Landscape Architect Articles

Pressure-Treated Wood Put to the Test in High Sierras09-14-09 | News

Pressure-Treated Wood Put to the Test in High Sierras

The 1,300 feet long Tahoe Meadows Boardwalk is constructed with alkaline copper quaternary (ACQ) pressure-treated (PT) Douglas fir to protect against termites and rot. PT wood was tested and chosen over composite and recycled plastic for its natural look, ease of installation, ability to withstand foot traffic and stand up to the Sierra?EUR??,,????'?????<

When Jeremy Vlcan of Beneficial Design, Inc., Minden, Nevada, was awarded the contract to construct a 1,300-foot section of boardwalk at an elevation of 8,000 feet in the Humboldt-Toiyabe National Forest of the Sierra Nevada, he recognized some impressive challenges.

The boardwalk had to be aesthetically pleasing and fit in with the beautiful surroundings. The material choice was critical. The boardwalk had to withstand the foot traffic of thousands of visitors, plus survive the 25-foot snow pack of the high Sierra winters.

?EUR??,,????'?????<

The copper and quaternary compounds protect against fungi, termites and general rot and decay. The preservative injected into the wood forms an ?EUR??,,????'?????<

Environmental restrictions required the 50 tons of Douglas fir lumber be wheel barrowed into the build site. Pylons or concrete footings were not allowed. The boardwalk foundation was four-by-six-by-one-foot footing blocks on the ground anchored with one-quarter-inch diameter, 30-inch long rebar. The required elevation for the boardwalk was 20 inches, two inches above ADA guidelines.

Enviro Issues

Environmental regulations dramatically impacted installation by prohibiting the use of motorized construction vehicles! The construction team thus had to carry 50 tons of pressure-treated Douglas fir by wheelbarrow to the build site during the nine-day installation.

?EUR??,,????'?????<

He notes that drilling the pilot holes, final holes and making structural cuts was faster and easier with the PT wood compared to recycled plastic or composite material.

?EUR??,,????'?????<

Because of its wilderness-sensitive location and for the safety of a broad range of visitors, the required elevation of the boardwalk was 20 inches, two inches above ADA guidelines. Six-inch toe rails are installed and braced every 12 inches, on both sides of the boardwalk.

Young, old or disabled can use the boardwalk. The ADA-certified tow-rail system doubles as a safety reminder for young children not to venture beyond the main boardwalk structure.

Environmental regulations in this sensitive wilderness forbade the use of auger pylon systems, heated coils or concrete footings. Footings for the boardwalk were constructed using one-half-inch rebar, 30 inches long. The footings, one on each side of the boardwalk and one in the middle, are spaced 20 to 24 inches apart, so that each 15-foot section of the boardwalk is anchored with nine footings per section. The 12 x 12 footings are fabricated with the same inventory of ACQ PT Douglas fir used for the toe-rail system and the primary boardwalk planking.

The foundation for the boardwalk is four-by-six-by-one-foot footing blocks on the ground anchored with one-quarter-inch diameter, 30-inch long rebar. Two rebar sections were drilled into each footing block at an angle to each other. The substructure comprises four-by-four-by 12-foot and four-by-four-by-six foot pressure treated Douglas fir. The walking surface is two-by-two-by-six-foot sections of PT Douglas fir.

The Tahoe Meadows Boardwalk is a reality thanks to the shared vision of the Tahoe Rim Trail Association and Jeremy Vlcan at Beneficial Designs. They collaborated and won a grant from the Nevada Recreational Trails Program to design and install the first section of boardwalk in the summer of 2008.

The new boardwalk protects the meadow grasslands and a creek bed and should remain serviceable for many years under extreme climates and heavy seasonal use. Jeremy Vlcan, and now Eric Glass, along with their Tahoe Rim Trail volunteers, is submitting a new grant application in 2009 to extend the Tahoe Meadows Boardwalk further into the meadow.