Any timber feature including doors, windows, roof structure etc that has suffered for one reason or another. The degradation tends to be due to water ingress creating a perfect environment for fungal or insect infestation. Surface rot does tend to hide the real extent of the decomposition.
A common mistake listed building owners make is when they initially identify the problem on the surface they leave the damaging process to continue to a point of no return as it doesn’t not look too bad.
We will be happy to come and see the issues and advise accordingly.