Build an owl box

Find out why indoor Barn Owl nestboxes are the best option.

Do you have a suitable building?

Ideal buildings for Barn Owl nestboxes are:

  • At least 4 metres high.
  • With an opening or hole at least 3 metres above ground level which overlooks open countryside.
  • Where the nestbox can be positioned 3+ metres above the ground.
  • Where the nestbox access hole is visible to an owl from the most likely entrance point.
  • Ideally within 1 km of areas or strips of rough grassland.

It’s worth bearing in mind that:

  • It doesn’t matter what the building is made of, or used for, and its position in relation to your house makes no difference.
  • Barn Owls can learn to tolerate noise and activity as long as they have something to hide in – such as a nestbox.
  • When choosing the building and the owl box position, remember that Barn Owls are interested in openings and holes rather than buildings or boxes. The way in needs to be visible. See our photo gallery suitable positions for Barn Owl nestboxes in buildings.
  • See a photo gallery of openings and holes that are attractive to Barn Owls.

Why we don’t recommend fixing one on the outside of a building

  • Inside the building, the owls will benefit from the additional shelter. Outside they are more exposed.
  • An indoor Barn Owl nestbox is not suitable for outdoor use, and an outdoor nestbox is much better placed in a tree – because trees usually afford more shelter and owlets can sometimes climb a tree to re-enter the box.
  • A box on the outside will only last about 10-15 years. A box on the inside will last as long as the building.
  • Nestboxes designed for indoor use are quicker, cheaper, and easier to build. Or cheaper to buy.

Is your landscape suitable?

Most old barns are good places for nestboxes – without one only 48% have a nesting place.

  • Barn Owl nestboxes in the UK should be placed inside rural buildings that overlook open habitat.
  • Avoid urban, suburban, dense forest and high mountain areas.
  • Sites within 1 km of a motorway or other fast, unscreened, main roads should be avoided due to the risk of road-deaths.
  • Nestboxes do not need to be placed directly on patches or strips of rough grassland as the birds are perfectly capable of ‘commuting’ across unsuitable habitats before starting to hunt and have very large home ranges.
  • Check to see if your local landscape is suitable.

How to build indoor Barn Owl nestboxes:

Modern barns are very often perfect for nestboxes but without one, 97% are unsuitable for Barn Owls.

  • Dimensions.
  • Materials to use.
  • Construction and plans for Barn Owl nestboxes.
  • Where to position a nestbox in a building.
  • How to put up Barn Owl boxes.
  • Human access and cleaning out.
  • Your safety.
  • Nest box criteria for assessing other plans or designs for interior Barn Owl boxes. Poor design can be fatal.

Or you can simply buy a Barn Owl Trust nestbox for inside a building.

Dimensions

The dimensions given on the owl box diagram below are the minimum required size.

An ideal nesting box would be much bigger: a full 1 metre from the bottom of the entrance hole to the bottom of the box and with a floor area of at least 1 metre x 1 metre. However, owl boxes that big would be very difficult to erect and more expensive to build.

Materials to use

The basic box should be built using 9mm FSC approved plywood and 50 x 25mm batten. Softwood ply (usually Scandinavian or Canadian) is perfectly adequate, cheaper, and better for the environment than hardwood. We use 30, 40 and 50mm screws but nailing and/or gluing is perfectly acceptable.

How to build a Barn Owl nestbox

Watch the video at the top of this page or have a look at our photo guide – How to build an indoor Barn Owl nestbox.

  • Our deep nestbox design is very safe for owlets due to a 450mm drop from the entrance hole to the bottom and an exercise platform with a raised edge.
  • If you wish to vary from this owl box diagram, please check our essential criteria for interior Barn Owl boxes.

How to erect a Barn Owl nestbox in a building

Watch the video below or have a look at our Photoguide: How to put up an indoor nest box for Barn Owls – showing the 5 possible methods to use when erecting indoor Barn Owl nestboxes. Each method is suitable for different types of barn or farm building, depending on the construction.

