Sturdy joinery and durable materials
form a new deck and bridge
by Gene DeSmidt
Fine HomebuildingTassajara project page
July, 1991 No. 97
15 years ago, during a West Coast trek, I walked into Tassajara Hot Springs through massive wood gates hinged to a log-framed, Japanese-style entry. The entry's concrete and stone foundation seemed to grow right out of the ground. Huge boulders were strewn about, each appearing to be purposefully placed. Surrounded by native pine, oak and sycamore, they offered a serene welcome to a weary traveler.
Since then, I've returned to Tassajara dozens of times to orchestrate a variety of construction projects as a breather from my hectic contracting business. This article will focus on one of my favorites: the rebuilding of a wood bridge that spans a creek and provides access to Tassajara's 110 degree Hot Springs, as well as the rebuilding of an accompanying deck. The project called for the construction of nifty details such as mortised-and-tenoned railings, bamboo-covered screens and gable-roof entries. Everything was built to endure high water, damp, cold winters and bone dry summers, and called for a degree of craftsmanship befitting the location. Of course, that meant living in this remote paradise for the duration of the job, or about six months. That was a sacrifice I could live with.
Bridge building - Tassajara is a Zen Buddhist monastery/Hot Springs resort, known in part for its vegetarian cooking and books on bread, as well as for its attraction to professionals and crafts persons in need of a respite. Located in remote and rugged canyon about 30 miles east of Big Sur, it's reached by driving over a steep, bumpy, 15 mile-long dirt road.
Our daily routine began with bells and breakfast and a morning meeting not unlike what might have occurred in an ancient craft guild, or even a modern small town factory. Then we went to work.
Because the existing bridge was a safety hazard, we started there. Built in 1969 as a temporary replacement, it's back bone was a pair of 35 ft. long girders, laminated on site by bending Douglas fir 1x4s around a tree and nailing them together. Untreated, the girders had rotted beyond repair. The new bridge is supported by a pair of laminated pressure treated 8x18 Douglas fir girders, cambered 2 ft. for a traditional appearance. They were designed by Paul Discoe of Joinery Structures in Oakland, engineered by Geoffrey Barrett from Mill Valley and custom-made by Barnes Lumber, a truss manufacturer in Cloverdale. The girders were trucked to Tassajara on a 24 ft. flatbed.
We began demolition and construction in late summer, when the river was low. We started by cutting down the old bridge with chainsaws, letting it sit temporarily beneath the location of the new bridge to serve as a scaffold. Then we built a simple dolly to support the leading ends of the girders, screwed 2x handles to their trailing ends and (with the help of then people) rolled the unwieldy monsters across the old bridge, one at a time.
The next step was to bolt the new girders 4 ft. o.c. to a new redwood "trestle" on the bathhouse side of the river and to an existing concrete foundation on the opposite side. The trestle consists of two built-up 61/2-in. by 71/2-in. posts capped with a 6x14 beam and braced diagonally with a pair of 2x6s. The posts are planted in a reinforced-concrete foundation to which they're pinned horizontally with 1/2 inch stainless-steel threaded rod.
With the girders anchored, the next step was to tie them together and to fasten 4x4 railing posts to their outside faces on 4-ft. centers. We accomplished this both at once through the use of 1/2 inch galvanized threaded rod.
The technique was simple. First, we marked the locations of the railing posts on the girders and tacked 4x4 cleats vertically to the inside face of the girders directly opposite the layout marks. Next we nailed 40-in. long, 2x12 spacer blocks to the 4x4 cleats. Posts were then installed in opposing pairs by running a single length of threaded rod through both posts, both girders and the two corresponding 4x4 cleats. We used hex nuts and malleable washers to simultaneously tighten the posts against the girders and the girders against the 2x12 spacer blocks (malleable washers have a larger diameter, for more bearing, than standard washers, and we liked the way they look). Finally, to prevent the bridge from swaying, we installed 2x6 diagonal bracing in each 4 ft. section.
Fitting the railings - between the posts, the bridge railings consist of 2x2 balusters spaced 6 in. o. c. and mortised into 2x4 top rails and 1 1/2-in. by 3 1/4-in. bottom rails. The top rails sit atop the posts, while the bottom rails are mortised into them. We cut the mortises, using a router equipped with a straight bit, and the tenons with Japanese handsaws. For a decorative effect, we turned the balusters 45 degrees to the rails (we called them "diamond pickets").
