Q: I’ve seen the Pylex powder-coated adjustable post base, which allows adjustment in elevation after install. This seems pretty convenient. However, are these ‘approved’ by most (or any) building codes? – Chief
A: I like stand-off post bases that hold the bottom of the post about an inch above the concrete pier (see photo), protecting the post from sucking up water through capillary action. In my experience, modern pressure-treated lumber is not as rot-proof as the older CCA-treated wood that was phased out during the early 2000s.
Many bases can be adjusted horizontally to help center the post correctly. However, adjustable-height bases, like Pylex Deck Support 66, are generally not allowed for permanent structures by building codes.
Adjustable support only. You will sometimes see adjustable steel columns with screw bases (also called” jack posts” or “screw jacks”) in basements supporting the carrying beam for the floor joists. Although most of these adjustable columns are designed only for temporary support, they are sometimes left in place permanently.
As to whether the building code will accept an adjustable-height base for a backyard deck, you would need to check with your local building inspector. Like many code questions, this would fall into a gray area, subject to local code interpretation. In general, however, screw-type hardware is best used for temporary support only.
I don’t see anything indicating that the Pylex product has this type of code evaluation report. They do caution “Please make sure that you observe all building codes in your area.” So it’s not likely to be accepted by your local code official.
Powder-steel coatings. The other concern for this and other home-center products is the powder coating vs. a heavy hot-dipped galvanized finish or stainless steel, the most expensive option. Powder coatings are mainly cosmetic and do not offer long-term protection from rust.
In addition, the current type of pressure-treated lumber is much more corrosive to metal than the older CCA-treated wood. Sitting under a pressure-treated post with water dripping down exposes the metal to a heavy dose of wood preservatives. For this application, I would definitely recommend a G-185 heavy galvanized coating such as Simpson’s ZMAX or USP Triple-Zinc. If you’re near salt water or are supporting a living space, I’d strongly consider stainless steel.
Take a look at this information sheet from Simpson Strong-Tie. You’ll notice that steel powder coating is listed as “low” in corrosion resistance. I’ve discussed this with the tech folks at Simpson who say that powder coating is fairly durable but is mainly for appearance, not for rust protection. Most powder-coated steel is not galvanized.
Even the manufacturers of powder coating do not recommend this as long-term protection from corrosion. According to coatings manufacturer Cadillac Coatings : “Once the protective powder coating has been penetrated, moisture is able to work its way under the finish and rust will begin to form. When left alone, rust acts like a cancer and will spread and slowly erode the finish. If a chip, scratch or crack is swiftly taken care of, the spreading of the rust will cease. ”
I recently built a screened porch with living space above. Not wanting to take any chances, I sprung for 6×6 stainless-steel post bases. These were over $100 each, but replacing them would have cost a lot more. For most decks and porches, heavy galvanized steel would be fine.
While adjustable-height bases is an nice feature, it’s not hard to line up the post tops. Just install your posts a little long, then snap a line and cut. No problem. – Steve Bliss, Editor, BuildingAdvisor.com