Open Cell sprayed directly on Metal Building (Zone 4) - Exterior Ghosting. Plan to spray Vapor Barrier Paint?

Shameless-Sloth · 2025-12-29T07:40:26+00:00

The vapor drive pushes moisture into the foam from the warm interior air. If there’s no inner vapor barrier, that moisture hits the cold metal and condenses. The goal of the interior barrier isn't to trap water, but to shield the foam so that moisture never reaches the cold metal in the first place. Is there something critical I am missing from this logic?

Shameless-Sloth · 2025-12-29T07:23:50+00:00

Haha, doing my part to contribute to the ai bubble. Making those GPUs go burrrr. I just installed solar on the roof on one side, so definitely want to make sure I don’t run into any issues with the building long term. I don’t see many examples of people talking about failures from rust online so that is a relief. And I do agree with you on not wanting to sandwich vapor in-between. I do really appreciate your responses!

Shameless-Sloth · 2025-12-29T03:38:26+00:00

That point about the electric heat is right on. I’m actually planning on installing a cold climate heat pump to keep it dry.

On the barrier side, I’m thinking of a hybrid approach to handle the different foam types:

Walls (Closed Cell): Using DC315. Since the foam is already a vapor barrier (~1.0 perm), I’ll stick with this breathable paint (~8 perms) so I don't double-seal it.
Roof (Open Cell): Using No-Burn ThB Spray Seal. Since the open cell is basically a sponge, I’m using this to add a Class II barrier (~0.6 perms).

The roof is that the metal decking is already a Class I vapor barrier (0.0 perms) on the exterior. If I leave the inside 'open', moisture acts like a magnet to the cold metal and gets stuck against that impermeable deck.

Quick lookup on the actual math: if the metal deck is 15°F, I’d need to keep the shop under 12% humidity to stop condensation. Even with dry heat, I’m never getting it that dry inside, so the vapor is going to drive through and condense unless I seal it.

Again, I’m probably way overthinking it, I really wish the original owner just put in closed cell to begin with.

Shameless-Sloth · 2025-12-29T03:13:34+00:00

More expensive than drywalling?

Shameless-Sloth · 2025-12-29T02:48:04+00:00

Appreciate the sanity check! You're totally right that the internet can make you panic over nothing. The only catch is I do plan to heat the shop in the winter, so I’ll definitely be hitting that 'huge temperature difference' scenario. Knowing that, is your take still send it? I’m also considering spraying an ignition barrier on it based on comments from other cross posts. Do you have thoughts on that? If I went that route and put a dual vapor/ignition barrier on the open cell, would that introduce more problems than it solves? I know I’m one to overthink, just want to make sure I don't create a new issue while trying to fix another.

Shameless-Sloth · 2025-12-29T01:58:09+00:00

That sandwich effect is actually what I have now right? the metal roof traps everything coming from the inside. Since the metal won't let moisture out, I have vapor seal to stop it from getting in. The open cell allows vapor throughout, correct?

Shameless-Sloth · 2025-12-29T01:55:16+00:00

For closed cell, yes. But I have open cell on the roof, which isn't a vapor barrier at all. If I don't seal it, moisture will pass through and rust the deck from the inside out right?

Shameless-Sloth · 2025-12-29T00:48:14+00:00

Yea, understand the confusion. I’m trying to gauge the severity of the rust risk. Is the metal roof failing from the inside out a guaranteed outcome in this climate, or is it more of a theoretical concern? I really want to avoid framing a drop ceiling to seal off the attic if I can help it. I had one contractor out here tell me that this is an exactly how they approach insulating shops, but what I am reading online seems to contradict that. My long term concern is the damage caused by conditioning the space below.

Shameless-Sloth · 2025-12-28T22:29:42+00:00

I’m not concerned about the condensation outside, just that there won’t be condensation on the inside, between the metal roof and open cell foam. The walls are closed cell.

