For the usual front-hole type of box use a plank about 150mm wide and 15mm thick: see the diagram, which shows the sizes of each section to be cut. A strip of leather or rubber makes and ideal hinge for the lid, which should then be fastened down with a catch or clasp. When constructing the box, use screws instead of nails if you can. Wood preservative applied each autumn will prolong the life of the box.
By altering the size of the entrance hole you cut you can determine which species will be most likely to use the box. The following is a guideline to which size holes certain species generally prefer (hole size given in mm): Blue Tit & Coal Tit (25mm), Great Tit & Tree Sparrow (28mm), House Sparrow (32mm), Starling (45mm).
Building a Nestbox
Courtesy of Birdwatch Ireland
Courtesy of Birdwatch Ireland
Make the same box with the upper half of the front taken away altogether for Robins, Pied Wagtails and Wrens. Spotted Flycatchers prefer a somewhat shallower open-fronted box.
Some other species will use specifically designed nestboxes or platforms, including Swift, Swallow, Dipper, Grey Wagtail, Kestrel, Barn Owl, Jackdaw and Treecreeper; for further details of how to construct boxes suitable for these birds please contact BirdWatch Ireland.
Source Garden Bird Detectives Exhibition courtesy of BirdWatch Ireland