Up top, we dadoed a 1 1/2-in. by 4 1/4-in. railing cap to slip over the top rails. The ½-in. deep dado rendered the cap flexible enough to follow the curvature of the bridge, disguising the straight lengths of the top rails. The dadoes were cut using a Makita groover, a handy tool that resembles a power plane equipped with dado knives (unfortunately, Makita doesn't sell them in the US).
We used Port Orford cedar for the railings (and for most of the other woodwork on the site). It's a fragrant rot resistant, exceptionally stable wood that's used for everything from closet linings to canoe paddles. The wood is native to southern Oregon and Northern California but it's in such demand in Japan that it's becoming relatively scarce and expensive in the US. We bought ours from a small mill in Oregon and had it trucked directly to the site.
We prefabricated the balustrades in sections by screwing the top and bottom rails to the balusters with 2 1/2-in. long galvanized drywall screws. That made it easy to install the sections between posts as we worked our way across the bridge. We screwed the top rails to the tops of the posts with drywall screws and, once all the sections were installed, fastened the caps from underneath the top rails using 2-in. long galvanized drywall screws, shimming the caps where necessary to follow the camber. Finally, we chamfered and planed the caps to a glasslike finish using Japanese hand planes.
With the railings completed, we screwed 1x2 cleats to the top outside edge of the girders. Then we screw to random-width, 2 x cedar decking to the cleats from below so that no screws would show on top. The New bridge was finished with Penofin (Performance Coating Inc). before we completed the demolition of the old one. We chose Penofin because we like the Golden Tone it imparted to the cedar.
Fixing the underpinnings - a year before replacing the bridge, we had excavated and poured continuous 24 inch buy 12 inch deep concrete grade beam in line with andbeneath existing concrete deck columns. the grade beams were designed to prevent the columns from being undercut by the river's current and to buttress them against careening boulders.
Now that the new bridge was completed, it was time to tear out the old deck, beef up the battered columns and build a new deck. We enlarged the 8x8 columns to 12x12s by wrapping a cage 1/2 inch Rebar around each one enclosing the cages with forms built out of three-quarter inch plywood and 2x4s, and in filling the forms with concrete. The columns are capped with stainless-steel brackets (custom-made by Stoltz metal in Oakland) secured with anchor bolts set into the concrete.
With the columns repaired, we bolted a series of 6x12 pressure treated girders to the stainless-steel brackets parallel to the river. Then we installed 4x8 pressure treated joists perpendicular to the girders on three ft. centers, sufficient to support the covered benches, privacy screens and other structures that would eventually sit on top the deck.
The joists are supported at the girders by joist hangers, and at their their opposite ends by pockets cold chiseled out of the concrete foundation supporting an adjacent bathhouse. We installed the choice 1 1/2 inch below the tops of the girders so that the decking would be flush with the girders and nearly flush with the tile floors in the bathhouse.
The decking is 2x6 Port Orford cedar, fastened with 3 1/2 inch silicon bronze, ring-shank boat nails. These nails, which cost about 6 dollars a pound are very durable and hold so tenaciously that they're almost impossible to pull out without destroying the wood in the process. I bought ours from R. J. Leahy & Co. in San Francisco.
To widen the walk at the front of the deck, we also installed one deckboard on the outboard side of the girders. This was accomplished by nailing 4 x blocks to the front of the girders on three ft. centers, nailing a 2x12" cedar skirtboard to the blocking, and installing the deck board over the blocking and skirt board. The skirt board conceals the face of the girders.
Bamboo for privacy - the design of the deck top, including the layout of the railings, bamboo covered privacy screens and covered structures, was primarily the handiwork of Berkeley architect Mui Ho. Many of the structural and visual details, however, were worked out on site by me and my crew.
The deck railings mimic those of the bridge, except for a few details. The top and bottom rails are both mortised to the posts and are 3 inch wide; the rail caps are'nt dadoed on the bottoms; and the rail posts are fastened with 1/2 inch lag screws and malleable washers to the skirt boards and girders.
