What might be happening
Local decay may sit where a rafter meets a wall plate or valley; a stain alone does not establish loss of strength.
Roof timbers need to be examined alongside the roof covering, flashings and ventilation. A dark mark is not necessarily rot, but timber that has softened or lost strength deserves a proper inspection.
What you can look for
Inspect the roof covering above, roof-space ventilation and timber at bearings, not just the obvious patch.
You do not need to start taking the building apart yourself. If access is difficult, ask the person inspecting it to explain what needs to be opened up and why. Photographs of hidden defects are useful, especially when you are comparing quotations.
Putting it right
An appropriate repair depends on remaining section, loads and roof geometry; a carpenter and structural engineer may be needed.
Be wary of a quotation that deals only with the damaged wood and says nothing about the water or building defect behind it. Once the cause has been dealt with, the remaining timber can be checked and the necessary repairs planned.
When to call someone in
Do not cut or splice load-bearing roof members without competent assessment.
A carpenter or joiner may be right for a local timber repair. If the problem involves a leak, you may need a plumber or roofer first. Where supporting timbers have moved, sagged or seriously weakened, get advice from someone qualified to assess the structure.
Questions worth asking
- Where is water entering the roof, if there is a leak?
- Which timbers have actually lost strength?
- Will the proposed repair deal with the roof defect as well as the timber?