Home Improvement vs. Home Equity loan?

Here is my scenario:

In about two years I am likely going to need to either sell my home or add on to the one I currently have. For the sake of this post I am going to assume I will just stay put and add an extra bed/bath.

My original goal/plan was to save about 30k over the next two years to put toward the addition and then finance the rest with a home improvement loan. However, I'm wondering if it would be better to put all that extra money into the principal of my house and then instead taking out a home equity loan.

I could be way off on how this works but my thought process is that by paying that much more off the principal my monthly payments would go more toward principal rather than interest and increase my equity essentially giving me more money to use for the addition than just putting it all into savings.

I probably did a terrible job of explaining that but if it makes sense does anyone with financial knowledge have any advice on which would be the better option? Thanks.