Anyone looking at how to build a purple martin house should know that most published purple martin house plans were drawn for a bird that nobody had measured yet. The Purple Martin Conservation Association (PMCA) warns in its landlord hints that many published plans and some manufactured houses are built to improper dimensions, and a plan that is wrong at the drawing stage stays wrong in cedar. A DIY purple martin house is realistic for a hobbyist, because the figures that decide the outcome are few and can be checked with a tape measure before any wood is cut.
Martin house plans start with the room a brood needs
The adult is the starting point. The PMCA’s housing page gives a length of 7.5 inches, and an older PMCA standards sheet says 8 inches; either way, a room must hold both parents and four to six nearly grown young, according to the standards. From that the PMCA sets its floor at 6 by 6 inches per compartment and states that rooms measuring 7 by 12 inches from front to back protect nestlings better from predators and weather.
The size of the gain is easy to see on paper. A 6 by 6 inch room has 36 square inches of floor and a 6 by 12 inch room has 72, double. The Missouri Department of Conservation reports that martins prefer the deeper, larger compartments and usually place their nests toward the back, and that larger rooms and nest chambers farther from the entrance generally mean larger clutches and better protection from weather and from owls. It also says the 6 by 6 room is the one that fledges the fewest young, three to four being the norm, and suggests that owners of older houses enlarge rooms to 6 by 12 inches.
Martin house plans can therefore be graded in one line. If the interior is 6 by 6, it is the old design. If it is 6 by 12 or 7 by 12, it follows the current guidance. Check whether the plan lists inside or outside dimensions, because 3/4 inch walls take a share of every board.
Dimension sheet
The purple martin house sizes below come from the PMCA’s standards and hints, each row tied to its source.
| Part | Figure | Source |
|---|---|---|
| Room, minimum | 6 x 6 in | PMCA standards |
| Room, preferred | 7 x 12 in front to back | PMCA standards |
| Crescent entrance | 3 in wide, 1 3/16 in tall | PMCA standards |
| Crescent height above floor | flush, or 1/4 to 1/2 in at most | PMCA hints |
| Round entrance | 2 1/8 in (1 3/4 to 2 1/4 acceptable) | PMCA standards |
| Round entrance above floor | 1 to 1 1/2 in | PMCA standards |
| Board thickness | 3/4 in, untreated | PMCA standards |
| Exterior | white | PMCA standards |
| Interior (wood) | unpainted | PMCA standards |
| Pole height | 12 to 18 ft | PMCA housing page |
| Pole depth | 18 to 25 in in concrete | PMCA standards |
The entrance row carries the most weight. The Missouri department states that a crescent shorter than 1 3/16 inches (1.1875 inches in decimal) keeps martins out, and any fraction taller starts to let starlings in. The PMCA’s instructions are to cut a 3 inch circle template, saw slightly small with a jigsaw and then file or sand to the exact height. Sized right, martins may need a day or so to learn to enter, and some take longer, so a house is judged after a week of traffic, not on the first day.
DIY layout: doors, porches and ventilation
Access is the feature old martin house plans leave out, and a DIY build can add it for the cost of a few hinges. The PMCA says houses without hinged doors, access caps or similar means of opening each room should be avoided, since nest checks, sparrow nest removal and the end-of-season cleaning all depend on it. The T-14 plan answers that with access doors and slide-out nest trays.
The Missouri department adds two layout points. Continuous porches let a single dominant male claim a whole floor, so houses with units spaced around the perimeter often reach greater occupancy, and on a traditional side-by-side house porch dividers can be added. For metal and plastic houses it advises texture on the floor so nestlings can keep their footing, such as silicon shelf liner; wood floors do not cause the splayed-leg problem, it says, though any sub-floor material should drain well and not hold moisture.
Weather is the last item. The PMCA’s standards ask for ventilation holes drilled at an upward angle or placed under the roof overhang so water cannot funnel in, drain holes in each compartment floor so wet nests dry quickly, a roof overhang extended to shed rain, and door plugs to keep other birds out in the off season. Nestlings under 10 days are unfeathered and prone to hypothermia in a rain-soaked nest, which is the reason for the drainage. The Missouri department also suggests foam board in the attic to hold temperatures down.
A wooden house, its weight and a pole that comes down
A wooden house is heavy, and weight dictates the pole. Anyone working out how to build a purple martin house in wood should settle the pole first. The Missouri department puts the dividing line at about 25 pounds: a six or eight compartment house under that can ride a telescoping pole, and anything bigger wants a winch. The T-14, with 14 rooms, is a winch house by the PMCA’s own description. A plan that does not say what the finished house weighs leaves the most expensive decision, the pole, to guesswork.
