Posted: 6/11/2026 9:22:48 PM EDT
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I'm to the point where I'm ready to do start doing something about insulating the new garage. Garage was a kit built from 2.25" galvanized tubing with metal siding. I got the optional insulation, expecting that I would be getting the style of insulation with a vapor barrier and fiberglass attached to it. Instead, what they supplied was a thin version some kind of bubble / foil stuff. One side is foil, the other side is a white plastic membrane with the air pockets. Really thin. I've been doing some research, but I've gotten mixed results which leaves me a bit confused. The stuff they have installed acts as a vapor barrier, similar to house wrap, but I doubt that it breaths. I want to put rockwoll in the cavities. Spray foam really isn't an option right now. One search says to cut the R9 stuff to allow the wall to breath because in very cold climates, the warm air inside would condensate when it meets the cooler steel siding. Makes sense to me. Then another article says to leave the R9 stuff intact, and to tape all the seams and any other areas that air could get in and that, since I live in an area that gets very mild winter and hot summers that the condensation wouldn't be an issue because the wall will be able to breath. The added complication is that I want to eventually run a couple of courses of plywood on the lower sections of wall. |
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SC isn’t too cold. Condensation in the summer won’t be an issue unless you install AC and run it really cold. Whatever you do, do NOT use an unvented gas/propane/kerosene/diesel heater. They aren’t as bad in the dry areas of the west but in humid areas of the east, they will introduce too much moisture and you will get condensation inside your walls on the exterior metal when it gets cold. For your area, a mini split heat pump would be perfect. Is this building the horizontal metal sheets for an exterior? If so, it’s going to be a challenge to insulate. Unfortunately, spray foam will be the best option to insulate it NOW. Did they put on the bubble foil first and then cover the frame with the metal? If you can’t or don’t want to use spray foam, then your next best option would be to frame the walls on the inside and then insulate like normal with batts. You could install studs on 24” centers and then cover with OSB or metal sheets. |
"It behooves every man to remember that the work of the critic is of altogether secondary importance, and that, in the end, progress is accomplished by the man who does things."
Theodore Roosevelt
Theodore Roosevelt
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Originally Posted By ColtRifle: SC isn’t too cold. Condensation in the summer won’t be an issue unless you install AC and run it really cold. Whatever you do, do NOT use an unvented gas/propane/kerosene/diesel heater. They aren’t as bad in the dry areas of the west but in humid areas of the east, they will introduce too much moisture and you will get condensation inside your walls on the exterior metal when it gets cold. For your area, a mini split heat pump would be perfect. Is this building the horizontal metal sheets for an exterior? If so, it’s going to be a challenge to insulate. Unfortunately, spray foam will be the best option to insulate it NOW. Did they put on the bubble foil first and then cover the frame with the metal? If you can’t or don’t want to use spray foam, then your next best option would be to frame the walls on the inside and then insulate like normal with batts. You could install studs on 24” centers and then cover with OSB or metal sheets. The metal sheets are installed with the ribs running vertically and the skeleton is 52” centers, so my plan was to insulate with rock wool bats but run them horizontal then cover it with plywood, predrill and use wood to metal screws. My biggest concern is condensation not being able get out and causing mold and rot. I am probably over thinking this and it’ll be fine to leave the exterior insulation/vapor barrier in place. Or I just man up and install an exhaust fan and crack the roll up door for a breeze |
| First thing to know is the foil insulation a vapor barrier or just a house wrap. This is the critical question. House wrap and vapor barrier are not the same. If the foil insulation is a vapor barrier, it would need removed or perforated in order to add insulation inside of it. |
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Originally Posted By fulminate: The metal sheets are installed with the ribs running vertically and the skeleton is 52” centers, so my plan was to insulate with rock wool bats but run them horizontal then cover it with plywood, predrill and use wood to metal screws. My biggest concern is condensation not being able get out and causing mold and rot. I am probably over thinking this and it’ll be fine to leave the exterior insulation/vapor barrier in place. Or I just man up and install an exhaust fan and crack the roll up door for a breeze Moisture will condense on cold surfaces. In the winter, that’s the metal. The bubble foil will help. Honestly, SC is in HVAC zone 2 and some 3. So, winter moisture really isn’t a major concern. If you can put batts in the wall and cover it with plywood, that’s what I would do. I doubt you’ll have any moisture problems as long as you don’t use unvented heaters. Might be an issue if you run AC in there in the summer too cold. But, if you cool it to like 72-75, you won’t have condensation issues in the wall and the AC will also dehumidify the interior. Maybe run a dehumidifier if you don’t want to run AC. I’d put batts in the wall, close it up, and not worry about it. If you lived in a colder climate I’d make different recommendations but for your climate, I wouldn’t be too concerned with winter condensation. Leave the bubble foil in place. It won’t hurt anything and your building will dry to the interior. Just keep the interior reasonably dry and you will never have any issues. Insulate it….install a mini split of the appropriate size, and you’ll be loving life. |
"It behooves every man to remember that the work of the critic is of altogether secondary importance, and that, in the end, progress is accomplished by the man who does things."
