Hi

I'm about to finish my basement. I have a french drain in my basement. So I was thinking about putting up a 6mm poly vapor barrier that would extend to the bottom of the wall to the top to help direct any moisture that collects into the french drain. I've pretty much resolved all the water coming through the wall by installing a french drain in my yard, but I thought I would be prudent and install a vapor barrier. A portion of the wall has a french drain and the other portion does not.

If I install a vapor barrier my only question is do I need to worry about ventilation in the wall? Should I install vents on the drywall side from the living space to the wall cavity? Or will that be asking for trouble? I read in some articles people are suggesting a product made by CertainTeed MemBrain that would act as a vapor barrier in the winter and allow moisture to escape in the summer time. I saw some people would install 6mm at the bottom 4 feet of the wall and then install this CertainTeed MemBrain on the top 4 feet. Is CertainTeed's product any good? Is it worth getting or should I just stick to 6mm poly?

https://www.certainteed.com/building-insulation/pr...

I'm an airframe engineer, so I thought I would ask my fellow engineers who specialize in HVAC for any advice. I've drawn up a picture of concept in Visio for feedback that I've converted into a PDF. I will be using 3.1" thick R-21 foam board that I've already purchased.

Many thanks. It is always good to get feedback.

Thanks,
Charles