For our PPR mortgage, we switched to KBC and topped up. KBC would allow up to a 20K top-up with no questions asked, i.e. no requirement for quotes for the work. As 3 months passed between AIP and drawdown, we ended up drawing down 24K above what we paid off on our previous mortgage and KBC never batted an eyelid. Ulster Bank were very sticky about quotes to account for every penny of the top-up ... AND they said we could only drawdown the top-up parts by presenting the invoices ....we gave up on Ulster in the end.
OP, if your renovation can be done for ~25K, try topping up your home mortgage with KBC? We also got 3K cashback for switching. Not sure for how much longer this will be available.