ScrewMaster wrote:
Judging by the second picture it is dry rot.
You don't always get a fruiting body - I've seen plenty of rampant dry
rot and not a mushroom in sight.
You do often get the stringy white rhizomes - particularly visible
when you cut out the infected wood - it runs along between the brick
and the wood.
by law you are meant to cut out all timber 1metre beyond the any
evidence of the dry rot and replace.
The adjoining walls should be treated and treated timbers used in the
repair.
You can be held responsible if at a later stage your dry rot invades a
neighbour's property so it is especially important to properly deal
with any dry rot on or near a party wall.
dry rot spores lie dormant for many years/decades waiting for the
right conditions ie 40% moisture or above

Why do you judge it to be dry rot?

Dry rot isn't rampant, it spreads according to food source and moisture
content. A maximum is generally regarded to be 1m per year and even then
only under ideal conditions. Above 40% moisture??? More like above 22% and
it'll grow!!

While it's been suggested dry rot spreads more quickly in warm conditions,
it must be remembered that warm ventilated conditions imply dry wood where
dry rot cannot grow!

Dry rot spores tend to last 3 years, longer in cold conditions, shorter in
warm.

One charcteristic of dry rot is a brown dust. A very wet cotton wool like
structure and shrunken and dry looking cracked timber. These pictures show
wet rot!

If you've removed all signs of dry rot, it's unlikely you'd be responsible
for any further damage though it would be reasonable to inform your
neighbour so he can inspect his own timber. Dry rot tends to inflict
volumes with no access!

Remember dry rot needs mosture. As long as wood is in a ventilated area it
will not support dry rot. Moisture content is key.