Human access and cleaning out

  • Maintaining the internal depth of the nesting box reduces the chances of a nestling Barn Owl falling from the box and dying as a result of neglect or predation. Therefore it’s important to clear it out if there’s more than about 75mm of nest debris.
  • If Jackdaws use the box it must be cleaned out every year (wear gloves and a dust mask).
  • Boxes only used by Barn Owls and/or doves will need clearing out every 2 or 3 years at most (unless the owls have very large broods of young or breed more than once a year in which case they should be cleaned out every 1 or 2 years).
  • It’s usually best to clean out nestboxes between November and January so as not to disturb breeding Barn Owls (which is illegal – see Barn Owls and the law).
  • If owls are roosting in the box, it’s best to wait until the weather is dry with little wind, to avoid flushing them out into bad weather. (Barn Owls’ feathers are not waterproof and they can get waterlogged and chilled in wind and rain.)

The most important thing when erecting the box is your own safety!

Your safety

  • Before erecting a box, please ensure that you have properly assessed the risks involved, particularly with regard to working at height.
  • A nestbox is quite heavy to lift single-handed and using ladders is potentially dangerous.
  • Please do not work alone and consider using two ladders or safer methods.

Below are the essential requirements for Barn Owl nest box plans:

What is a good nestbox design? – List of criteria for indoor Barn Owl boxes

  • Entrance hole: Optimum size 130 x 130mm; minimum 100 x 100mm; maximum 150 x 150mm.
  • Floor area* of nest chamber: Good size range 0.2 to 0.4 m2. Absolute minimum 0.16m2.
    The floor of the box featured on this page measures 500 x 400mm giving a floor area of 0.2m2.
  • Depth* from bottom of entrance hole to nest floor must be not less than 450mm.
    • *Note: The ideal floor area size is 1m2 x 1m deep but such big boxes are generally impractical.
  • For American Barn Owls all the minimum dimensions except the entrance hole should be increased by 50%.
  • For any Barn Owl nestbox less than 700mm deep, an exercise/landing platform below the entrance hole is vital for the safety of young fledglings. Climbing/jumping young birds can get from the platform onto the roof of the box and (ideally) onto other nearby perching places.
    • The platform must have a generous raised edge suitable for Barn Owls to grip easily.
  • Human access for easy clearing-out of nest debris is essential.
  • Measures aimed at reducing the chances of entry by other species (such as Jackdaws) are to be encouraged provided that they do not significantly reduce the box’s suitability for Barn Owls. In mainland Europe, measures to exclude Beech Martens are an important consideration.
  • Weight: Should be substantially constructed yet light enough to permit safe erection using basic equipment. Normal indoor-box weight range is 10-15 kg. Total weight for erection by hand should not exceed 18 kg and an indoor-box under 8 kg is probably not substantial enough.
  • Materials: Should not be constructed from tropical hardwood unless the timber is certified as sustainably grown.
  • Essential information:
    Information supplied with this type of nestbox should specify:
    • Height of at least 3m above ground level.
    • Position where the box will be completely dry for many years.
    • How to maximise the chances of occupation (entrance hole visibility for birds flying into the building and building entrance visibility to birds flying outside).
    • The need for clearing out debris so as to maintain internal depth.
    • Box erection and attachment methods, human safety issues.
    • Landscape requirements.
    • Barn Owl nestboxes should generally not be within 1 km of any motorway, dual-carriageway or similar unscreened major road.
  • Avoid poor nestbox design – which can kill owlets.
  • Clearing out nest spaces

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Great Horned Owl at Nest Box – Human Made Nests Are Helping Birds

Great Horned Owl nest box – Nikon D500, f7.1, 1/125, ISO 500, -0.7 EV, Nikkor 500mm VR with 1.4x TC, natural light

There are a couple of owl nest boxes at the hay barn on Antelope Island State Park and over the years I have seen both Barn and Great Horned Owls use those nest boxes to rear their young. The nest boxes aren’t pretty and that is because they don’t need to be and some people feel that the unnatural setting isn’t ideal for bird photography because of that. I know I have felt that way in the past but I’m changing my thoughts on that because…

Those unappealing nest boxes are helpful for the owls, they provide a safe place to lay their eggs, incubate them and to rear their young to fledging. Human made nest boxes, nest baskets, birdhouses, nest shelves and nest platforms can and do help many species of birds in all types of habitats.

