Monday, January 16, 2017

THE PERGOLA: Made in the Shade

California architect Bernard Maybeck was
a master in building with wood, and nowhere
better than in the pergola structure of his
famed First Church of Christ, Scientist,
Berkeley.
I always get a blank look when I mention the word “pergola”.  A few people have even accused me of making it up.  Honest—I didn’t.      

A pergola is an outdoor structure that has two parallel rows of columns supporting a system of open roof beams. It’s more permanent than a trellis, arbor, or espalier, each of which is generally just a flimsy framework for plants to climb on. It's also a less formal structure than a gazebo, which usually has a radially symmetrical plan and a pitched roof.

I know it's January, but if you get started thinking about your pergola now, you can have it all finished and ready for summer.

Craftsman-era architects such as Bernard Maybeck and the brothers Greene well knew that a pergola extending from the house into the garden softened the transition between indoors and out, as well as providing a sensual respite from the hot sun. And indeed, on a hot summer day, a stroll beneath a graceful pergola overgrown with fragrant vines can be a memorable experience.


Stout columns with recessed panes are paired
in this handsome and unusual pergola design.
(Courtesy GardenStructure.com)
Since the pergola consists only of columns and an open roof, it’s also a delight to design and build. It has only two functional requirements: To provide shade for humans, and to provide support for climbing plants. The rest is up to you. 

The pergola’s columns should be substantial and not spindly—4x4s, for example, will look like toothpicks in the scale of the outdoors. While you can of course use off-the-shelf classical columns, it’s a lot more fun to come up with your own design. Try experimenting with hollow box columns, building them up to a substantial girth out of stock lumber. Because there’s so little actual material in these columns, you can lavish great detail on them at modest expense. Try adding moldings or decorative motifs, ceramic tile accents, or materials such as iron or copper.  You can even incorporate lighting fixtures if you want to get fancy. 

 Heavy timber makes for a pergola that's both better looking
and more resistant to the ravages of weather.
(Courtesy of deedsdesign.com)
The pergola’s columns usually carry heavy primary beams, which in turn support a secondary set of smaller beams at right angles to them.  If the primary beams run crosswise, the pergola’s width will be emphasized; if they run lengthwise, its length will. Both primary and secondary beams can be cantilevered (extended beyond) the columns, and they can be finished with decorative end cuts such as Maybeck’s trademark “dragon’s mouth”.  Again, the heavier the lumber, the better. Avoid using skimpy  members such as 2x4s, since they look insubstantial outdoors and will quickly warp and fall apart. 


Long curving pergola—this one in Berkeley's
municipal rose garden—invites strollers to explore.
(Berkeley, as you can see, is a sort of pergola nexus)
Finally, a network of spaced wood members—that is, some form of latticework—is usually placed on top of the secondary beams. Although redwood lath is often used, it’s really too flimsy to hold up under the summer sun, and will warp and split after only a few seasons.  Try  1x2 or 2x2 redwood instead, and to lessen the chance of warpage, screw the pieces down rather than nailing them.  

The topmost members are usually installed “self-spaced” (having a gap equal to their own width between them).  This provides a nice dappled mixture of shade and sun, and allows climbing plants to get a good grip.


A simple two-column pergola turns an
ordinary gate into a genuine entrance.
(Courtesy deedsdesign.com)
California redwood is the customary lumber for building pergolas. You can also use pressure-treated ("Wolmanized") Douglas Fir, which is much more affordable, if you don't mind the visible needle marks in the surface. If you feel guilty about using redwood for environmental reasons, as I sometimes do, console yourself with the fact that a well-designed pergola such as yours may well last half a century or more. Many of Bernard Maybeck’s already have.

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