Hi all first post so go easy. I’m building a shed / workshop and the base is ready for the fun bit. It’s 8x12 timber frame set on posts in postCrete. The underside is around 100mm off the soil. I’ll be insulating with 25mm Celotex then the floor boarding. I’m just wondering if it’s worth boarding or sheeting the underside of the base but is it really necessary? Maybe just some breathable membrane? Any suggestions welcome.