When I lived in Virginia I had a metal shed at the back of my garden and one of the doors to the shed never closed tightly, one day I went out into the shed and found a Carolina Wren nesting in my motorcycle helmet, it kind of ruined the helmet but I enjoyed knowing the wren was using the helmet to rise her chicks. After that nesting season I went out and purchased an unglazed terracotta bird nest “jar” (sometimes called a bottle) and installed it below the flower box at my kitchen window and for years and years the Carolina Wrens used it to raise their young.

I couldn’t see the nest from the kitchen but it always made me feel good that I had provided them with a safe place for them to raise their young. I also had bluebird boxes and wooden nest boxes that a variety of birds & flying squirrels used. I lived way out in the country in Virginia and really enjoyed watching all the birds that came to my yard. I wasn’t a bird photographer at the time but now I wish I had been back then.

I left snags standing in my yard and garden for the woodpeckers and they excavated cavities that other birds would use, woodpeckers are primary cavity nesters and other birds called secondary cavity nesters use those nests later on. But we humans often pull those old trees down because we don’t like how they look or they present safety issues. I remember feeling awful that I had to use my Jeep Cherokee to pull down a poplar snag one winter because it was eventually going to crash onto my fence, while I pulled that snag down I kept thinking that I was removing a “potential” home for the birds and I felt awful about that. Here it is nearly twenty years later and I still feel bad for taking down that snag.

There are a lot of bird lovers out there though that are providing safe nesting places by constructing nesting platforms, nesting shelves, nest baskets and nest boxes to provide safe nesting locations for owls, ducks, wrens, geese, swallows, bluebirds, flickers, kestrels, wading birds, eagles, ospreys, flycatchers, warblers, chickadees, nuthatches and many other species of birds.

Are they always pretty? No, but as I mentioned above they don’t need to be and the birds don’t care about aesthetics their only need is for a safe place to rear their young.

Life is good.

Mia

NestWatch.org (A nice site that can help people select the best man made nest for location and species)

I know there are many other links I could share but I am running out of time this morning.

  • Food: Owls will not visit bird feeders, but it is possible to provide a steady food source for these hunters. Because owls eat mice, voles, gophers, and similar small rodents, birders who have mice nearby are more likely to attract owls. Leaving grass uncut, adding a brush pile, and leaving seed on the ground will make the yard more mouse-friendly, which in turn makes the habitat more owl-friendly. Avoid using poisons or traps to eliminate mice or other prey, and let owls take care of the problem instead.
  • Water: Owls get the vast majority of the fluid they need in their diets from the prey they consume, and they are not frequent visitors to bird baths. In hotter climates and during the summer, however, owls may visit slightly larger, deeper birdbaths to drink or bathe. Providing this type of water source in a quiet, secluded area is more likely to encourage owls to visit.
  • Shelter: Owls need somewhat dense, mature trees with good trunks to roost during the day, preferably in a shaded, secluded area. Both coniferous and deciduous trees are suitable if they are a good size. Empty owl nest boxes are also good alternatives to natural shelter, but providing natural spaces where the owls can feel safe during the day is the best way to encourage them to roost nearby.
  • Nesting Sites: Hollow trees are most owls’ preferred nesting sites. Smaller owl species that are more likely to be common in yards and gardens may also use large nest boxes that are positioned 10-20 feet above the ground on a large tree. Barn owls may also use abandoned buildings for nesting, and leaving a barn or shed open for the birds to access can give them a great place to raise a brood of owlets. Nest boxes for owls should be put up by January or February since these birds nest much earlier than other backyard species. The boxes should be monitored to be kept free from wasps, squirrels, rodents, raccoons, or other birds or guests that may discourage nesting owls.

