Hello 

I am starting to do some research on adding a room to my basement. There was one already (house is 1979) but at some point there were water issues and the bottom studs were cut out. They also installed a basement technologies perimeter drain and two sump pumps. I have only heard the sump pumps going in 2019 when I brought the house after a very large snow year. Since then they have not kicked on. I am glad I have the drain and sumps, but it makes me feel better that they are not constantly on. Plus I have never seen the walls wet. 

Based on my reading here, conventional wall would be to remove the old studs, glue EPS to to wall but in my case I need it out enough to clear the drain. I saw a detain somewhere that brought the foam out using some sort of strapping, but I am now leaning towards dimple board, then EPS (Or foil backed), studs, etc. 

https://www.greenbuildingadvisor.com/question/basement-wall-and-floor-insulation-water-management

 A Builder friend recommended In-so-fast with rigid over it to get the R value. There are details on their website about installing it when you do the drain but not a retro-fit. 

https://www.insofast.com/explore/faq-insofast-and-perimeter-drainage-systems.html

Another question is what to do at the top of the wall at the joists, there are some good incentives for spray foam where I live (Vermont) but having just finished working on a LEED platinum building, it surprised me how anti-spray foam they were from a LEED perspective and life safety. 

Thanks, 

Chris