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Redah
Member
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# Posted: 3 Apr 2025 10:31am
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The aim of this build is to have a continuous gap between the rigid foam board insulation (Tape Sealed. No Perforation) and the corrugated wall,
allowing cool or ambient air to circulate and vent
outside to prevent condensation during the winter, and excessive heat in the summer.
Should that air be coming from the outside?
Thanks!
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DaveBell
Moderator
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# Posted: 3 Apr 2025 05:58pm
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https://containermodificationworld.com/
https://www.youtube.com/@TheContainerGuyTV/videos
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toyota_mdt_tech
Member
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# Posted: 3 Apr 2025 09:37pm - Edited by: toyota_mdt_tech
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I'd use closed cell spray on foam in the air space.
I installed a container and added vents, 3 low on one side, 3 high on the other and put a roof on it with an attic and vented at gable ends and vents in every rafter block, it is free of any moisture and stays cool even on hot days. I have no insulation on the inside. Its just for storage.
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Redah
Member
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# Posted: 3 Apr 2025 09:55pm - Edited by: Redah
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Thank you for responding!
Spray is out of the question for us.
About where are you located?
Do you use any heaters during the winter?
This build will be in South Texas.
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Brettny
Member
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# Posted: 4 Apr 2025 04:35am
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If you cant spray foam starting with expensive shipping containers is something I wouldn't do.
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Redah
Member
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# Posted: 4 Apr 2025 05:01am - Edited by: Redah
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Brettny
The aim of this build is to have a continuous gap between the rigid foam board insulation (Tape Sealed. No Perforation) and the corrugated wall,
allowing cool or ambient air to circulate and vent
outside to prevent condensation during the winter, and excessive heat in the summer.
Should that air be coming from the outside?
Thanks!
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gcrank1
Member
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# Posted: 4 Apr 2025 11:45am
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Im wondering if you would be better off taking the intake air out of the ground rather than ambient air temp?
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Redah
Member
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# Posted: 4 Apr 2025 12:02pm
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Quoting: gcrank1 out of the ground rather than ambient air temp
As from under the house?
That's something worth contemplating. It might even help with cooling the walls and roof during the summer. I think you are on to something there.
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Redah
Member
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# Posted: 4 Apr 2025 12:20pm - Edited by: Redah
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DaveBell,
Thanks for the links.
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gcrank1
Member
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# Posted: 4 Apr 2025 05:04pm - Edited by: gcrank1
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I was thinking more like from some holes down into the ground, maybe kinda like what a ground source heat pump system uses but just moving the ground temp air? I know it is always cooler in my basement in the summer. Wonder how deep you'd need to go to hit a pretty stable ground temp?
Up here in WI in winter my only semi-heated basement temp near floor actually is about 54*f which is what I think the ground temp and ground water temp is. That floor is about 6' below grade.
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Redah
Member
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# Posted: 4 Apr 2025 05:19pm
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Quoting: gcrank1 more like from some holes down into the ground, maybe kinda like what a ground source heat pump system uses but just moving the ground temp air? I know it is always cooler in my basement in the summer.
I think you are on to something there. Let me think about this a bit more.
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toyota_mdt_tech
Member
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# Posted: 4 Apr 2025 09:02pm
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Quoting: Redah I think you are on to something there. Let me think about this a bit more.
I seen a cabin build show where they did just that. Dug a deep trench from under the floor to out in the woods, extended the pipe above grade with a weather head so no water can get in. A fan pulled air through the underground pipe and exited inside the cabin, the air was cool. Maybe warm when it entered, but lost all its heat as it went through the pipe underground.
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Redah
Member
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# Posted: 4 Apr 2025 10:26pm
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Quoting: toyota_mdt_tech Dug a deep trench from under the floor to out in the woods, extended the pipe above grade with a weather head so no water can get in
I also have seen that (in real practice). A neighbor cooled his Family Room/Kitchen that way. It wasn't even that sophisticated, complicated or hard to do. They had a 'hole' in the ground covered with a piece of plywood, with a 3" PVC pipe going into the house.
It was South Texas.
The year was 2002. The Gentleman was a 1st generation Polish American from Ohio, and the Lady was an English War-Bride.
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DaveBell
Moderator
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# Posted: 6 Apr 2025 04:10am
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I was in an earth cooled house once in summer Moorefield, WV. The house was definitely cool but too humid. Which could be fixed with a dehumidifier piped to drain outside. It was active with a fan somewhere. Do not know what size pipe was used or length. South Texas, I don't think the outside air is going to help much with the sun on a steel box. I would guess you would want the fan to pull air through the pipe, not push.
