Thoughts on spray foam sealing before adding rock wool?

I did the exact same thing when I converted my pole barn last winter. Trust me, you are not wasting your time. Rockwool is amazing for fire rating and sound, but it’s basically a giant air filter. If wind hits those metal panels, it’ll blow right through the fibers and kill your R-value. I used about thirty cans of Great Stuff Gaps & Cracks on my 2x6 studs before tucking in the Comfortbatt.

Dealing with the EMT conduit is a pain, I get it. I found that just hitting the major gaps where the girts meet the vertical posts made the biggest difference. You don't need it to look pretty since it's behind the wall. Once I finished and got the heater running, the difference between the sealed sections and the one corner I skipped was night and day. That canned foam stops the convective loops that make a garage feel drafty even when the thermostat says it is 65 degrees. Keep at it, your future self will thank you when the wind starts howling.

I honestly think you’re spinning your wheels with those cans. I tried that same approach on my 24x30 shop last summer, and it turned into a sticky mess that didn't help much once the seasons changed. Canned foam like Great Stuff often pulls away from metal panels over time because of how much the exterior skin expands and contracts in the sun. Instead of fighting with conduit and every tiny gap, you’d be better off focusing on a high-quality 6-mil poly vapor barrier or an air-tight drywall installation. If you press those R15 batts in tight, the friction fit is usally enought to stop the bulk of the air movement within the cavity. Using a dedicated house wrap on the exterior or even a layer of thin rigid foam board provides a more consistent thermal break than spot-sealing with cans ever will.

Also, think about the future maintenance. If you ever need to fish a new wire trough those boxes or add a circuit, you’ll be cursing that dried foam. I spent a whole afternoon carving out hardened gunk just to add one outlet in my garage. Just seal the major penetrations and let the Rockwool do the heavy lifting.

I'm totally with the first guy on this—air sealing is the secret sauce for metal buildings. One detail people ussually miss is how that foam helps with the rattle. Metal panels tend to vibrate or hum when the wind relly gets going, and that bead of foam acts like a dampener between the skin and the framing. It makes the whole structure feel way more solid and quiet. Just a tip: keep a can of acetone nearby for when you inevitably bump those conduit runs, it'll save your tools.

I am so pumped to see people actually doing this! I’m just starting to plan out my own workshop and I’m definitely going to try that foam trick now. It sounds like it makes a huge difference for the draftiness. While we’re talking about sealing things up, has anyone here ever used those shiny radiant barrier foils with rock wool? I saw a video where they layered them to keep the heat out during the summer. Would that be totally overkill if I’m already doing the foam and the batts, or would it actually help with the temperature? I'm just worried about trapping moisture if I add too many layers!

Since you're already doing the work, don't just stop at the studs. To really lock that garage down, you shoud be using DAP Touch ‘n Foam Professional Sealant around those electrical boxes and conduit penetrations. It handles the expansion and contraction better than the standard stuff. I used it on my last shop build before the Rockwool went in and it’s the only way to ensure those tricky spots don't leak. If you want a pro finish that actually lasts, getting a dedicated foam gun for those DAP canisters makes the detail work around the EMT way less of a headache.