Disclosure - i work for a mortgage intermediary.
Some Lenders will alllow you to take the main mortgage out over a standard term (eg 25 or 30 years) and take a smaller mortgage €10k for example over a shorter term (eg 5 years).
"Mix n’ Match Terms – This feature simply allows you to split a mortgage over different terms. This feature is ideal for people who like the idea of raising cash at mortgage rates of interest, but who do not wish to spread the borrowing over the full term of the mortgage. "
So you could possibly take the renovations out at mortgage rates but not have them run over the full term of the mortgage.....
cheaper than securing an unsecured loan from a retail bank