Can you get mortgages extensions based on the estimated value of your property AFTER you have had an extension built?

Struggling to get my head around funding our home improvement building project.

The simple answer is no. Its about your ability to pay back the money you owe, which has sod all to do with the value of your proerty.

However the value of the house IS important from the point of view that when you fail to repay the loan, the lender will want to make sure there is enough value in the home to pay off the debt.

they will loan against the agreed % of the house value (80% opr whatever) if you want to borrow a hogher percentage they will tend to charge a higher rate or refuse the loan.

You could ask for them to release funds as the value of the property increases durign the build process (potentially) – i.e they release funds at specific points in the build process for you to pay for the work.