The simplest option is to get a home equity line of credit, also known as a HELOC, and basically what you’re doing is pulling equity out of your home as-is before the renovation.
The second option to consider would be a refinance of your home. Basically just refinancing your existing mortgage to pull out equity you have in the home.
The third option would be a renovation loan. This is a good option if the cost of construction is going to exceed the amount of equity. With this type of loan, the bank is going to be looking at the appraised value of the home after the renovation. Appraisers are going to look at both the square-footage of the home as well as quality of the space. Improving in either of these areas is going to get you a higher valuation which is going to allow you to get more financing from the bank.