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Redah
Member
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# Posted: 6 Apr 2025 05:09am
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Quoting: DaveBell ... cool but too humid. ... South Texas, I don't think the outside air is going to help much with the sun on a steel box.
You're absolutely right about the humidity, and I will get back to that and the summer heat some other time.
As to the outside air idea, it's to equalize the air temperature of the cavity to prevent condensation during the winter (the whole 17 days of it).
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Steve961
Member
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# Posted: 6 Apr 2025 09:06pm
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As toyota_mdt_tech mentioned, a separate roof really helps keep the heat gain down. My cabin has a separate roof and it's amazing how little solar heat gain there is, although I do have spray foam inside my cabin. I also have a separate storage container without a roof and it gets really hot in there, and I'm in Wisconsin.
It's unfortunate you can't find a way to use spray foam, as it's amazing how effective it is with containers. It's almost like a thermos in how it keeps the cool inside in the summer. There's very few days that I wish I had air conditioning, but again, I'm in Wisconsin.
If you're set on your method, I'd make darn sure my vents are sealed up tight with the smallest, and most durable, insect mesh I could find. There's all sorts of insects that would love to make their home in your container walls.
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Redah
Member
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# Posted: 6 Apr 2025 10:20pm
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Quoting: Steve961 ... a separate roof really helps keep the heat gain down.
Thank you for responding.
The 'Heat' is not the issue here as of now. There are more ways to 'Tame' the heat that I know of than the heat being an issue. I'm more concerned with the so-called cold weather of South Texas and condensation.
For now, I'm trying to find the right way to keep the cold 'Skin' from creating condensation by equalizing the 'Gap" and 'Outside' temperature.
Thanks. I really do appreciate everyone's input in this.
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Redah
Member
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# Posted: 6 Apr 2025 10:29pm
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Quoting: Steve961 I'd make darn sure my vents are sealed up tight with the smallest, and most durable, insect mesh I could find.
You're definitely right about that.
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toyota_mdt_tech
Member
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# Posted: 7 Apr 2025 07:52am
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Quoting: Redah For now, I'm trying to find the right way to keep the cold 'Skin' from creating condensation by equalizing the 'Gap" and 'Outside' temperature.
Which closed cell foam would achieve.
What was the reason for not being an option?
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Redah
Member
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# Posted: 7 Apr 2025 08:06am
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Quoting: toyota_mdt_tech What was the reason for not being an option?
Just not for us.
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Steve961
Member
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# Posted: 7 Apr 2025 01:38pm
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Even with ventilation, there will be times when you get condensation on the interior walls of your container. A time will come when warm moist air passes through during the day, and then condenses on the interior walls on a cold night. You are then relying on the ventilation to evaporate the water droplets on the walls or floor the next day. IMHO this is a recipe for disaster.
I did a HUGE amount of research before I built my container cabin. The only 100% successful method to insulate a shipping container is with closed cell spray foam. I truly wish there was another way as I would have saved myself a lot of money and headache.
My advice to someone with your restriction would be, if you can't use spray foam then you shouldn't build with containers.
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Redah
Member
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# Posted: 7 Apr 2025 02:08pm
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Quoting: Steve961 A time will come when warm moist air passes through during the day, and then condenses on the interior walls on a cold night.
I've seen the scenario that you described happen in my little camper (converted Cargo Trailer) before.
I'll have to come up with another solution in the next 5 months prior to starting construction.
I'll keep watching this thread, just in case someone comes up with an idea.
Thanks for the input.
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Steve961
Member
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# Posted: 7 Apr 2025 07:11pm - Edited by: Steve961
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If you are still set on moving forward without spray foam, there is one other option, but it is not a 100% protective solution like spray foam. InSoFast makes foam insulation panels that are contoured to the corrugations of a container. They are not cheap, probably more than spray foam, and I would probably still want to foam or tape all the edges and seams.
The problem with these, and any other non-adhered insulation, is that if any moisture gets behind it, there's no way for it to get back out. Your vapor barrier to the container walls must be absolutely perfect to keep any and all moisture out.
If I did something like this I would also keep all my electrical and plumbing outside of the walls and be surface mounted. Cutting away the insulation could easily compromise the vapor barrier, and I don't even want to think what would happen if you had a plumbing leak and didn't see it.
