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Building Paper Under Vinyl Siding

After looking at picture D on page 24 of the February issue of JLC, I wondered why sheathing paper is not required under vinyl siding.

Bill Moyse Delhi, N.Y.


Editor Don Jackson responds: Though it's always been a good idea to use it, the IRC didn't require building paper under vinyl siding in earlier editions, allowing it an exemption in Table R703.4. However, that's been changed in the 2006 IRC: Vinyl, like other claddings, must now be installed over a "water-resistive barrier" (called a "weather-resistant sheathing paper" in previous editions).

Contradictory Advice?

Page 38 of January's JLC (Q&A, "Sealers for Porch Floors") states that "research has shown conclusively that solid wood products back-primed with a WRP [water-repellant preservative] retain paint better — and perform better overall — than those coated on one side only."

On page 26 of the accompanying Coastal Contractor [a supplement to JLC readers who live near the East Coast], the advice is exactly the opposite: "... one thing you never want to do is back-seal the bottom surface of any decking. The top surface will inevitably break down quickly due to UV exposure, and once it does, the wood will absorb water. If the bottom surface is sealed, the boards essentially fill up like troughs, hastening the deterioration of the remaining finish and the wood itself."

In my home-inspection business I frequently rely on information supplied by the experts and building scientists in your publications. Contradictory guidance is frustrating. It would be relatively simple for building scientists to compare notes or research and come to an agreement on a best practice for back-priming exterior decking.

Dimitri Ledkovsky Chapel Hill, N.C.

Editor Don Jackson responds: While a "one-size-fits-all" solution would be nice, in this case there isn't one. The two applications you refer to — a partially protected T&G Doug fir porch floor and an exposed coastal ipe deck — are very different animals. It's well established that it's futile to put a film-forming finish, like paint or a solid-color stain, on a wood deck: The finish will break down, allowing water to get into the deck boards but preventing it from easily getting back out, thus hastening the deck's demise. That's why the treatments most often used on decks are penetrating water-repellant preservatives, which help keep moisture out of the wood and resist UV degradation but don't form a film. All of these products have to be maintained with regular cleaning and recoating. How regular depends on many factors, including sun exposure, climate, type of wood, and how durable the finish product is. One of the beauties of ipe is that it weathers well without surface treatment, as long as the client doesn't mind the silver-gray color it takes on. The recommendation in the Coastal Contractor article not to seal the bottom of a deck, but to allow good air circulation, is consistent with what most deck-finish manufacturers advise. As for the traditional painted porch floor, Bill Feist's recommendation to seal all sides of each tongue-and-groove floor board is based on solid field evidence. The National Park Service has been using this method for many years when replacing porches and has found that it greatly extends the service life of the flooring by helping to prevent cupping and checking. It also makes the top coat last longer, for the same reason. The NPS is careful to use only one coat of primer, an acrylic, which doesn't completely seal the wood but allows water vapor to escape, thus allowing the porch floor to dry to the bottom if necessary. More specifically, Feist's recommendation to use a paintable water-repellant preservative for the prime coat is based on field-testing done at the Forest Products Lab, in which this type of product outperformed conventional paint primers on hardboard siding. Earlier work at the lab had established that exterior wood holds paint better if it's primed on all sides.

Quick Newel Layout Tips

I read the article "Quick Layout for Stair Rails and Balusters" (2/06) with great interest. I marveled at its simplicity and usefulness, but one thing caught my eye.

On the subject of shortening the newel, the example newel is a box type with a built-up base. So if you were to lay the rail on the tread nosing to mark the newel, you would not actually be touching the newel in the intended location, because of the 3/4-inch built-up base. In this case, the newel would have to be shortened more, because the rail line would extend further by the 3/4-inch thickness of the base while descending at the given angle of 37.3 degrees.

Daniel Gordon Franklin, Mass.

Author Phil Springer responds: You have a good eye. Yes, the mark would have to be adjusted to compensate for the 3/4-inch skirt wrap. This newel was purchased with the base wrap already attached, so after making my mark on the post while the rail was down on the treads, I referred to my full-scale drawing of the rise and run of the stair. I measured 3/4 inch back from the front (nosing) corner of the triangle and drew a line up perpendicular from the base to the hypotenuse to find the additional amount of height that needed to be cut off the bottom of the post. This amount can make a difference, as many newel posts don't leave much extra room for the rake cut of the handrail to land. Box newels take quite a bit of time to cut and fit well, and having to cut them off a second time gets expensive. Thanks for pointing out this potential time-waster. I'd be lying if I said that I've never made that mistake before, but the days you don't get richer, you get smarter. Now I generally remember to cut the extra length off the first time.