Andy Hall wrote:

- Around any chimney stacks there will be either a lead flashing or
mortar benching from the stack onto the slates. Look around the
timbers inside for signs of water penetration or timber decay -
typically wet rot and perhaps weevil damage. From the outside with
binoculars take a look at the condition of the flashing/benching.

- If there is a rear extension, there will usually be a valley where
the roofs join, normally lead. Again look at as much of the timbers
inside as you can and the condition from the outside.


If you can, look in complete darkness for light shining in from outside.
Then look very carefully with a strong light for signs that rain has
blown in - or worse still, powder snow - at any time in the past. Don't
forget to check underneath the more recent loft insulation.

And while you're there, check the topside of the lath and plaster
ceilings.

Typically, you can get away with an unfelted roof for years, but then a
storm comes in from an unusual direction and suddenly you have a
problem. (Been there, shovelling snow into a kitchen bin, quick before
it melted into the loft insulation. Roof was stripped and felted the
next spring - money well spent.)


--
Ian White