Here's the link to their product:
InSoFast
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Redah
Member
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# Posted: 7 Apr 2025 07:30pm - Edited by: Redah
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Quoting: Steve961 If you are still set on moving forward
I'm most definitely going forward with the build. Just inviting ideas, tweaks and input from others.
You raised some points that I'll respond to some later time.
Thanks again!
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Redah
Member
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# Posted: 8 Apr 2025 01:00pm
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Quoting: Steve961 The problem with these, and any other non-adhered insulation, is that if any moisture gets behind it, there's no way for it to get back out.
Totally agree with you on the "non-adhered". I don't understand how anyone would think that InSoFast is anything but a scam.
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Redah
Member
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# Posted: 8 Apr 2025 01:05pm
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Quoting: Steve961 keep all my electrical and plumbing outside of the walls and be surface mounted.
That was the part of my plan which I was confident about. Take a look at the illustration in the initial post.
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Redah
Member
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# Posted: 8 Apr 2025 01:10pm
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Quoting: Steve961 Your vapor barrier to the container walls must be absolutely perfect to keep any and all moisture out.
Can you think of a possibility where a vapor barrier can be incorporated into my to 'fix' my idea?
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Steve961
Member
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# Posted: 8 Apr 2025 03:00pm
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Quoting: Redah Can you think of a possibility where a vapor barrier can be incorporated into my to 'fix' my idea?
Unfortunately no. Vapor barriers are meant to keep vapor away. You would be purposefully introducing sometimes moisture laden air in through the vents that would have direct contact with the bare container walls.
I have already seen this play out with my cabin in a unique way. While my interior cabin walls are insulated with spray foam, the exterior container doors that close are obviously not insulated. When I close up my cabin after a visit, I do leave the front windows cracked to equalize the pressure in that small space between the container doors and front wall/windows - think direct sun heating the doors and space behind. I also try and keep the humidity down inside when I am gone by using a fair amount of damp-rid.
Over time, spots of black mold have formed on the inside of the front doors, from what I would guess to be moisture from the inside air condensing on the cold steel doors at night. I do use a mold cleaner to remove it on occasion, but I'm sure I would have much more if I ever allowed enough high moisture outside air into that space.
OK, one more thought, although in some ways it does negate building with containers. Have you ever considered insulating the outside of the containers? Advantages are that you have "finished" interior walls, if you don't mind corrugations, in addition to much more usable space inside. All you have to do is attach some studs on the outside, place foam insulation between them, then add some siding.
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Redah
Member
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# Posted: 8 Apr 2025 03:11pm
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Quoting: Steve961 Have you ever considered insulating the outside of the containers?
Yes I have. That was my first, and moved to be "plan B" as of now.
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MtnDon
Member
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# Posted: 8 Apr 2025 04:58pm
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Quoting: Redah Should that air be coming from the outside?
Why would you not take ventilation air from the outside? The alternative would be air from the interior space. For many months of the year, the interior air will be conditioned, cooled, or heated. Moving that out through the wall ventilation would require that air be replaced with exterior air and reconditioned. A waste of energy, no?
******
I am very curious why spray foam is "out of the question" while rigid foam panels are okay. I can understand some people not liking foam at all, from an environmental aspect. If that is the case what type of foam sheets are you thinking of? Some of the newer foams (rigid sheet and spray) use newer blowing agents that have a reduced carbon footprint. Then there is also polyiso foam which is even better. More on that later.
I have serious doubts about how effective your proposed ventilation of the wall cavity would be. For one thing, I doubt there would be any meaningful ventilation of the ceiling space. The air would tend to just sit there in the horizontal space. The air in the wall space could rise as it warmed and vent out the top vents. I wonder how much air movement and moisture removal there would be on a cool day. Possibly this could work better with a forced air ventilation, but that needs energy.
A friend had a similar problem when he was contemplating the design of his new home about 15 years ago. He wanted to use concrete blocks to construct a strong wall. To make a long story short he insulated the structure on the outside. Furring strips of 2x4's were affixed to the exterior of the CMU wall. Then, three layers of rigid polyiso foam were applied to the exterior with staggered joints. 1x4 furring strips were affixed to some walls and a rain-screen, air gapped, with a finish wall of Hardi lap siding applied. Other walls were stuccoed. I would think something similar could be done on the exterior of the container. I believe that would be better than trying to invent a sure-fire method of ventilating between the inner and outer walls and ceiling. But that is only an opinion.
The thermal mass inside the envelope of the habital space has been a temperature moderating benefit.
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