u/wanderounder

I am the proud new owner of a old barn. The space has been partitioned into three separate rooms on the bottom floor with an upstairs loft.

I want to make this into a proper workshop, with ventilation and insulation. This structure has been exposed to the elements for decades and I want to extend its life and make it more useable. There’s power already and no need for plumbing, I won’t be living there. Is there a way for me to waterproof the existing building as it stands? What do I need to do before adding insulation and drywall?