Most garden structures are designed to aid the homeowner in caring for plants and flowers; for storing garden tools and sup-plies; as a shelter against the sun, wind, or rain as an enter-tainment center; or simply as a place to relax. Whatever the purpose, the discussion below presents some basic methods of building garden structures, and is a guide from the first plan-ning stages through actual construction.
CHECK LOCAL BUILDING CODES
In most communities, you must obtain a building inspector’s approval of plans for any kind of outdoor structure. Before start-ing the job, it’s wise to check on setback and height restrictions. Once the plans are finalized, they should be submitted to your local building department for approval. A simple plan sketch showing relationship to property lines, lumber dimensions, framing details, and piers and foundations is normally all that is required.
DESIGNING THE STRUCTURE
The use of any garden structure normally determines its design and location. First planning stages must include decisions as to the need for sun and wind control, plumbing and electricity, and storage. Consideration should also be given to the relation of the structure to other activity areas, buildings, and natural objects which take up space in the garden.
Most outdoor structures, like houses, are essentially rectan-gular in plan. Many variations are possible involving the same basic construction elements. If you desire a more intricate design, it is wise to seek professional assistance.
The minimum height of any structure should be eight feet, if possible. No matter what type of roof you select, it should be high enough to allow for head clearance in all areas.
Basic roof designs. The flat and shed roof designs are by far the most commonly used for outdoor structures. The gable and pyramid roofs are somewhat more complicated for the do-it-yourselfer to undertake, but they are basic roof designs and most building contractors can handle them with ease.
Although appearance is often the deciding factor in the design of the roof, if the roof is to be watertight, it should be slightly sloped to allow for moisture run-off.
STRUCTURAL ELEMENTS ARE BASIC
Most garden structures are of post and beam design. Posts, properly spaced to provide adequate support, are set in the ground or securely connected to a firm foundation. The posts support horizontal beams which in turn support the roof rafters at right angles to the beams. Some structures can be attached to existing buildings and a modification of the basic post and beam construction is then used.
SETTING POSTS FOR SUPPORT
For most garden structures, 4 by 4 heartwood posts are sufficiently large. For large structures, bigger posts are sometimes necessary to support heavier roof loads and still maintain wide post spacing.
Posts in the ground. The simplest method of anchoring a supporting post is to set it directly in the ground and firmly tamp the earth around the post until it has sufficient rigidity . If soil is sandy or unstable, a concrete collar should be poured around the post on top of the tamped earth.
The depth to which posts should be set depends on the soil conditions and wind load. 36 inches is adequate for most 8 to 10-foot-high structures.
If you use heartwood posts of redwood, cedar, and other decay-resistant woods, no preservative treatment is usually required before setting the posts directly in the ground but it’s helpful.
When supporting posts are set in the ground, the floor of the structure may be a deck, gravel, paving blocks, grass, or earth. Ordinarily, if a concrete slab is to be poured for the floor, the posts are anchored to the slab rather than set in the ground.
Posts on concrete. Three common methods are illustrated in the sketches below. Patented post anchors of many types, available at most local building supply dealers, may be imbedded in the concrete . This method provides positive anchorage of the posts to the concrete. The nailing block method allows the post to be toenailed to a redwood block that has been set in concrete.
When a concealed anchorage is desired, the drift pin is often used. A moisture barrier-a piece of flat metal or heavy asphalt paper-should be left between the bottom of the post and the concrete surface to avoid the accumulation of moisture and dirt.
If the structure is to be built above an existing deck, the posts may be placed over the existing support members of the deck. The posts should be firmly anchored with angle fasteners .
Beams to posts. When the beam is smaller than the width of the post, it may be bolted to a notched post singly , or in pairs to an unnotched post . If you want to form a column using a pair of posts separated by a spacer block , you can bolt the horizontal member (same width as the spacer block) between the two parts of the column.
HOW TO INSTALL THE RAFTERS
Rafters are normally used to support the finished roof but also may be used alone without other elements to create a roof pattern. The method of installing rafters varies with the manner in which they meet the beam. The most widely used method is to have the rafters resting on top of the supporting member and toenailed in place. If you want to use this method but desire a slightly lower roof height, notch the rafters before toenailing them in place.
Rafters for either a flat or sloping roof which are to be flush with the top of the beam may be attached in one of several ways: a metal rafter hanger; a wood ledger strip nailed under the rafter for support; or the rafter can be toenailed or nailed from the reverse side of the beam.
CONNECTING POSTS AND BEAMS
The basic function of roof beams in any structure is to support the rafters and to tie the posts together, producing solid rigidity. To perform these functions properly, the beams must be adequately connected to the posts. Where design permits, the best bearing is achieved when the beam is placed directly on top of the post.
Several methods of connection are possible. A patented post cap is useful where the beam is the same width as the post. Many of these models are commercially available. A wood cleat can also be used in connecting.
When rafters extend from an existing building, they may be attached either flush or on top of a ledger strip fastened to the building. It is important that the ledger strip be bolted, lag-screwed, or otherwise securely fastened to the existing structure if it is to give the necessary support to the rafters.