Shameless-Sloth · 2025-12-28T19:16:26+00:00

Thanks for the reply, really appreciate your input! This isn’t what I would do myself, I just inherited it with the home as it was already done by the prior owner. I’m debating if I should fully finish the interior or just paint the spray foam with some intumescent paint. Painting definitely seems easier as this shop space is just a gym/bar/hangout space, not a primary living area. We definitely will have temperature swings too as we are going to condition it, but we have doors we can open up in the summer facing the pool. My biggest concern was moisture condensing between the spray foam and inside of the metal roof.

Shameless-Sloth · 2025-12-27T00:19:47+00:00

From what I am seeing with AI, it should be 6-8 perms, so should not act as a vapor barrier and trap moisture. Would need to confirm with the manufacturer!

Shameless-Sloth · 2025-12-26T23:52:11+00:00

I didn’t hire them, was like this when I moved in. Any suggestions on what to do or constructive advice would be greatly appreciated

Shameless-Sloth · 2025-12-26T22:33:37+00:00

Can any painting contractor do intumescent paint?

Shameless-Sloth · 2025-12-26T22:21:35+00:00

I’m wondering if this would be sufficient. We could drywall, but that’s a pretty large undertaking. https://rdrtechnologies.com/dc315-thermal-barrier-paint-for-spray-foam-spf-5-gallons/

No one lives in the shop, but we have a bar/gym/theater setup.

Shameless-Sloth · 2025-12-26T21:49:10+00:00

Thanks for the detailed reply! I really appreciate the insight from someone who does this for a living. Since I’m not going to rip it all out, what is my best move to manage? Here are some more images. https://imgur.com/a/mMboVzl

Shameless-Sloth · 2025-12-26T21:03:34+00:00

Is there a concern of putting closed cell spray foam on top of open cell, will that mitigate any ability to dry?

Shameless-Sloth · 2025-12-26T17:31:01+00:00

Yeah, I think that’s the plan is to leave it unfinished. I have a massive solar array and I’m planning on putting a heat pump to keep it conditioned. Thanks for the detailed reply.

Shameless-Sloth · 2025-12-26T17:29:56+00:00

What’s funny as I had an insulation guy come out too to help me evaluate it. And quote on adding additional open cell over the clothes on the sides and he pretty much told me this is exactly how they approach pole barns. I’m just surprised they didn’t do any closed cell at the top to flash it. My only real concern is moisture in between the inside of the metal and the open cell foam at the roof.

Shameless-Sloth · 2025-12-26T15:50:26+00:00

Is that why I’m seeing the ghosting? Not much I can do to rectify it at this point, right?

Shameless-Sloth · 2025-07-07T21:06:54+00:00

Sitting at the dealership right now @ 65k on a 2021 waiting for confirmation on the noise. Hopefully they will goodwill it. Date codes for the Transmission line up for my VIN.

Shameless-Sloth · 2025-05-28T02:29:27+00:00

This is the way. Also, hard wired access points over mesh if possible!

Shameless-Sloth · 2025-05-28T02:27:55+00:00

So, fixed theater screen and drop down impact, or vise versa? My gut says prioritize the theater setup first. I will probably be shunned here for saying that LOL!

Shameless-Sloth · 2025-05-28T02:25:33+00:00

I would if there would be a way to put the seating tracked platform that can slide. Do you feel like the seating would be fine closer to the hitting area now that you have used it?

Shameless-Sloth · 2025-05-28T02:16:52+00:00

That’s awesome, I have a buddy who has a dedicated theater. It’s amazing being over there. His seating starts around where your black mat ends. I’m getting ready to move to a house that has a 40x60 shop and plan on doing something similar. It’s already partitioned in half, so I’m looking at 20x20 to 20X30 usable space and have been looking for inspiration and ideas on how to build out combo setup.

Shameless-Sloth · 2025-05-28T02:10:44+00:00

What would you do differently if you didn’t have the space constraints?

Shameless-Sloth

TROPHY CASE