe-nailed, but it certainly applies if there is a 2x4 both top and bottom, which is still the strongest way to build railings.

Nick Breslin

Breslin Decks & Awnings

Jenkintown, Pa.

More on Cable Railings

I'm writing in response to the two defenders of horizontal cable railing in your July/August 2007 Letters column. Do we really need studies to confirm common sense? Are all unstudied activities safe by default? It seems to me that the disservice is not by your publication but by an industry eager to push a flawed design as long as possible. How hard can it be to accept the fact that any kind of horizontal railing is a bad idea?

Jim Gage

Eagle Construction & Remodel, LLC

Bothell, Wash.

Most of the argument that there is no statistical data to reinforce the danger to children from the "ladder effect" is advanced by manufacturers or vendors of products that would be affected by the outcome of the data. I have a deck store with 22 railing displays, and my three-year-old son spends a lot of time there. There is only one railing display that he climbs on, and it is the horizontal cable-rail display. I don't need any data to reinforce what my three-year-old knows instinctively.

Thomas R. Booker

President, The Deck Store



In the July/August 2007 issue, we list author Cheri B. Hainer ("New Ledger Attachment Requirements Adapted") as a code-enforcement official in Fairfax County, Va. Hainer is actually the Permits and Inspections Administrator (who also functions as a building official) for the City of Virginia Beach, Va.