Engineered Wood Siding in St. Louis

How treated engineered wood is made

LP describes its process this way: the wood strands or fibers are treated with adhesive resins, water-resistant waxes and zinc borate, a preservative, so the treatment runs through the board rather than sitting on its face. A water-resistant, resin-saturated overlay is then bonded to the surface, and the boards ship either primed or prefinished. The company says it has run outdoor exposure tests near Hilo, Hawaii, a hot and very wet climate, starting in 1996.

The result is lighter than fiber cement. LP's catalog lists its 3/8-inch lap siding at 1.5 pounds per square foot in 16-foot lengths, against 2.31 pounds per square foot on James Hardie's fiber-cement specification sheet. LP's lap instructions allow its 38 Series directly on studs up to 16 inches apart and its 76 Series up to 24.

It is not the hardboard of earlier decades. Hardboard is wood fiber bonded under heat and pressure, a different product, and certain hardboard products drew class-action suits. Some city rules still lump the two together, which matters in Kirkwood (below).

Engineered wood or cedar

Cedar is the real thing. The residential code counts the heartwood of cedar and redwood as naturally decay-resistant wood; the sapwood does not get that credit. The USDA Forest Products Laboratory's Wood Handbook is blunt about leaving it unfinished: weathered wood erodes, splits and grows mildew in most North American climates. Only all-heartwood boards of a decay-resistant species such as western redcedar avoid decay that way, and they should be vertical grain to limit splitting and cupping.

Finished cedar needs upkeep. The handbook puts one coat of semitransparent stain on new smooth wood at 2 to 4 years, while two coats on saw-textured wood may last 10. It recommends back-priming siding before it goes up, which cuts water absorption and cupping, and sealing every end cut. Building America's guidance calls stainless steel nails the best choice, especially under a transparent or semitransparent stain.

Engineered wood trades some of that character for consistency: uniform boards, 16-foot lengths, factory treatment and primer. It cannot be stained, though. LP's instructions rule out stain and vinyl-based paint, so if you want a stained, natural-wood wall, cedar is the choice.

Paint, edge sealing and upkeep

Primed engineered wood is not finished siding. LP's instructions call for painting every exposed surface, including the drip edges where water hangs, with a high-quality 100% acrylic exterior paint made for wood and engineered wood. Oil paint is acceptable; stain and vinyl-based paint are not. The paint goes on as soon as possible and within 180 days of installation.

Gaps get a paintable sealant that meets ASTM C920, Class 25 or better, and painting exposed nail heads is recommended. Prefinished boards skip the site painting and carry their own finish warranty, but still need every cut sealed.

After that, upkeep is ordinary repainting on the paint maker's schedule, keeping caulked gaps intact, and keeping sprinklers and mulch off the bottom course.

Moisture and ground clearance

Wood-based siding fails from the bottom and the edges, so clearances matter more here than for vinyl. The code's general rule, IRC section R317.1, is that wood siding, sheathing and framing closer than 6 inches to the ground, or closer than 2 inches to concrete steps, porch slabs and patios, must be naturally durable or preservative-treated wood.

LP's instructions set their own minimums for its treated boards:

• 6 inches above finished grade, measured from the ground cover, so mulch counts;
• 1 inch above porches, patios, balconies and walks, which can drop to 3/8 inch only where the surface drains water away and is covered by a roof;
• 1 inch above roofing, with kickout flashing at roof edges that meet a wall and the siding kept out of the kickout and the gutter;
• 1 inch between the end of a gutter and the wall.

The same instructions require a water-resistive barrier, flashing that will last at least 50 years, and no installation over rain-soaked or buckled sheathing. St. Louis County's own code table rates termite risk here as slight to moderate, one more reason to keep wood off the soil.

Installation details the warranty depends on

LP's lap siding instructions state that not following them makes the limited warranty inapplicable to the boards affected. The details worth checking on your job:

• Nails. Hot-dip galvanized, at least 0.092-inch shank, reaching 1-1/2 inches into studs or sheathing and studs combined.
• Placement. Blind-nailed 3/8 inch from each end and at least 3/4 inch below the top edge, with courses overlapping at least 1 inch.
• Order. Nail from the center of a board out, or from one end to the other, never from both ends toward the middle.
• Depth. Heads snug, not sunk. A blind nail countersunk more than 1/8 inch has to be re-nailed.
• Butt joints. A 3/16-inch gap finished with sealant or a joint molding, or left open over 4-inch pan flashing.
• Trim. A 3/16-inch gap where siding meets window and door trim, sealed.
• Flat walls. Shims at the studs so boards are not pulled against an uneven wall.

On storms: LP's catalog says its limited warranty covers hail damage up to 1.75 inches in diameter. Read the exclusions, and see hail damage to siding for how claims play out here.

Where engineered wood is discouraged

Kirkwood is the place to check first. Its architectural guidelines, which the city code applies to exterior renovations as well as new houses unless the work is on an exempt list, put engineered wood siding, naming OSB, hardboard and plywood, on the discouraged list. Discouraged does not mean banned. It means the review board is less likely to approve it and the owner has to show how it fits the neighborhood. Wood or fiber-cement clapboard is on the preferred list.

Historic districts can go further. In the City of St. Louis, Shaw's standards bar siding of any type, and each district has its own rules; see historic districts. In St. Charles, the preservation article says deteriorated historic features get repaired instead of replaced, and a replacement must match the old one in design, color and texture, and in material where possible. Original wood siding there is a repair-first job.

Permits differ too. Unincorporated St. Louis County names wood and hardboard on its no-permit siding list, while the City of St. Louis exemption covers only aluminum, steel and vinyl. Check your city on our permits page.

Cost: what we can and cannot tell you

The 2025 Cost vs. Value Report prices only vinyl and fiber-cement re-sides, not engineered wood or cedar, so there is no independent regional figure for either one, and we will not make one up. For orientation, the same report puts a 1,250-square-foot re-side in this region at $18,907 in vinyl and $23,470 in fiber cement.

What moves an engineered wood price:

• primed boards painted on site, or prefinished boards with a factory finish;
• lap, panel or shake profiles, and the trim package around openings and corners;
• how much shimming an older, uneven wall needs;
• rotten sheathing under the old siding, billed at your estimate's square-foot rate;
• lead-safe set-up and cleanup if the house predates 1978.

For cedar, add the grade of the boards, back-priming, stainless fasteners and the finish you choose. Both come in writing on a free estimate. See siding replacement for how the job runs.

Common questions about engineered wood siding in St. Louis

Where we work

Engineered wood siding across greater St. Louis, from the city and St. Louis County out to St. Charles, Jefferson and Franklin Counties and across the river into the Metro East. Each city has its own page with the permit rule and code edition that apply there: