Garden houses of closed top construction are preferable to those of the pergola style within the garden. Pergolas used in the garden should be treated as terminal features (Fig. 148) or as covering walks leading to substantial terminals. Then the lights and shadows from the overhead construction (Fig. 149), with its covering of Roses and vines,, are very delightful.
Pergolas may be of wood, brick, stone or concrete construction, depending largely on the style of the garden enclosures, architecture of the house, and the design and general surroundings of the garden.
Pergolas built of wood may be of a rustic nature, using wood with the bark on, or constructed of planed wood, stained or painted.
For pergolas of a rustic nature Red Cedar is the best material to use. For those constructed with planed wood, White Pine or Cypress are best. The high cost of White Pine makes it almost prohibitive. California Red Wood and Douglas Spruce are suitable for this purpose. The cost of these latter two is more moderate than that of either Cypress or Pine.
If the columns are of wood they should be set in concrete (Fig. 150), first coating the wood that is imbedded in the concrete with a tar paint. If the posts are set in the ground, that part in the earth should always be coated with tar.
If rustic posts are used the bark should be stripped from their lower portions before placing them in the ground.
When setting posts in concrete, allow the concrete to come a little above grade (Fig. 150) with the top beveled so that the water can not seep down between it and the post.
Treat logs with kerosene, to preserve the bark and protect it against the ravages of borers, which tunnel under the bark and soon loosen it.
Pieces selected for the uprights should not be less than eight inches at the base, preferably twelve. Clearance space under the cross pieces should not be less than eight feet and the breadth from center to center of posts for this height, assuming a twelve-inch column, should be eight feet two inches, making the clearance between posts seven feet two inches, just ten inches less than the height.
Always avoid making the width greater than the height; for good proportion the reverse is always better.
Fig. 149. - The lights and shadows from the overhead construction of the pergola, with its covering of Roses and vines, is delightful. - See page 188.
If turned columns are used their height should be eight or nine times the diameter and the lintels should be of two three-inch by ten-inch pieces, notched over the cap. The rafters (Fig. 151) should be three inches by eight inches, notched over the lintels. For the better support of vines, additional pieces should be placed on top of the rafters, running at right angles to the same. These pieces may be one and one-eighth inches by two and three-quarter inches; or of shingling lath, planed down, which reduces them to about three-quarters of an inch by two and three-eighths inches. The rafters (Figs. 151-153) should have a projection of from eighteen inches to thirty inches and should be cut to a good bold outline.
The caps should always be covered with light sheet lead (Fig. 151) neatly tacked around the edge.
When stone is used for the support of the superstructure the columns or piers should not be less than twenty-two inches, and these should stand on a foundation twenty-eight inches square, which will allow of a three-inch projection all the way around.
The stones should be laid up in cement mortar and, where pointed, the pointing should conform to the pointing of the house, if the pergola is adjacent thereto. An effective method of laying up the stone work is to rake out the mortar joints to a depth of two to three inches; this will give a deep shadow and form a friendly supporting ledge for the vines.
Cap stones should be of the same stone as that used in the piers, flat and hammer dressed, without projection, and set flush with the stone work below. It
Fig. 150. - Detail for construction of wooden columns on cement base..
See page 188.
Fig. 151. - Detail for construction of rafters on wooden columns..
See note above is not necessary that the cap be all one piece; when constructed of two or more pieces the joints should be pointed.
Fig. 153. - Detail for construction of rafters on brick piers. Note the stone cap. See also page 191.
It is essential to build anchor bolts in the top of the columns (Fig. 152) to secure the lintels. These bolts should have a four-inch flat iron plate on the bottom to prevent the bolt from being pulled out of place when tightening the nut at the top.
Piers or columns constructed of brick should be of the dark shades; Harvard, Sayre and Fisher, or tapestry brick, are all suitable kinds. They may be laid up with either a broad mortar joint or reveal joints, raking out the mortar for a depth of two to three inches. Brick piers are improved by having a base and cap (Fig. 153) either of cut stone or of brick laid on end with a quarter-inch projection at the bottom and edgewise, set flush with the sides of the piers at the top.
There are times when light brick must be used to conform with the house; but light bricks are anemic looking for pergolas and should be used only when unavoidable.
Stucco columns (Fig. 154) may be built on tile, as it is substantial and economical. Stucco piers should be built on a foundation of stone or concrete projecting beyond the line of the tile. Twelve-inch tile is about the minimum size to use, as it is difficult to hold a smaller size plumb when building.