Exterior beam rot can be structural. Treat it as a safety assessment first: temporary shoring and a qualified inspection beat cosmetic epoxy over a failing member.
Safety and scope
If the beam carries roof or floor loads and feels soft or has large hollow sections, bring in a pro. DIY epoxy fills are for limited surface rot after the member is confirmed sound.
Remove rot and dry
Cut or excavate soft wood. Allow thorough drying. Improve flashing, paint, and water shedding so the repair is not soaked again.
Repair options
Sistering a new member alongside, or full replacement, is the durable path for deep rot. Epoxy consolidants and fillers can stabilize shallow, non-critical damage when used exactly as directed.
Protect the repair
Prime, paint, or flash exposed wood. Maintain gutters and roof drainage that feed the beam.
For more repairs like this, start in the Rot & Outdoor Wood hub. If you are working through a related problem next, see Wood Decking Repair: How to Fix Cracked and Rotted Deck Boards or How to Fix Rotten Wood on the House: Exterior Siding Repair.
