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The Complete Book of Birdhouse Construction for Woodworkers
By Scott D. Campbell
Dover Publications, Inc.Copyright © 1984 Scott D. Campbell
All rights reserved.
Wood is the best material for birdhouse construction, for a number of reasons. First, it is easily worked. You can cut, drill, and shape wood in a variety of ways. Second, it is a good insulator against temperature changes and noise. Third, it is widely available in a number of price ranges and in some cases may cost nothing (more on this later). Finally, properly constructed wood birdhouses are durable and can take a variety of different finishes in order to blend with their surroundings.
Wood is available for purchase at lumber and building-supply dealers, conveniently listed in the yellow pages of your phone book under "Lumber." You may purchase stock or standard sizes of plywood or lumber, or if the company offers millwork you can have wood cut to your specifications for an additional price. Generally, those companies which advertise to the home handyman or do-it-yourselfer will give better service, but few offer millwork.
What type of wood should you buy? That depends of course on what woods are in stock and also on what characteristics and price range you desire. A durable wood such as cypress, cedar, or redwood will weather very well but is expensive, and cypress is especially hard to nail. A properly treated pine or fir birdhouse will last for years and is easy to construct. Yellow pine may have some pitch or resin pockets in some pieces, which will have to be cleaned and sealed before finishing. White pine is good and the grain is much less noticeable than in yellow pine. Plywood is both strong and convenient for laying out and cutting designs from, but be sure it is graded as "exterior" plywood, which means that waterproof glues were used to construct it. All cut edges of plywood should be sealed against moisture absorption.
What size lumber should be bought? Lumber should be bought in stock sizes to avoid additional millwork costs if possible. Wood thicknesses can be ¼", 3/8", ½", or ¾", as you prefer, though ¼" and 3/8" lumber are more readily available from craft suppliers. Unfortunately, lumber is sold according to its thickness and width before seasoning and surfacing. Thus a board sold as 1" x 2" is actually about ¾" thick by 1½" wide (see Table 1). From the table you can see that to obtain boards at least ¾" thick and 5" wide, you must glue or nail one-by-threes together or buy one-by-sixes and trim if needed. Be sure to inquire about the actual size of the lumber you are buying if it will affect your plans. Stock lumber lengths are in feet: eight, ten, twelve, and greater lengths. Plywood dimensions are exactly as stated. Plywood is available in 4' x 8' panels and some stores offer it in smaller stock sizes, such as 2' x 4' or 2' x 2'.
Lumber and plywood are also "graded" according to appearance (the smoothness of the surface and the number of knots or waste). Plywood has a letter designation for the quality of its surfaces. For instance, A/C plywood has a superior, smooth surface, designated "A," and a somewhat rougher side, noted as a "C" side. The "A" side will naturally accept a finish better with less effort, and so should face out when the birdhouse is made. Your lumber dealer can help you select the grade of plywood or lumber you need. It is largely a matter of your own preference and the types in stock at the time of your purchase.
What about free wood? Some of the most natural and beautiful birdhouses are made from wood that costs little or nothing at all. Five-inch or larger-diameter logs can be bored or chiseled out to make handsome, sturdy houses. These logs can be found where storms down trees, where trees are cleared for construction, and as driftwood at lake shores. Old packing crates and broken pallets (wooden shipping platforms) are sometimes available at local warehouses. Sturdy, though cheaper and sometimes rough-cut, lumber is used to protect many items that are too expensive or too heavy to be safely shipped in cartons alone. After you have checked the price of lumber at lumber companies you may feel it worthwhile to check with the shipping and receiving departments of larger businesses in your area. A warehouse in this author's area has regularly transported truckloads of damaged pallets to the city dump because the labor and material costs to repair them are not practical.
There is one final type of wood available: rough-sawn wood. Normally wood is cut and then planed to give it a level, smooth surface. Rough-sawn wood, as the name implies, is left in a rough condition for a rustic appearance. Commercial birdhouse builders often groove or otherwise "antique" the wood for that natural or weathered look. Rough wood surfaces are undoubtedly easier also for birds when climbing out of deep birdhouses. This method is most effective with woods like cedar, which age well without painting. Ask your lumberman about obtaining rough-sawn lumber.
Of course wood is not the only material that may be used. Novelty houses have been made from coconut shells, gourds, flowerpots, and various other items, including cement-coated wire mesh. The emphasis in this book, however, will be on the wooden birdhouse.
Tools of the Trade
A brace and bit or small electric drill is required for making entrance, ventilation, and drainage holes. Use ¼" drill bits for ventilation and 1/8" bits for drainage holes if they are required by your design. The most common bit sizes for entrance holes are 1", 1 1/8", 1 ¼", and 1 ½". An adjustable hole saw for use with an electric drill will also cut many larger-size holes.
