Whilst I have been sorting out the rest of the house the side door to
the garage and the threshold have been quietly rotting.

Garage floor is level with blocked patio alongside garage. Damp proof
course is one brick up. Wooden threshold is partly below garage
floor/patio level.

Just found whitish silky finish on threshold which may be dry rot?

Don't want to lower patio cos it would be a major job and it is
alongside 50 feet high ash tree that has roots under.

Opening from bottom of threshold to top of frame is about 208cm and
width is about 82 cm.

Is it best to treat all the brickwork and then put in a concrete
threshold or what?

Anyone know a source of reasonably priced doors and frames that would fit?

TIA for any replies.