I'm starting to plan my basement remodel project and one thing that I've been researching is hanging 1/2 inch polystyrene (XPS) insulation on the walls before I frame. The house is only 3 years old and the builders insulated the walls from the outside. I'm also not planning on insulating the floor. Is it necessary that I hang the XPS or am I just wasting time and money?

Thanks.

You should insulated your basement and XPS is good but I'd go a full 3" or 3.5" not just 1/2" It is going to be there forever and a warm basement makes a better family area. Do not insulate the first foot off the floor unless all basement walls are fully below the frost line. I would also put a 6 mil vapor barrier directly on the concrete tacked with dabs of liquid nails.