Barn owl nest boxes

Exterior barn owl nestboxes can be fixed to trees or to the outside of buildings.

Where possible, they should face onto grassland and be reasonably conspicuous with an open flight path to them. They should not face into the prevailing wind.

Although barn owl nests are usually well spaced out, placing boxes in pairs, from twenty to a few hundred metres apart, will provide a pair with roosting as well as nesting sites. The male and female roost separately, and some pairs use different boxes in those good years when they can have two broods.

Since many barn owls are killed by road traffic, it is best not to put up owl boxes close to motorways and main roads.

Barn owls are specially protected by law, and so it is illegal to disturb them close to their nest. Occupied nests – even your box – should only be visited by someone who holds a licence.

Make an exterior nestbox

As you make up the A-frame box, attach a 200 x 485mm piece of rough-sawn timber to the inside of the back panel. The fixing to the tree will go through this reinforcement. Don’t attach the front panel until the box is hung up.

You can print a plan for an external barn owl nestbox here.

How to Build a Barn Owl Nest

Unlike other owl species, like great-horned owl or barred owl, barn owls have a heavy preference for rats and mice. And while they might be adorable, they are also natural killers. Barn owls hear so well that a mouse’s heartbeat alerts them to nearby prey. Their velvety feathers allow them to approach their victims silently in total darkness, a busy time to hunt. One barn owl can cover over a mile and will eat between three and six mice each night, approximately 2,000 mice yearly. A family, including chicks, in one nest box, can devour 8,000 mice in one year.

One barn owl can cover an area of over a mile and will eat between three and six mice each night, approximately 2,000 mice yearly. A family, including chicks, in one nest box, can devour 8,000 mice in one year.

So how to get owls to take up residence on your property? Barn owls want homes that are cozy, warm and safe. Many live in rafters, tree cavities and in barns because they do not build nests. This gives farmers the opportunity to provide a home and enable owls to hunt rodents in fields, improving crop production, yield and profit.

There are several designs for building nest houses which range from an elaborate two floors along with perches to a simple one-floor box. Each type requires specific measurements a barn owl needs for comfort and family growth.

You will need: plywood, galvanized nails, plastic resin or wood glue, paint, 4 x 4 posts, wire, sawdust or woodchips and a few basic tools.

1. Find Your Location

Because placement of boxes is crucial, the first step is to take a close look at rodent-infested areas and estimate the number of boxes required, figuring one box for every 640 acres. Make sure the box will be safe from any cats, gophers or raccoons by placing it within 100 yards of any large tree that creates an umbrella of protection, such as an oak or sycamore. Because barn owls fly low, make sure the boxes are away from any road traffic and human activity.

2. Find the Right Box for You

Next, decide on the type of nesting box you desire, from elaborate designs complete with indoor-outdoor perches and insulation to simple one-room construction. A one-room nest includes minimum dimensions of 12 inches by 12 inches for the floor and a cavity depth of 16 inches. The entrance should be approximately five to six inches in diameter, located near the floor of the box to provide availability for young chicks. Include a room in the main frame 16 inches by 26 inches to give a one-inch overhang all around.

3. Make the Box

To construct the nesting box, you can use scrap exterior grade three-eighths inch or one-half inch plywood and #4 or #5 galvanized hot dipped nails. When all sections have been cut, use a marine grade plastic resin or exterior wood glue to assemble.

4. Allow for Airflow

Once the frame is completed, drill vent holes to allow air circulation near the roof. Follow with a water drainage plan by making additional holes in the floor, near the corners of the box.

5. Spruce It Up

Two inches of sawdust or woodchips may be placed on the floor. Then, to spruce it up and prevent wood warp, paint the finished boxes a dull green, black or brown color to help camouflage the nest. Use an oil based stain or latex-based paint on the exterior only.

6. Decide If You Want to Build a Neighborhood

When you have completed the house, you can install a single or multiple boxes at the end of your produce rows.

