Barn Owl Nest Box Guidelines

You don't need detailed plans to build a good barn owl nest box. What you do need is the right key measurements: the size of the entrance hole, the floor area, and the drop from the hole down to the floor. Get those right, build it strong and dry, and put it in the right place, and you've every chance of success.

This is the checklist I use for my own boxes, including the oak barrel boxes you can watch on our live barn owl camera. Our male, Buster, has raised a brood in one every year so far, so I know these sizes work.

📏 The key sizes at a glance

🔍 The measurements explained

🕳️ Entrance hole

The ideal is about 130 x 130mm, with 100mm as the smallest and 150mm as the largest I'd go.

🦉 What I do: I use a 140mm hole saw, and it's perfect: easy for the owls to get in, but not too big. Tawny owls can still squeeze through a hole this size, but they prefer a much bigger one, so it helps put them off.

⬇️ The drop from the hole to the floor

The bottom of the entrance hole should be at least 450mm above the nest floor. This is the most important safety measurement on the whole box. Owlets start jumping about and flapping long before they can fly, and a deep box stops them tumbling out. An owlet that falls to the ground is usually ignored by its parents.

🦉 What I do: in one of my taller barrel boxes, I've fitted a perch inside so the adults can look out of the hole. They really like it, and I think it encourages them to use the box. In a shorter design, I've put a small perch on the floor instead.

🥚 Floor area

This is where the eggs are laid and the owlets grow up, sometimes called the scrape. A good size is 0.25 to 0.5m², with 0.4m² as the target. Don't go below 0.2m². Barn owls don't build a nest, so the eggs go straight onto the floor, and old pellets soon build up into a soft layer.

🦉 What I do: my oak barrel boxes have a floor area of about 0.4m². To get that, you need a barrel around 700mm across.

🪵 Outside landing platform

A platform below the entrance hole is vital. The adults land on it when they bring in food, and it's where the owlets first see the outside world. Think of it as a balcony for the owlets. From there, they can climb onto the roof of the box and hop to nearby branches as they learn to fly. It needs to be at least 250 x 500mm, with a lip at least 100mm high so they don't fall off.

✅ Build checklist

Tick these off as you go. Your ticks aren't saved, so print the page if you'd like a copy for the workshop.

🖨️ Print this page

☔ Keeping it dry and long-lasting

• 💧 Waterproofing is everything. A damp box can chill and kill young owlets. Make sure the sides overhang the floor so rain runs off, and add a few small drainage holes just in case water does get in.
• 🏠 Protect the roof with thick roofing felt or another waterproof covering. I've fitted solar panels on some of my boxes, which also help keep the rain off.
• 🖌️ Treat the outside only. If your timber needs protecting, use a long-lasting, natural treatment such as beeswax on the outside. Never treat the inside, where the chicks will be. I use natural oak, which doesn't need any preservative at all.
• 🔓 Make it easy to clean out. I use hinged lids. You'll thank yourself when it's time to clear out old pellets.

📍 Choosing the right place

This is where many nest boxes succeed or fail. A perfect box in the wrong place will stay empty, while a simple box in the right place can be used within months.

• 🌾 Rough grassland is essential. The box should overlook rough, tussocky grass, which is where field voles live and where barn owls hunt. A pair needs a lot of it in the wider area: research suggests roughly 30 to 50 hectares (75 to 120 acres) of rough grassland within 2km of the nest in pastoral countryside.
• 🤫 Quiet and private. Barn owls don't like disturbance. Choose a spot away from busy footpaths, gardens, dogs and bright lights.
• 🏚️ Few other nest sites nearby. Your box has the best chance where there aren't many old barns or hollow trees for the owls to choose from.
• 🪶 A clear flight path. The owls need to fly straight into the hole without leaves or branches in the way.
• 🌬️ Face it away from the weather. Point the entrance away from the prevailing wind and driving rain.
• 🚗 Away from busy roads, as road traffic is one of the biggest dangers to barn owls, especially young birds.

🦉 What I've found: my boxes with the entrance facing north-west have been the most successful at attracting barn owls, and they stay warm and dry. It depends on your local weather, though, so look at which way the wind and rain usually come from where you are.

🏠🏠 Put up a second box nearby

This is one of my best tips. A second box, used as a roost, really does help encourage a pair to settle. It lets the male and female roost close to each other without always being in the same box, which barn owls seem to like, especially once the female is sitting on eggs.

🪜 Putting it up

• 🌳 In a tree: 3 to 5m up (10 to 16 feet). I find about 4.3m (14 feet) works well. Lower than that and predators such as stoats can reach it more easily.
• 📐 On a pole: use a pole at least 6m long with about 1.5m buried, so the box sits well above the ground. Pole boxes are ideal in open land with no trees or buildings.
• 🏚️ Inside a barn or building: an indoor box doesn't need to be as weatherproof, but it must never be used outside.
• 🍂 When: put boxes up in autumn or winter, outside the breeding season, so the owls have time to find them before spring.
• ⏳ Be patient. Some boxes are used within months. Others take a few years.

⚠️ Stay safe at height. Putting up a heavy box on a ladder is dangerous. Never do it alone. Get someone to help and hold the ladder, and think it through before you start.

🧹 Looking after your box

• 🧤 Clear it out when the debris gets deep (around 75mm), in the depths of winter, and only once you're sure the box is empty. Wear gloves and a dust mask, as old pellets are dusty.
• 🐦 Watch out for jackdaws. They love nest boxes and can fill them with sticks. If that happens, clear it out in winter so the owls can use it again.
• 🔧 Check it's still sound once a year: the fixings, the roof and the platform.

🚫 Please don't disturb an active nest. In the UK, barn owls are protected under Schedule 1 of the Wildlife and Countryside Act. Disturbing them at or near an active nest without a licence is an offence, so keep your distance during the breeding season. A camera is a great way to watch without disturbing them.

❓ Questions people ask

What size hole does a barn owl nest box need?

About 130 x 130mm is ideal. Anything from 100 to 150mm works. I use a 140mm hole saw.

How deep should a barn owl box be?

The bottom of the entrance hole should be at least 450mm above the floor, so young owlets can't fall out before they can fly.

How big should the floor of a barn owl box be?

Aim for about 0.4m², which is around 630 x 630mm. A good range is 0.25 to 0.5m², and it should never be less than 0.2m².

How high should a barn owl box go in a tree?

Between 3 and 5 metres (10 to 16 feet). About 4.3 metres (14 feet) works well.

Where is the best place to put a barn owl box?

Somewhere quiet and private, overlooking plenty of rough grassland, with a clear flight path to the entrance and few other nest sites nearby. A second box close by as a roost helps attract a pair.

Want to see what happens inside a barn owl box? Watch our live barn owl nest camera, or read my guide on putting a camera in your own box. For more expert advice, the Barn Owl Trust is a fantastic source of help.

Good luck with your box. I'd love to hear how you get on! 🦉

Paul