If you take out the loan, and are making the repayments, then the repayments will be deducted from your income for the means assessment. It will be a matter of showing that you are making the repayments.
If you still haven't started the work, and the loan principal is sitting in your bank, then you will be assessed as having that capital, although for a couple the capital limit that applies for medical card means assessment is 72,000 so unless this pushes you over that amount, it won't make any difference.
If you are in receipt of any other means tested social welfare payment, the money sitting in the bank may also affect your payment.
I certainly wouldn't advise anyone to take out a home improvement loan to get a medical card, but if you're going to take one out, you may as well get the deductions that you are allowed.