12x30 Workshop About To Become A Reality

[Kent Adams]

I have a workshop nearly exactly your size and I live in Zone 7b/8a, so we have high heat and high humidity in the summer months. My walls are OSB with reflectix on walls and ceiling, vinyl on the outside with 6 foot french doors on the end and 36 inch single door on the long side. I use a window unit to keep it cool and it keeps it very cool. I monitor the indoor humidity with a weather station and it rarely gets above 60% humidity in the most humid conditions. My OSB has the reflective insulation and I put a similar foam type of reflective over the plywood floor and then 3/4 inch maple on top of that sealed with bona sport poly seal. All the joists were carefully insulated with r-13, both walls and ceiling with 1/2 plywood on top of that. I sealed every single corner, window and even joist with silicone. My shed is nearly airtight. A 2 ton A/C would be ridiculous for this space. I leave my AC on all summer and the bills are not that much. Because I leave it on all the time, I control the humidity ( a killer for anything with cast iron or hand tools). You need to rethink not leaving it on unless you're in the shop. A 2 ton A/C will cycle on and off so much you'll have extended periods of time where the humidity will rise in your shop before the motor kicks back on. Unless its variable speed, that motor will get killed in short order. I would fear you'll have all sorts of condensation build up inside your building unless you seal it properly and size the A/C properly. You don't need more than the most powerful 115v window unit to cool it. I lowered my ceiling to 8 feet as well and put r-38 on top of it. That vent you're talking about, which I have one in my greenhouse, will kill your ability to control humidity in that space. I know the guy is a friend, but he doesn't know what he's talking about in my opinion.

100 amp service panel should be fine along with 10/2 wiring. I have the same light fixture set up as well, you might want to make sure you space them wide enough to fit in an air filtration system on the ceiling.