Is it normal for Prodex insulation to have huge air gaps behind the panels?

You basicly just paid thousands of dollars for bubble wrap. The biggest problem with Prodex and similar reflective products is that thier advertised R-values are based on the entire wall assembly in a perfect laboratory setting, not the material itself. They rely on an air gap to function as a radiant barrier, but in a metal building, those gaps are rarely sealed. If air is moving behind those sheets, the thermal performance drops to almost nothing.

Those gaps you see between the sheets and the framing are going to be your undoing when the humidity kicks in. In a steel building, you have a massive thermal bridge. Without a continuous airtight seal against the metal, warm moist air is going to hit that cold steel skin and condense. I've seen buildings where the condensation got so bad it looked like it was raining inside, despite the shiny foil on the walls. Once that moisture gets trapped in those 'dead spaces' your installer mentioned, you're looking at mold and rust issues before the year is out.

If you want to salvage this without a total tear-out, you need to go back and tape every single seam with high-quality foil tape and try to seal the perimeter. But even then, you aren't getting anywhere near the performance of closed cell foam. Most guys who go this route end up frustrated because the building still feels like an oven in July. The R-value of that stuff alone is usually less than R-5, whereas two inches of closed cell would have given you R-13 or higher and a permanent vapor barrier.

At this point, you should probably cut your losses before you spend more on 'spacers' or finishing work. If you can afford to pivot, ripping it out and spraying **closed cell foam** directly to the steel is the only way to truly bridge those gaps and stop the thermal transfer. It's a hard pill to swallow, but it's better than watching your equipment rust because of a glorified radiant barrier.

While the previous poster correctly identified the assembly issues, one must also account for the inevitable degradation of the foil's low-emissivity surface due to atmospheric dust accumulation within those unsealed cavities, as even a microscopic layer of particulate matter significantly increases the emissivity coefficient and effectively nullifies the radiant barrier's primary mechanism of heat rejection. Furthermore, if your installer utilized mechanical fasteners that penetrate the steel girts without thermal breaks, you have essentially created thousands of tiny thermal conduits that will facilitate conductive heat transfer regardless of the reflective properties of the material, leading to localized cold spots where condensation will preferentially manifest even if you manage to tape the seams perfectly.

I went thru this exact nightmare with my 30x40 last year. I tried to save five grand by using the foil rolls instead of foam, and within three months, I had puddles on my workbench from the ceiling sweating. Taping the seams helped a tiny bit, but it didn't stop the heat—my shop stayed at 95 degrees all afternoon. I finally bit the bullet, ripped it all down, and had a crew spray 2 inches of closed cell. The difference was night and day instantly. If you're seeing gaps now, your shop is going to be a sauna. Honestly, just pull it now while it's clean and sell the rolls on Craigslist to someone doing a small van build.

Have you ruled out the ventilation setup in the peak of the building before you decide to rip everthing out? Everyone jumps straight to the insulation material being the failure, but I've seen plenty of steel shops where the 'raining inside' problem was actualy a lack of ridge vents or a powered exhaust to pull that humid air out. If your air turnover is zero, even foam can have issues with surface moisture. Are you sure the gaps you're seeing aren't just a result of the building settling or the initial tensioning? Might be worth checking if your humidity levels are spiking because of the slab curing or outside air infiltration before you write off the whole investment.

Quick update—I checked the ridge vents like suggested, and they're clear, but it’s alredy hitting 90 degrees in here. I tried taping a few seams to stop the sweating, but that point about dust ruining the R-value has me worried. If the foil stops working the second it gets dirty, am I just fighting a losing battle with these air gaps?