How to Build and Install Custom Bat Exclusion Netting Flaps

A practical guide to creating and fitting one-way netting flaps for safe, humane bat removal from your property.

By Garret Merkley · Explainer · Jun 4, 2026

Branched from Humane Bat Exclusion from Georgia Home Eaves: Timing, Devices, and Histoplasmosis Safety

Quick take

Bat exclusion netting flaps are one-way devices allowing bats to exit a structure but not re-enter.
Custom-built flaps ensure a perfect, sealed fit for irregular or unique entry points.
Always install these flaps before bat maternity season (typically spring/early summer) to prevent trapping flightless young.
Ensure the netting hangs freely, extends sufficiently, and all other entry points are sealed before installation.

A bat exclusion netting flap is a simple, humane device designed to allow bats to exit a structure, such as an attic or wall void, but prevent them from re-entering through the same opening. It acts as a one-way valve, typically made from lightweight netting, ensuring bats can safely leave their roost without being able to find their way back in.

Understanding the One-Way Principle

The core idea behind an exclusion flap is gravity and a clear path. Bats, when leaving a roost, usually drop down and fly out. The netting flap is installed to hang loosely over their exit point, extending downwards. When a bat drops out, it passes through the netting. However, when it attempts to return, the netting blocks its path, and the bat cannot push its way back up or through the secured top. This forces them to seek an alternative, natural roosting site.

Building Your Custom Netting Flap

Custom flaps are essential when dealing with irregular openings, such as gaps in soffits, loose fascia boards, or unique architectural features that bats exploit. A generic device might leave gaps, allowing re-entry or trapping bats.

**Materials:** You'll need lightweight, durable netting (polypropylene or polyethylene mesh, typically 1/4 to 1/2 inch), a sturdy but light frame material (e.g., thin wood strips or PVC pipes), heavy-duty staples or screws, caulk, and a measuring tape.
**Measure Precisely:** Carefully measure the exact dimensions of the bat entry point. Add a few inches to the width for overlap and at least 18-24 inches to the length for the netting to hang freely below the opening.
**Construct the Frame:** Build a simple rectangular frame from your chosen material that is slightly larger than the entry point. This frame will be secured to the building around the opening.
**Attach the Netting:** Secure the top edge of your cut netting to one side of the frame using staples or screws. Ensure the netting hangs straight and freely, without any snags or obstructions.

Installing the Flap Correctly

Proper installation is crucial for the flap's effectiveness and the bats' safety. Before installing, you must identify and seal all other potential bat entry points on the structure. This ensures bats only have one way out.

**Seal All Other Gaps:** Thoroughly inspect the entire building for any other small cracks, holes, or openings bats could use. Seal these completely with caulk, mesh, or other appropriate materials. This step is critical; if other entry points remain, bats may simply move to another spot or be trapped inside.
**Position the Flap:** Place your custom-built frame over the main bat entry point, ensuring the netting hangs freely and extends at least 18-24 inches below the bottom edge of the opening. The top of the frame should be flush against the building, completely covering the entry.
**Secure Tightly:** Fasten the frame securely to the building using screws or staples, making sure there are no gaps between the frame and the structure where bats could squeeze through.
**Clear Drop Zone:** Verify that the netting hangs freely and that there is an unobstructed drop zone below the netting. Bats need to be able to drop and fly away without hitting obstacles like bushes, ledges, or the ground immediately below.
**Monitor and Remove:** Leave the flap in place for approximately 5-7 days (longer during colder weather, up to 10 days) to ensure all bats have exited. Once you're certain no bats remain, remove the flap and permanently seal the original entry point.

Building and installing custom bat exclusion netting flaps is a key step in humane bat removal. It matters because it provides a safe, stress-free exit for bats, preventing them from being trapped inside your home, which is both inhumane and can lead to unpleasant odors. This method also prevents re-entry, solving your bat problem long-term. This process applies whenever you discover bats roosting in your home and need to encourage them to leave without harming them. The most critical timing consideration is to **never install exclusion devices during bat maternity season**, which typically runs from late spring through late summer. Installing during this period would trap flightless young inside, leading to their death and potential health hazards for residents.

Critical Timing for Bat Exclusion

Always install exclusion devices *before* bat maternity season (typically early spring) or *after* pups are flying (late summer/fall).
Never exclude bats during maternity season, as flightless young will be trapped inside and die.
Check local wildlife calendars or consult a wildlife expert for specific dates in your area, as they can vary.

How long should I leave the netting flap up?

Typically, you should leave the netting flap in place for 5-7 days to ensure all bats have exited. In colder weather, bats may be less active, so extending this to 7-10 days is advisable to account for their slower movements.

What kind of netting should I use for an exclusion flap?

Use lightweight, durable polypropylene or polyethylene netting with a mesh size small enough to prevent re-entry (e.g., 1/4 inch to 1/2 inch). The material should be dark-colored to be less visible and sturdy enough to withstand weather, but flexible enough to hang freely.

Can I use this method for any bat entry point?

Netting flaps are most effective for distinct, larger openings like gaps in soffits, gable vents, or chimney openings. For very small cracks or crevices, it's generally better to seal them directly after confirming all bats have exited, as a flap might not fit or be effective.

What if I see bats trying to get back in after installing the flap?

If bats are attempting to re-enter, it indicates either the flap is not installed correctly (e.g., not hanging freely, too short, or has gaps), or there are other unsealed entry points on your home. Thoroughly re-inspect your installation and the entire structure for any overlooked access points.

Sources

General guidelines for humane bat exclusion from wildlife organizations and pest control resources.