Material choices are short. The PMCA wants untreated wood in 3/4 inch stock; the Missouri department ranks cypress and cedar highest for longevity, accepts pine and redwood, and says exterior plywood does not last as long as solid boards. Pressure-treated lumber belongs on the mounting post only.
Whatever the pole, the house must come down. Both the PMCA and the Missouri department require raising and lowering on a telescoping pole, pulley or winch, since nests may need clearing daily in a bad sparrow year. The department advises orientation marks on the house so every compartment returns to the same compass direction, because martins that find the house turned can become disoriented and abandon their nests. The pole guard page covers the predator hardware, and the PMCA’s standards add an external owl guard of 2 by 4 inch hardware cloth, removable for nest checks, as a part of any plan.
Purple martin house sizes and where the plan ends
A plan describes the box; the yard decides whether martins use it. NestWatch rates a martin house as a complex build, lists mounting at 10 to 15 feet and says no trees or buildings should stand within 60 feet in any direction. The PMCA puts the minimum at 40 feet and prefers 60. Those placement rules, the choice between a house and a gourd rack and the question of when to open the rooms are covered in the purple martin house guide and on the housing page. Readers who would rather grow their rooms than frame them can start from the gourd drying page, and other cavity designs are collected in the bird house section.
Anyone following a DIY purple martin house route should treat the sizes in the table as the checklist. NestWatch’s own plan sits behind a newsletter sign-up and the PMCA’s T-14 blueprints are copyrighted, so the sources used here give no full cut list. A hobbyist drawing a house from scratch can hold any draft to the purple martin house sizes above: room floor, entrance height and diameter, and the mounting rules.
- Purple Martin Conservation Association: Standards for Purple Martin Housing (PDF)
- Purple Martin Conservation Association: Housing
- Purple Martin Conservation Association: Helpful Hints for Martin Landlords (PDF)
- Missouri Department of Conservation: Missouri's Purple Martins (PDF)
- Cornell Lab NestWatch: Purple Martin nest box
Common questions
What size should the rooms in a purple martin house be?
The Purple Martin Conservation Association (PMCA) sets 6 by 6 inches as the minimum and says rooms 7 by 12 inches front to back protect better against predators and weather and keep nestlings more comfortable. The room has to hold both parents and four to six nearly grown young. Its FAQ asks for cavities of about 6 by 11 inches, so a plan that lands between those figures matches the guidance.
Where can I get purple martin house plans?
The PMCA publishes a 44-page plan booklet for its T-14 house, which has 14 extra-large compartments, access doors and slide-out nest trays and winches up and down. The Missouri Department of Conservation calls the T-14 a traditional Amish design and says detailed, copyrighted blueprints are available from the PMCA. Cornell Lab NestWatch also offers a downloadable plan through its newsletter.
What wood is best for a purple martin house?
The Missouri Department of Conservation says cypress or cedar last longest, with pine or redwood also usable, and that exterior plywood will not last as long as solid stock. The PMCA's standards call for untreated material only, in 3/4 inch stock for better insulation against heat and cold. Pressure-treated wood is acceptable only for mounting posts.
Should a purple martin house be painted?
The outside, yes, in white. White reflects heat and keeps the compartments cooler, according to the PMCA. The inside of a wooden house stays unpainted. The Missouri Department of Conservation gives the same two rules and warns that overheated nestlings will jump out of the house and die.
How heavy can a martin house be on a telescoping pole?
The Missouri Department of Conservation says smaller wooden houses with six or eight compartments weighing 25 pounds or less may go on a telescoping pole. Heavier wooden houses are best raised and lowered with a winch. A tilt-down pole on a hinge is not recommended, because it cannot be used once martins are nesting.
Do the compartments need doors?
Yes. The PMCA's standards say access to each compartment during the nesting season is essential for monitoring, for removing sparrow and starling nests and for cleaning at season's end, and that houses without hinged doors or access caps should be avoided. The Missouri department notes that some designs now have removable nest trays.
How many rooms should a martin house have?
At least four to start, according to the PMCA, which describes six to twelve as a good colony size and says six are more attractive than four. Houses in the Pacific Northwest are the exception, since martins there use gourds and single boxes and do not nest in multiple-room houses.
Should a martin house have a porch?
The Missouri Department of Conservation says better designs eliminate continuous porches, which can let one dominant male take over a whole floor and let nestlings wander out and get lost. Houses with rooms spaced around the edge often reach greater occupancy, and divider boards can be added to a traditional side-by-side house.