Obviously we are assuming glasfryn had permission to do the work. You can't just do what you like and bill the landlord later.Work out what the landlord owes you and deduct it from your rent to pay in the next 3 months - this is far easier than trying to get money back. And don't fanny about with only asking for 50% either; it's the landlord's responsibility if building work needs doing or boilers need replacing.