Angel - technically they cannot claim it as a deductino on tax as it is a capital improvement. you have to actually repair or replace an item to the same as before to claim as a deduction. They can depreicate it and claim the increase interest on their loan (if they extend it).
it can be done - I've done it before - major renovation for a capital improvement as a tax deduction (damn I love my accountant!)

hopefully you can get it sorted