7. Mount Your Box

On a 16-foot-high 4′ x 4′ post buried 3.5 feet in the ground. Once a box is placed on a post, it is best to wrap it with a metal, conical predator guard.

8. Keep Your Box Clean

To reassure return of barn owls and their families, make sure to clean and inspect any box on the premises twice each year, in June and in November. Because birds bring all kinds of vegetation and hair into the box to keep their brood safe and warm, parasites easily enter. Open the box carefully and lift the box down from its’ position, then scoop out all the contents including unhatched eggs. Place all of the contents into a plastic bag and close tightly, disposing away from children and animals. Scrub the inside and outside of the box with boiling water and let it air dry. Lay fresh sawdust on the floor. And keep your distance from the box to allow new barn owl families to discover their home.

Provide decent living quarters and barn owls may help keep your fields free from pesticide usage, free from predators, increase their population and offer quality environmental and sustainable green space for everyone. For further information and references, you can contact the Dept. of Conservation, the Barn Owl Center, the Barn Owl Conservation Network and the Santa Clara Audubon Society.

Go forth and build yourself a barn owl nest box!

Creating Owl Boxes: How To Build An Owl House

If owls live in your area, building and installing an owl box might attract a pair to your backyard. Some common owl species, like barn owls, are ferocious predators of mice and other rodent pests, so it makes sense to invite them into the neighborhood by installing an owl house. Read on for tips on owl house design.

Owl House Design

Your owl box plans do not need to be fancy to be effective, but you’ll need to figure out how to build an owl house that is the right size to be a nest-substitute for the type of owl you hope to attract the garden. Obtain information on the size of the owl species before you begin your owl box plans.

For barn owls, a simple wooden box

about 38 by 18 by 12 inches (1 by .5 by .3 m.) provides adequate room for a pair of owls and their young. For other species, the size will vary. Always use untreated wood such as fir, cedar or pine.

Your owl house design must include an entrance opening located some 6 inches (15 cm.) above the base of the box. For barn owls, this can be a square about 6 by 7 inches (15 by 17 cm.) or an ellipse with a horizontal axis of 4 ½ inches (11.5 cm.) and a vertical axis of 3 ¾ inches (9.5 cm.) depending on your owl house design. Don’t forget to include drain holes in the owl box plans.

It is very important that the owl nest box is built solidly. You don’t want it to fall apart after a family of owls moves into it. Correct owl nest box placement is also essential.

Owl Nest Box Placement

Take the time to install your owl box appropriately. Attach it solidly to a stable post, the rafters of a barn, a tall tree, a barn wall, or any other handy structure. Consider placement when creating owl boxes so that you can include whatever attachments are necessary.

In the ideal owl nest box placement, the box will be located near an open field so that the owls can glide directly into the box from hunting. You should face the entrance hole toward the north to prevent the sun from heating up the box.

Firstly, have you considered putting a Barn Owl box inside a building?

There are lots of reasons why Barn Owl boxes in buildings are better than nestboxes in trees.
They are cheaper too!

However, if you have a suitable tree, tree boxes are much more practical than boxes on poles.

Do you have a suitable tree?

An ideal tree would be:

This ideal tree stands in a patch of good habitat.

  • A mature tree with a thick trunk.
  • Isolated, in a hedgerow or on the woodland edge.
  • With a high canopy.
  • With few or no low branches.
  • Where a nestbox can be placed at least 3 metres above ground level.
  • Where the nestbox access hole would be visible to a passing owl, even when the tree is in full leaf and seen from a distance.
  • Quite close to strips or patches of rough grassland.

Watch the video above or see our Photoguide: Choosing the right tree for a Barn Owl box.

Why we don’t recommend fixing a tree box on a pole

  • On a live tree, owls benefit from additional shelter. On a pole they are far more exposed.
  • A tree box with an internal depth of 450mm reduces the chance of owlets falling (before they are ready to fly) but it does not eliminate the danger entirely. With a well designed tree-mounted box, a fallen owlet might be able to scramble up the tree trunk and re-enter the box. In the case of a tree box mounted on a pole, this is impossible.
  • A well designed pole box is much bigger and much deeper than one designed for fixing to a tree. This eliminates the danger of owlets falling because they cannot get out until they are able to fly.