The lumber may be cut to size with a handsaw. A keyhole saw or a coping saw is used to cut the big-diameter entrance holes for larger birds. The short and sturdy back saw is helpful in making miter and bevel cuts. If power tools are available, the saber saw or the jig saw, which are adjustable for bevel cuts, will perform all the sawing operations needed, except cutting logs.
The only remaining tools required are a hammer, a standard screwdriver, a ruler, a square for straight lines, and wood chisels and gouges (for working with logs).
Designing the Roof
There are three requirements for a roof: (1) the roof should shed water efficiently to prevent it from draining into the nest box, (2) all exposed joints should be sealed tightly, and (3) the roof overhang should keep blowing rain out of the entrance hole.
Requirement (1) involves sealing the roof surface against water penetration and designing the slope of the roof to direct water where it should go. Requirement (2) involves cutting joints to fit well, and proper sealing of all exposed edges. The amount of overhang in requirement (3) is dependent on how near the roof the entrance hole is and how protected the location is where the house will be placed. Some designers use a two-inch overhang minimum as a rule of thumb.
The simplest roof design is the one-piece (Figure 1). The advantage of this design is that there are no joints to leak and the need for those saw cuts can be eliminated.
The simplest two-piece roof uses a butt joint. One edge is placed at a right angle to the other roof-piece edge. For balance, the board on the low or bottom side of the joint should be shorter than the remaining board by a distance equal to the thickness of the boards used. Interesting effects can be achieved by making one piece much larger than another—particularly if the roof goes from front to back rather than from side to side of the house (Fig. 2).
A variation of the butt joint is the lap joint. A recess is cut into the edge of one board, which allows the edge of the joining piece to fit into it. This design exposes less end grain of the wood and provides more surface area for gluing (Fig. 3).
The most exacting and therefore the most challenging two-piece roof involves beveling or cutting mating roof edges to meet exactly at the middle of the high point of the house and thus match the degree of slope of the roof.
The greater the cutting angle used for a bevel cut, the more sharply the roof will slope. Unfortunately, it is nearly impossible to get a perfect bevel joint without using calibrated power tools. One method, which requires patience and care, can produce satisfactory results with a minimum of sanding or touch up. Start by acquiring a guide block (made from any scrap of lumber that is several inches wide and thick, such as a two by four) and have it cut to the desired angle at a cabinet shop or lumberyard. Temporarily nail or securely clamp this block to the board to be cut. Lay a saw (preferably a back saw for better control) against the angle cut in the guide block and very slowly cut into the wood beneath the guide. If the saw is kept flat against the guide it will duplicate the guide angle in the wood below (Fig. 4).
Remember that when you cut a bevel in the middle of a board you will have two equal pieces of wood with the same angle. One piece will slope from top to bottom while the edge of the opposite piece slopes from bottom to top. Just turn one piece over and rejoin the boards to form the roof.
At roof peaks, where joints in the wood may leak if not protected, roofs are often overlaid with a strip of tin or aluminum or with roll roofing. A roof made entirely of metal or of asphalt shingles or roll roofing is not advisable, as heat buildup will occur unless the birdhouse is placed in a sheltered, shady area. Adequate ventilation or an insulating wood layer beneath the outer roof shell can also counteract some of the heat. If the heat-accumulating properties of a design are in question, they can be checked by placing a thermometer in the birdhouse. To find scrap roofing material, check construction sites and roofing contractors.
See Fig. 5 for some design suggestions for multisection roofs.
All types of houses should have a detachable or hinged roof, floor, or side that will allow the house to be cleaned of accumulated debris. This feature reduces the chance of a disease or parasite being transmitted from one breeding season to the next and prepares the house for the new occupant next spring.
One method uses a hinged roof or floor. Hinges may be actual hinge hardware, or devised from a flexible piece of leather, rubber, or tough fabric. Naturally, nonmetallic materials should only be used for roofs, or for sides where the weight of the bird will not be against the hinge, which might fail under stress. Brass screws can be used to secure the cleanout when not in use.
Cleanouts can also pivot on a nail or bar. For this kind of cleanout, choose a side or floor that is between two opposing sides of the house. Drill directly opposite holes, slightly smaller than the diameter of the nails to be used, through the opposing sides of the house and into the cleanout to the depth of the nails' lengths. Remove the cleanout and redrill the two opposing holes in the cleanout to the diameter of the nails used. When the house is nailed together the heads of the nails will have a tendency to be held tight in the smaller-diameter holes of the opposing sides, but the part of the nails that extends into the larger holes in the cleanout will allow the cleanout to pivot freely on the nails.
The open-back method involves screwing a birdhouse made without a back to a mounting board which serves as the back. To clean, unscrew the house and leave the mounting board in place. The board may be a smooth wall of a garage under the protecting eave of the garage roof. The outer edge of the birdhouse should be caulked to prevent rain leaks. The backing board should be painted to match or blend with the wall it is attached to.
