Rotten wall plate replacement

[Justs]

Following a failed gutter for many years, both the wall plate and brickwork above the first floor front of house window are damaged. Wall plate rotten at the middle (about 500mm section), mortar all loose (see pictures). As a result, the flat area over straight bay window is slightly sunken.
Builder who came by to fix suggested cutting off the damaged wood section, replace just that section with good wood, splice the lot together and screw onto the three sections of wood (the ones now forming the wallplate) an "L" shape angle metal plate. Plus, of course, repointing the bricks under the plate.
Is this suggestion sound work? Or it is imperative (maybe even legally/standards/regulations required) that the rotten wall plate has to replaced with a WHOLE length of solid timber?
Many thanks!

 

[Deleted member 174758]

Builder who came by to fix suggested cutting off the damaged wood section, replace just that section with good wood, splice the lot together and screw onto the three sections of wood (the ones now forming the wallplate) an "L" shape angle metal plate. Plus, of course, repointing the bricks under the plate.
Is this suggestion sound work? Or it is imperative (maybe even legally/standards/regulations required) that the rotten wall plate has to replaced with a WHOLE length of solid timber?

I have done a few partial replacements in a similar manner on council-owned listed buildings under instruction from the structural engineer with the approval of the council's Clerk of Works and Conservation Officer. For a job I should have started on in April this year, exactly the same approach was agreed for another grade II listed building where there were two sections of rot to cut out.

To replace a section I'd cut some angled blocks to go onto the underside of the rafters and fix them to the affected rafters near to the wall (so as to provide a level surface and allow you to get a scaffolding tower in there - this is not a job to tackle off a ladder). Acrow props can then be screwed to these angle blocks and used to lift the roof just slightly (a few millimetres - this is only to take the pressure off the wall plate, lift too much and you'll potentially do a lot of damage). The rotted section of the wall plate is cut out using a recip saw and demolition blades (recommend Milwaukee) taking care not to damage the rafter ends, especially the birds mouths. The nails used to fix the rafters to the wall plate may need to be cut out with a grinder. The replacement section should be of treated timber, if softwood, and sit on a piece of DPM. Cut ends must all be treated before installation. The end connections to the existing wall plate can be a simple lapped connection. Once the new section is in place and fixed to the old sections the Acrows can be lowered to allow the rafters to sit onto the new wall plate. At that point if the tiles/slates are still in place you'll need to secure the rafters to the wall plate using something like 90mm angle plates and screws (may require an angle drill or angle driver). TBH this job is far easier to do if the roof covering is off. Warning: In the process of doing this job if your significant other is within earshot they may find that their Anglo-Saxon vocabularly is somewhat enlarged... In other words it can be a b'stard of a job to do, but is well within the capabilities of a keen DIYer IMHO

 

[^woody^]

If you have stopped the leak you have stopped further damage to the timber.

Treat with preservatives and leave it.