Top tips for nestbox trees:

  • Barn Owls are interested in holes rather than boxes.
  • Face the access hole towards open ground but avoid the prevailing weather if possible.
  • Trees with low branches/leaves and trees screened by other trees/buildings are not suitable because the access hole will be hidden.
  • Trees within woodland are very unlikely to attract Barn Owls.

A mixed farming landscape with patches and strips of rough grassland is ideal.

  • Barn Owl nest boxes in the UK & Ireland should be placed in open countryside in isolated trees or trees that overlook open habitat.
  • Avoid urban, suburban, dense forest and high mountain areas.
  • Sites within 1 km of a motorway or other fast, unscreened main road should be avoided due to the risk of road-deaths.
  • Nestboxes do not need to be placed within rough grassland as the birds are perfectly capable of ‘commuting’ across unsuitable habitats before starting to hunt and have very large home ranges.
  • Check to see if your local landscape is suitable.

You can build a Barn Owl treebox or you can simply
buy a Barn Owl Trust nestbox for fixing to a tree.

Barn Owl tree nestbox instructions:

  • Dimensions.
  • Materials to use.
    • Preservative.
    • Waterproofing.
  • Barn Owl box plan and construction.
  • How to put up a tree box.
  • How and when to clean it out.
  • Your safety.
  • Essential requirements for Barn Owl tree box designs.

Dimensions

The dimensions given in the owl box plans below must be treated as the minimum required size.

Ideal Barn Owl boxes would be much bigger: a full 1 metre from the bottom of the entrance hole to the bottom of the box and with a floor area of at least 1m x 1m. However, owl boxes that big would be very difficult to erect and more expensive to build.

Materials to use

The basic owl box should be built using rot-resistant or Tanalith E treated sheet material manufactured using a waterproof adhesive. We use 9mm exterior grade tanalised softwood ply (or structural exterior grade ply complying with EN314-2 Class 3, CE2+ or C+/C), 25 x 50mm tanalised batten and 30mm rust-resistant screws. Please avoid using hardwood ply, unless it is stamped “FSC Approved”.

Wood preservative

Where tanalised plywood is not available, any type of wood preservative may be used provided that the box is dry before erection. It is essential that the edges and ends of all parts are treated before assembly.

Waterproofing

The top of the owl box should be covered with heavy duty roofing felt. A waterproof sealant (such as Ever-Build Weather-Mate) should be used in all the wood joints to prevent water seeping in. If you need proof that this is necessary, try leaving your nestbox under a sprinkler for a few hours. 20mm diameter drainage holes can also be drilled in the floor of the box. The front, back and sides must overhang the floor of the box.

Note: The use of external preservative and waterproof sealant in the joints will not stop the plywood de-laminating. You must choose plywood made with a waterproof adhesive (EN314-2, Class 3).

How to build a Barn Owl tree nestbox

Watch the video above or have a look at our photo guide – how to build a Barn Owl Tree Nestbox.

  • Our deep nest box design is much safer for owlets due to a 450mm drop from the entrance hole to the floor and a landing tray with a raised edge.
  • If you wish to vary from this owl box diagram, please check our essential criteria for exterior Barn Owl boxes.

How to erect Barn Owl boxes for trees

Watch the video above or see our photo gallery showing the 2 methods to use when erecting Barn Owl boxes for trees.

Human access and cleaning out

The front of the owl box should have an access panel to enable nest debris to be cleared out periodically. The internal depth of the nest box is important as it reduces the chances of a nestling Barn Owl falling from the box and dying as a result of neglect or predation.
Therefore it is important that the box depth is maintained by clearing out the box once it has more than about 80mm of nest debris. If Jackdaws use the box it must be cleaned out every year (wear gloves and a dust mask). Boxes used only by breeding Barn Owls will need clearing out every 2 or 3 years. Remember that under the Wildlife and Countryside Act 1981, it is an offence to disturb breeding Barn Owls so nestboxes should only be cleaned out between November and January – and preferably in dry, calm weather, so that any roosting owl doesn’t get flushed out into the rain or wind.

