Bird's mouth cut
A birdsmouth or bird's mouth cut is a carpentry or timber roofing term for a small triangular cutout from a beam either at the end or along one side. It is made up of two cuts to remove a triangular piece of timber, the cuts are at 90 degrees to one another but their angle to the edge of the timber being cut will vary depending on the angle of the roof.
Birdsmouths are cut in to roofing rafters at the top to hang onto and be fixed to the ridge beam as well as lower don the rafter on one side to hang over the edge of the wall plate, making the top of the wall frame or lying on top of the wall if masonry of brick. The combination of the two cuts allows the rafter to sit at an angle to the horizontal beams creating the roof pitch.
[edit] Related articles on Designing Buildings
- Beam bridges.
- Beam formwork.
- Bond beam.
- Cantilever.
- Capping beam.
- Chilled beam.
- Collar beam.
- Flitch beam.
- Girder.
- Ground beam.
- Lattice beam.
- Metal web joists.
- Open web beam.
- Post.
- Rafter.
- Rolled steel joist (RSJ).
- Simply supported.
- Timber post and beam construction.
- Types of beams.
- Types of columns.
Featured articles
Check out some of the best features and news from Designing Buildings as well as key stories from around the web.
Government approach could undermine delivery and regeneration.
World's first mass timber data centre.
The overlooked environmental aspect of data centre development.
Introduction to radon awareness
New technical information sheet published by CIOB.
Updated supplier guide can help electrical contractors engage with NHP.
CIAT confirm the winners of the 2026 architectural technology awards.
Government launches a one stop shop for flood preparedness.
Sir Edwin Lutyens: Britain's greatest architect? Book review.
CIOB publishes free template to help assess and manage risks.
ECA's reflections on Party Conference season
Burnham wants to be confident of winning before asking for a fresh mandate.
New Chief Construction and Scientific Adviser
Sergio Cavalaro, Professor of Infrastructure Systems at Loughborough University.
Building safety levy for England
CIAT publish estimator tool for members.
Water sector faces a growing crisis that could slow the delivery of vital infrastructure.