Alas, not “rejoice, rejoice”.
When taking up the floorboards in the second bedroom today for the electrician, the builder discovered that the joists show water damage. He’s got the entire lot up now, and it looks like every joist in the back bedroom has suffered water damage to some extent, and all of them will accept a screwdriver being pushed in without much force applied; new wood, and older dry wood won’t accept the screwdriver end.
I won’t know until tomorrow morning what the approach will be to fix it – it’s either going to be a complete re-joisting, or a stitched re-joisting (which is what has been done in the master bedroom, and why they didn’t do both at once…).
The plumber will be around tomorrow as well, to run the water main through the bathroom wall, and we’ll discuss the feasibility of installing the stopcock in front of the house (underground in an insulated box with access hatch) and taking a T back down the trench to put in an outside tap on the studio.
The electrician handed me some bits of wire today, with chocolate block remains attached. Electrical wire is not mean to be blackened and stiff.
The builder also discovered yesterday that the porch roof beam isn’t actually set in to the wall like you’d expect. Instead, the bit of timber that the door is mounted to is what holds it in place. It’ll need an L-bracked, and then the timber can be removed for a DPC installation.
Pipe for the mechanical ventilation. The builder assures me this is how long it has to be 😉 
The beam for the porch roof; not attached to the wall 
The proposed solution – L-brace 
First discovery of damaged joists 
Dried-out wet rot; it’s not dry rot 
The grey wires should be grey and pliable, not black, and rock hard. 
That’s the tails from the meter.. barely under the plaster 
DPC installed around the porch 
All the boards up, and signs of damage on all joists 
A bit of damp in the back of the plaster, but dry now 
At least one of these has already been replaced!