The sliding-drawer method involves cutting grooves or rabbets in three sides of the bottom of the inside of the house. The fourth side is slotted to allow a floor panel to be pushed in or pulled out. A drawer pull can be attached to the edge and a locking screw can be used on one or more sides to keep the drawer closed when not in use.
To avoid using rabbets, pieces of quarter round or other wood molding or strips of wood can be placed under the drawer to support it and allow it to slide in and out. The drawer itself can be a simple board or a true drawer with front, back, and sides.
Cleanouts can also employ pins, pegs, hooks, catches, movable or stationary cleats, and screws (see Fig. 6).
Drainage and Ventilation
Drainage holes in the bottom of the house may be necessary to keep water from collecting inside during a heavy or extended rainstorm. This problem is most likely to occur if the eaves do not extend far enough beyond the entrance hole to keep out blowing rain or if the roof should develop a leak. A few 1/8" holes in the bottom of the house floor should be sufficient.
Ventilation holes are sometimes also made necessary by the design of the house. If the interior of the house is small and the entrance opening is near the roof, the opening should provide adequate ventilation. If, however, the house is a large one with plenty of surface area exposed to the sun or if the entrance hole is well below the peak so that heat can build up near the top of the house, then ventilation holes are advisable. Simply drill two or three ¼" holes above the entrance and near the peak of the roof. Some designers shorten the left and right sides of the house by ¼" so that they don't quite reach the roof and thus allow side-to-side ventilation.
The size and shape of the entrance hole is a very critical part of the design. If the hole is too large it either will not attract the bird you wish or may allow predators to get in and rob the nest. Larger and undesired species of birds may appropriate the birdhouse for their own. An example of careful design is the unconventional, elliptical entrance of the wood-duck house or nest box, which is designed to let wood ducks in but keep raccoons out. See Chapter III for detailed design specifications.
If entrance perches are desired, ¼" hardwood dowels can be purchased at hardware stores. The value of these perches to nesting birds is debatable, but they can enhance the appearance of some designs if this is important to the builder.
Natural cavities used by birds for nesting have rough-surfaced interiors with plenty of footholds for birds—especially useful to young, inexperienced nestlings exiting the nest. If a birdhouse is both deep and made of smooth, finished lumber, footholds become more important. Hardware cloth, cleats, a narrow incline, or wood dowels glued flat against the surface can artificially roughen the wood for footholds. A series of horizontal grooves cut into the wood below the entrance can help achieve the same purpose.
Construction Tips and Techniques
There are a number of techniques and short cuts that can make birdhouse construction work quicker to complete, longer-lasting, or more beautiful.
First, since most birdhouse designs are simple box shapes, at least two of the sides are usually of the same dimensions. It is therefore possible to clamp or brad two pieces of wood together and make the same cuts on each at the same time.
Secondly, if you use waterproof glue to fasten joints along with nails, the nails will hold the pieces fast until the glue dries. After the glue has dried, the joints not only are stronger but are sealed better against the rain.
Remember that, when working with woods that split easily, you should predrill nail holes a few sizes smaller than the nails to be used. This is also advisable if softer, nonrusting aluminum nails are used in heavy or dense woods. Aluminum nails are available at hardware stores, building-supply stores, and wherever aluminum-siding products are sold. Brass screws can also be used, will not rust, and are a common hardware-store item.
Some types of bits and woods tend to cause splintering when entrance holes are bored through. For this reason bore from the front side of the entrance through to the interior side and place a block of scrap wood under the exit point area to prevent splinters from forming when the bit exits the wood.
When natural log houses are desired, carefully split or saw the log down the middle of its length. The logs should be thoroughly air-dried beforehand. The inside of the log is then hollowed out using wood chisels or gouges. A series of overlapping holes can also be drilled, but this is time-consuming with hand tools and hard on the bits in heartwood.
Also remember that even plywood that looks smooth will require some light sanding with medium- and fine-grade sandpaper to form a truly smooth finish. In addition, if the method of finishing used on a birdhouse will allow the grain of the wood to show through, it becomes necessary to "balance" the positioning of the grain of the boards. Balancing involves aligning the direction of the grain of lumber so that boards that appear identical to the eye have their grain patterns running in the same direction. Thus, the roof boards would have their grain patterns running in the same direction, as would the left and right sides and the front and back sides. Any of the three groups could have a different grain position but usually the roof boards have their grain running at right angles to that of the four sides.
Use good exterior-grade paints, stains, or varnishes to protect the exterior of the birdhouse. Use dull browns, greens, and grays that will blend with the surroundings. The natural instinct of birds is to seek inconspicuous hideaways in which to rear their young. The only exception to this rule is the attraction of the purple martin to the relative coolness of white birdhouses (white is cooler because it reflects more light than other colors). Do not use finish on the interior of the house—it seems unnatural to the bird and is unnecessary.
Excerpted from The Complete Book of Birdhouse Construction for Woodworkers by Scott D. Campbell. Copyright © 1984 Scott D. Campbell. Excerpted by permission of Dover Publications, Inc..
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