My friends dog is usually quite good, but recently he's been weeing in the house.
Luckily there is wooden floors, but it's extremely irritating.
A family member has recently moved out, could the stress have upset the dog?
Any advice helpful

Sounds either medical or behavioural - check with vet first to exclude UTI or diabetes etc - Good luck

The vet could also refer to a reputable behaviourist, if required.

A vet visit is certainly in order.

One of Murphy's symptoms when the vet queried Cushing's was excessive thirst and excess peeing. At that point he hadn't had any accidents, but before we got the definitive diagnosis he did have a few. Since being on medication for the Cushings - no accidents at all.

Not saying it is Cushings as there are other illnesses that can lead to accidents from a simple UTI to Diabetes, just giving it as an example as why a vet visit is in order.