http://purplemartin.org/main/mgt.html[/url]":2zn47ksy]I
Houses and gourds should be painted white, or a light pastel color; trim can be any color. White housing seems to attract martins best. White housing reflects the heat of the sun, keeping nestlings cooler. Compartment floor dimensions should measure at least 6"x6," but 7" x 12" offers better protection against predators and weather, if starlings are controlled. Compartment height can be from 5" to 7" high. Place entrance holes about 1" above the floor. Hole size can range from 1-3/4" up to 2-1/4", but 2-1/8" is recommended. Many published plans for martin housing (and some manufactured houses) are made to improper dimensions. If your housing is unsuccessful, check the dimensions and modify where needed.