APA reins in moisture with headquarters revamp

By Kevin Hayes APA-The Engineered Wood Association

THE international headquarters for f APA-The Engineered Wood Association in TacJma, Wa., underwent an extensive exterior makeover recently as 25-year-old panel siding was replaced with engineered wood lap siding.

"We tackled the residing project like one of our research projects," said Ed Keith. Technical Services Division senior engineer. "Our ultimate goal was to improve our building envelope performance by incorporating better construction details and products that protect against moisture intrusion."

As an accredited research lab and wood products certification agency. the association is considered the voice of the engineered wood products industry. If the association is the voice, then its headquarters is the face and that face needed a lift after years of exposure to famous Northwest rain.

TO PROPERLY seal the gaps and joints, APA turned to DAP's polymer-based SideWinder sealant due to its liletime guarantee and workability over wet lumber and metal. The product was applied by pushing the bead into the gaps rather than pulling down as many professionals do.

The five-story, 35,000-sq. ft. building was originally sided with channelgrooved kerf-sawn panel siding. The siding held up reasonably well considering design encumbrances such as a lack of overhangs, deep set window bays, and minimal flashing and caulking materials used on openings and wal I -to-roof intersections.

"Building designers and contractors knew little about moisture transmission science when the building was originally constructed," said Keith. "Contractors put up the building the way it was designed, applied the building paper and flashed the windows, and that was about it for moisture details."

Keith noted, "The parapet surrounding the flat roof is over 40 feet from the ground. The walls of the building acted essentially like giant wooden sails collecting wind-driven rain in every unprotected crevice, crack and joint."

FACTORY-PRIMED LP SmartSide engineered wood lap siding boards-7/16"x6"x16'-were spaced 1/4" at the butt joints to allow for-expansion and cohtractio'n. Normally, 3/16" space ts recommended, but due to the long length of the siding boards and the 125' building length, the additional width was required. Long lengths minimize the number of seams.

The result: moisture intrusion on the western and southern faces of the building (the direction of the prevailing wind), a problem exacerbated by the subsequent invasion of ants and termites.

APA's research into moisture control construction practices began years ago, culminating in 200 I with the development of a comprehensive moisture-training program identified as the Build a Better Home program. This program, with over 30 moisture control details for wall construction, served as the basis for its own makeover.

The six-week renovation included tearing off the existing siding, inspecting and treating for moisture and insects, replacing worn framing and sheathing, installing a shinglelapped Typar membrane. taping membrane overlaps and edges, installing polyethylene corner and starter strips, applying a Home Slicker rainscreen. flashing window openings, affixing new powder-coated metal window pans, installing LP SmanSide lap siding and trim, priming all cut edges, caulking joints, and painting the exterior siding and trim with two coats of acrylic latex paint.

In the fall of 2004. APA selected

United Roofing & Siding, Vancouver, Wa., a contractor with a track record in remedial moisture control and construction. They understood the science behind moisture intrusion. and were willing to experiment with materials and ideas that APA brought to the project.

The project's initial phases involved careful evaluation of the existing 1/2" plywood sheathing. In all, roughly 2O7o of the old sheathing was replaced, including all sheathing that framed the window bays.

At inside and outside corners, APA suggested a new twist on an old detail to prevent wind wash-wind pressure behind the siding driving the winddriven rain around the corner. Polyethylene strips were fastened on both sides of each inside and outside corner, on each wall. The rainscreen was then butted up to the 3"xll4" strips. This permitted each of the enclosed air spaces formed by the screen to act as a "chimney," explained Keith. "The poly strips would give us a waterproof dam at these critical junctions."

Not unexpectedly, the 75 window bays and other wall insets received fastidious moisture control detailing. The vertical and horizontal plywood surfaces in each inset were flashed with a rubberized asphalt membrane backed by a layer of high-density cross-laminated polyethylene. Housewrap was lapped shingle style over the membrane and up the sides of each bay followed by a layer of rainscreen. Horizontal surfaces received new, powder-coated metal pans while the sidewalls and tops were finished with5/8"resawnTl-ll.

With far greater emphasis on moisture control details and carefully selected products to protect and seal the building envelope, APA is confident that the building will look as good on its 50th birthday party as it does today.