Brendan's assertion that the value might only go up by c.50Ke is correct in my view.
Past cases I've seen would indicate that for 2e you spend on a refurb you get a value uplift of 1e(roughly).
On LTVs above 80% - AIB's green rate is 2.25%(5 yr fixed) & Haven's is 2.15%(4 yr fixed).
I'd have to double-check but I don't think Avant(which charges 2.15% for fixed rates) will lend against a future value of a property so it may not be a runner with this lender.
I don't know what your income level is so I can't comment on affordability.
As an existing mortgage holder, you will have to qualify for an exception if you are seeking a mortgage of more than 80% of the value of your property - which I think will be the LTV of your property even after the works.
Cental Bank limits apply once you are seeking to switch your lender & increase your borrowings - the limits(both the 80% LTV & 3.5 times salary) don't apply for straight switchers.
I hope this helps.
justin.griffith@mortgagebrokers.ie