Before erecting a Barn Owl box, please ensure that you have properly assessed the risks involved, particularly with regard to working at height. An outdoor box is quite heavy to lift single-handed and using ladders is potentially dangerous. Please do not work alone and consider using 2 ladders with appropriate PPE (Personal Protective Equipment such as fall arrest and ladder anti-slip equipment), or safer methods. The most important thing when erecting the box is your own safety.

Minimum requirements for Barn Owl treebox designs

If you choose to use a different design for your tree nestbox, ensure it meets these criteria:

  • Entrance hole: Optimum size: 100 x 130mm; minimum size: 100 x 100mm; maximum size: 150 x 150mm.
  • Floor area of nest chamber: Good size range: 0.2 to 0.4m2; absolute minimum: 0.16m2.
  • Depth from bottom of entrance hole to nest must be not less than 450mm.
    • NB: owl boxes with less depth may be acceptable if placed within the branches of a tree that a fallen nestling could climb, however, deep owl boxes are so much safer that we no longer recommend boxes with less depth.
    • The ideal size for Barn Owl boxes is 1m2 (floor area) x 1m depth but such big boxes are generally impractical.
  • For any Barn Owl nestbox less than 700mm deep, an exercise/landing platform below the entrance hole is vital for the safety of young fledglings. Climbing/jumping young birds can get from the platform onto the roof of the box and (ideally) onto other nearby perching places.
    • The platform must have a generous raised edge suitable for Barn Owls to grip easily and it should be positioned, and have sufficient shelter and drainage, to prevent rainwater being deflected into the box entrance.
  • Interior must remain dry during prolonged heavy rain coming from any direction.
  • All sides should overhang the floor. Outdoor nestboxes usually have drainage holes. However, any nestbox that actually needs drainage holes (to let rainwater out) is a very poor design and should not be used.
  • There must be sufficient height difference between the nest and the external platform so as to prevent the accumulation of a continuous (internal/external) layer of pellet debris allowing rainwater to soak through the debris to the inside thereby chilling the nest contents.
  • Roof should be covered in thick roofing felt guaranteed for not less than 10 years. Very steeply sloping roofs may not need covering but any apex join must be permanently waterproofed.
  • Human access for easy clearing-out of nest debris is essential.
  • Timber liable to decay within 20 years must be treated with long-lasting preservative: either pressure treated (tanalised) or surface treated including all edges of all component parts before assembly (follow product instructions and make sure all parts are dry before assembly). Plywood used must be manufactured using a waterproof adhesive (EN-314-2, Class 3).
  • All screws/nails and any metal fittings used should be rust proof.
  • Measures aimed at reducing the chances of entry by other species (such as Jackdaws and Beech Martens) are to be encouraged provided that they do not significantly reduce the box’s suitability for Barn Owls.
  • Should be substantially constructed yet light enough to permit safe erection using basic equipment. Normal treebox weight range is 13-18kg. Total weight should not exceed 25kg and a tree box under 10 kg is probably not substantial enough.
  • Should not be constructed from tropical hardwood unless the timber is certified as sustainably grown (FSC approved).
  • Barn Owl boxes should be supplied with information that specifies an erection height of not less than 3m above ground level and stresses the importance of positioning within the tree branches in the case of boxes that have less than 450mm internal drop.
    • Information provided with owl boxes should also cover the following subjects:
      • foraging habitat requirements, nestbox positioning to maximise the chances of occupation (entrance hole visibility), the need for clearing out debris so as to maintain internal depth, nest box erection and attachment methods, human safety issues.
  • As a general rule, Barn Owl boxes should not be erected within 1 km of any motorway, dual-carriageway or similar unscreened major road.
  • Avoid poor nestbox design
  • Clearing out nest spaces

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