Woodworm in Structural Beams: Risk, Treatment & When to Worry
Structural beams are the highest-risk place for woodworm. Learn how to inspect them, which species to look for, when timber is unsafe and what treatment means.
Beams and posts carry the weight of a building, so woodworm in them matters. Most cases are minor, but some are serious, and only a check will tell which. This guide explains how to inspect a beam, which beetles to look for and when to call a specialist.
How to inspect a beam
Use a torch and a screwdriver. Look at the whole beam, including the ends, because that is where damp collects. Check for holes, dust and soft wood.
Press the screwdriver into the surface in several places. Sound oak resists. Wood that gives way easily may have deep tunnels. Never lean on a suspect beam, because it may give way.
Which beetles to look for
Different beetles favour different beams:
- Oak beams in old buildings. Look for holes of about 2 to 3mm. Suspect the death watch beetle, which prefers damp, old oak.
- Softwood roof beams. Large oval holes suggest the house longhorn beetle.
- Softwood joists and posts. Small round holes are usually furniture beetle.
The species guide compares the clues.
When is a beam unsafe?
A beam may be unsafe if you see:
- Sagging or deflection
- Crumbling edges or deep tunnels
- Soft ends where the beam enters a wall
- Cracks that open under load
If you see any of these, ask a structural engineer or a specialist surveyor to look. Do not load the area until you have advice, since the beam may be weaker than it looks.
Why damp matters
Beam ends set into masonry stay damp. Damp softens the wood and invites both beetle and rot. For that reason, look at the ends first. The guide to woodworm versus dry rot explains how to tell the two apart.
How treatment works
Treatment usually combines a spray with boron paste, because paste reaches deeper into thick wood. In old buildings, the team may also dry the structure and fix the damp.
Weak beams may need repair or replacement. Options include splices, resin repair and new sections. A structural engineer should advise on load-bearing work.
Listed and historic buildings
Old beams may be protected. Work on a listed building often needs consent, so speak to the conservation officer first, because unapproved work can be an offence. Choose a specialist who understands historic timber.
What it costs
Costs vary widely. DampHub estimates £1,000 or more where large beams or several joists need replacing. See the cost guide for sources and ranges.
Next steps
Start with a survey, because it names the beetle and checks the strength. Request a survey when you are ready. You can also read woodworm in roof timbers.
Homes differ by city, so local advice helps. Our pages on woodworm treatment in Bristol and woodworm treatment in Leeds explain the usual problems.
To go deeper, read about the death watch beetle and the structural timber repair, because the right method depends on the beetle.