The bamboo covered screens are framed with 4x4 posts and spaced 4 feet o. c. and capped with 1 3/4 inch by 4 1/4 inch top rails, both dadoed to receive 1/2 inch marine great plywood panels (bottom drawing facing page). The screens at the front of the deck were installed by lag screwing the posts to the skirt board, same as the railing posts. We wanted the rest of the screens to appear as though they were freestanding, with the posts simply sitting on the deck. We accomplished this by mortising a series of 2 1/2 inch square holes in the decking to except 8 inch long tenons cut on the bottom of the posts. Every third tenon was fastened directly to a deck joist with two lengths of 1/2 inch galvanized threaded rot. The remaining tenons were sandwiched between and bolted to a pair of 2x6 blocks installed perpendicular to the joists. We cut the mortises using a jigsaw, and the tenants by making several passes with the circular trim saw and knocking out the waist with a hammer and a woodblock. The tenons were cleaned up using a razor sharp slick.
Before installing the plywood panels, we soaked them with the water repellent preservative and painted the interior faces facing the bathhouse with an off-white exterior latex paint. Then we slipped them into their dadoes and toenailed them to the posts through their exterior sides. We stapled bamboo reed (bamboo strands woven together with galvanized wire) over the exterior sides of the panels, trimmed the exterior sides with 1x2's, installed with a nail gun, and applied Penofin to the cedar.
As soon as we installed a section of the screen, we found that its six-foot height was too short to block the view fully from the apex of the bridge. Because post height was limited by the length of our stock, our solution was to dado 1x8 Western red cedar panels into the top rails and to cap the panels with dadoed lengths of 2x3 in. Port Orford cedar beveled to a peak on top. Every 8 ft. to 10 ft., we lag-screwed a short, dadoed 3x3 post to the top row directly over a 4x4 post to support the ends of the 1x8 panels. The solution worked and added a nice decorative touch to the top of the screens.
Posts and beams - in all, the deck supports five gable-roofed structures: one highlighting the entrance to the bathhouse complex; two serving as entries to men's and women's bathing areas; one each for a storage shed and the women's shower. The shower and storage shed were stick-framed and stuccoed, while the remaining structures were framed with Port Orford cedar posts and beams.
Each post and beam structure consists of 4x4 posts fastened to the deck in the same way as the screen posts. Above, the posts are mortised into a continuous 4x beam that supports the roof. We lap-jointed and screwed the beams together at the corners, allowing the two beams that support the rafters to cantilever past the post to carry the roof overhangs.
The 3x6 rafters were cut like typical common rafters. To install them, we toe nailed them on 2 ft. centers to the ridge beams through the tops. Then we drilled the 9/16 in. hole clear through each rafter pair and the ridge. That allowed us to insert a length of 1/2 inch threaded rod through each hole and to tighten the rafters against the ridge with hex nuts and washers. The nuts and washers were countersunk to prevent them from protruding above the rafters. We screwed the bottom of each rafter to the supporting beams with a 1/2 inch lag screw.
The system of attachment strengthened the roof framing markedly even before we nailed down the 1x6 Western red cedar roof decking. Once we installed the decking, we finished the roof with 15 pound felt and 30 year fiberglass shingles. For a decorative touch, we chamfered most of the edges of the framing members with the router.
The walls of the men's and women's entries are of the same construction as the bamboo screens, except instead of painting the interior side of the 1/2 inch plywood, we covered them with Western red cedar 1x6s, chamfered on the edges and fastened horizontally. The Neapolitan colored Western red cedar contrasts nicely with the Port Orford cedar framing. They entries were finished with Penofin.
Chiseling the steps - To reach the ancient steam rooms from the deck, bathers used to have to slip and stumble over an awkward set of river-rock steps. Feeling strongly that this invited a broken ankle or worse, I commissioned San Francisco sculptor Robert Gove to carve a set of solid sandstone steps to replace the old ones.
The new stone steps not only look good, but their naturally rough texture makes them virtually slip proof (a concrete-filled copper handrail was installed later).
Setting the last step provided the finishing touches on the bathhouse project. The now completed bridge, deck and stairs were ready for the pleasure of the Tassajara guests and resident bathers.
Gene DeSmidt is a contractor in Oakland CA.