Rot follows the same rule. Fix the water and you remove the conditions; treat the timber without fixing the water and you are buying time, not a solution.
Signs of an active infestation
Clean, bright holes with sharp edges and fresh, gritty frass below them suggest recent emergence. Old holes are dark, dusty and weathered, and the frass under them is compacted and grey.
Emergence is seasonal, so the clearest evidence usually appears in late spring and early summer. Damp readings in the surrounding timber are as telling as the holes themselves.
Wet rot and dry rot are not the same problem
Wet rot stays where the water is. Remove the source, dry the area, cut out and replace the failed timber, and it is done.
Dry rot can spread through masonry to find new timber, so the scope is wider: tracing the growth, removing affected material well beyond the visible edge, and eliminating the moisture path that fed it. Correctly identifying which you have changes the cost of the job substantially.
What we do about it
Structural first: assess whether the affected timber still does its job, and splice or replace bearing ends and rafters where it doesn't. Then moisture: gutters, flashings, ventilation, ground levels.
Chemical treatment has a place as a targeted measure, not as a blanket spray over a roof that has been dry for fifty years. We will tell you when it isn't needed.
Common questions
How do I know if woodworm is still active?
Fresh, pale-edged holes with clean frass, especially in late spring, alongside damp timber. Old dark holes in dry timber generally mean the infestation is long finished.
Does woodworm weaken structural timber?
Heavy sustained activity in sapwood can, especially in joist ends and rafters. Scattered historic holes in dry timber usually have no structural consequence.
Is dry rot really that serious?
It is the one to take seriously, because it can travel through masonry to reach new timber. It still needs moisture, so the fix always includes removing the water source.
Do I need a chemical treatment?
Only where activity is current and moisture has been dealt with. Treatment without drying the timber does not hold.