Thoughts on staying indoors vs. leaving while using the BEEST kits?

I used the BEEST FullStop setup last summer for my crawlspace, and even with the vents open, that chemical odor drifted trough the floorboards almost immediately. While it’s a solid product for DIYers, the sheer volume of 18 cans being triggered one after another creates a significant amount of vapor. It isn't just about the person holding the gun; those isocyanates hang in the air during the curing phase, and a closed attic door rarely provides a perfect seal. My wife tried to stay in the kitchen while I worked, thinking she was far enough away, but she ended up with a scratchy throat and a headache within two hours. We ended up leaving for the night and staying at a local motel. For a project covering 360 board feet, you are looking at a lot of surface area off-gassing at once. If you can swing it, definitly pack a bag. It’s much easier to spend 24 hours away than to try and air out your upholstery once that heavy, sweet foam smell gets trapped in the house. Make sure he wears a full respirator too, because the fumes are intense in a confined attic space.

I did the same 18-can BEEST project in my ranch-style home last fall. Honestly, if you prep the attic hatch correctly, the smell shouldn't reach the main floor. We used a heavy-duty plastic drop cloth and painters tape to seal the ladder opening completely once he was up there. By keeping a high-velocity fan pointed out of the gable vent, it creates a negative pressure zone that pulls the fumes away from the house interior rather than pushing them down. People often run into issues because they don't account for the heat buildup in the attic during the curing. If your husband wears a proper respirator and you keep the HVAC system off so it doesn't circulate attic air, staying on the main floor is usually fine. I stayed downstairs the whole time we did our 400 square foot project and didn't notice much beyond a faint plastic scent for an hour. Just make sure he isn't blocking the soffit vents with the foam, or you'll have bigger moisture problems later on.

Have you ruled out your HVAC system as the primary culprit for spreading the smell? Even if you seal that attic hatch perfectly, any leaks in your return ducts—wich are common in older homes—will just suck those vapors in and distribute them to every room while the AC is running. I’d also be a bit skeptical about wether 360 board feet is actualy going to move the needle on your cooling bills. Are you sure you’ve addressed the bypasses and top plates first? If the goal is lower bills, spraying a thin layer without checking the duct integrity might just leave you with a smelly house and the same energy costs.

If you’re staying on the main floor, you’re definitely going to smell it. To handle the aftermath, I’d recommend setting up a Winix 5500-2 air purifier right by the attic stairs. It has a thick carbon filter that’s great for pulling those specific chemical VOCs out of the air. I ran one when I did my spray foam project and the smell was gone by dinner. Also, make sure he isn't just using a cheap dust mask; he needs a 3M 7502 respirator with the 6001 organic vapor cartridges to actually block those isocyanates. Better safe than sorry when you're triggering that many cans in one go.

Spot on about the smell drifting thru the floorboards. I'd absolutely pack that bag. One thing people usally miss with the BEEST kits is the temperture of the cans themselves. If your husband doesn't keep the cans between 75 and 85 degrees, the chemical reaction won't be complete, and that 'sweet' off-gassing smell will actualy linger for days instead of hours. If they're too cold, they won't mix right and you'll be dealing with a sticky, stinky mess much longer than the standard 24-hour window.

Quick update—we decided to play it safe. We sealed the attic hatch with plastic like suggested and ran an air purifier near the stairs. I’m glad someone mentioned the return ducts becasue we actualy shut the AC off entirely to keep the vapors from pulling thru the vents. The smell was there but manageable, and it cleared out way faster than I expected!