How tough is it to get 25K extra added to a mortgage after full approval?

Hi,
I was hoping someone could help with a question I have - we are building a house on a site my parents gave us so, our loan to value ratio is very good. (Mortgage at the moment is 280 against a value of 395k).
We've had a few "surprises" during the build that have really put a dent in the budget and set us back by 25k.

We want to go back and look for the extra 25K from the bank, so, we can actually finish the build properly - does anyone know how difficult that would be? Would we need to go through the full approval process again? Or would we be better trying the credit union?

Thank a million!

I presume you have already started drawing down the mortgage, if you have you may have to wait until it is fully drawn down and apply for a top up loan. Amalgamating the new amount into the existing probably would result in a full new mortgage. Obviously it will depend on income as well.

I would try the bank first before going to credit union simply because the rate will be better and term longer.