Theodore Roosevelt
Theodore Roosevelt
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Originally Posted By crazyelece: First thing to know is the foil insulation a vapor barrier or just a house wrap. This is the critical question. House wrap and vapor barrier are not the same. If the foil insulation is a vapor barrier, it would need removed or perforated in order to add insulation inside of it. Bad advice for a warmer climate like the OP. Be different if he was in a colder climate like yours. Insulation does not perform the same based on heating needs vs cooling needs. OP is a primary cooling area so simply insulating is fine vs a primary heating area where a proper application of a vapor barrier is FAR more important. |
"It behooves every man to remember that the work of the critic is of altogether secondary importance, and that, in the end, progress is accomplished by the man who does things."
Theodore Roosevelt
Theodore Roosevelt
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Originally Posted By ColtRifle: Moisture will condense on cold surfaces. In the winter, that’s the metal. The bubble foil will help. Honestly, SC is in HVAC zone 2 and some 3. So, winter moisture really isn’t a major concern. If you can put batts in the wall and cover it with plywood, that’s what I would do. I doubt you’ll have any moisture problems as long as you don’t use unvented heaters. Might be an issue if you run AC in there in the summer too cold. But, if you cool it to like 72-75, you won’t have condensation issues in the wall and the AC will also dehumidify the interior. Maybe run a dehumidifier if you don’t want to run AC. I’d put batts in the wall, close it up, and not worry about it. If you lived in a colder climate I’d make different recommendations but for your climate, I wouldn’t be too concerned with winter condensation. Leave the bubble foil in place. It won’t hurt anything and your building will dry to the interior. Just keep the interior reasonably dry and you will never have any issues. Insulate it….install a mini split of the appropriate size, and you’ll be loving life. This makes sense to me. Thanks for the replies and for your time. |
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Originally Posted By fulminate: This makes sense to me. Thanks for the replies and for your time. Originally Posted By fulminate: Originally Posted By ColtRifle: Moisture will condense on cold surfaces. In the winter, that’s the metal. The bubble foil will help. Honestly, SC is in HVAC zone 2 and some 3. So, winter moisture really isn’t a major concern. If you can put batts in the wall and cover it with plywood, that’s what I would do. I doubt you’ll have any moisture problems as long as you don’t use unvented heaters. Might be an issue if you run AC in there in the summer too cold. But, if you cool it to like 72-75, you won’t have condensation issues in the wall and the AC will also dehumidify the interior. Maybe run a dehumidifier if you don’t want to run AC. I’d put batts in the wall, close it up, and not worry about it. If you lived in a colder climate I’d make different recommendations but for your climate, I wouldn’t be too concerned with winter condensation. Leave the bubble foil in place. It won’t hurt anything and your building will dry to the interior. Just keep the interior reasonably dry and you will never have any issues. Insulate it….install a mini split of the appropriate size, and you’ll be loving life. This makes sense to me. Thanks for the replies and for your time. One amendment to the above and one of your posts: use self-tapping screws. They’ll go through the OSB just fine and will keep you from having to pre-drill. I’d use at least #8 screws with either some kind of washer head or add washers to help them hold the OSB because depending on how you install the rockwool you’ll be happy to have a little extra holding strength if the insulation is pressing against the OSB sheets. |
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Originally Posted By Quicky06: Sounds like all you know is piss pour installation/Building science. Originally Posted By Quicky06: Originally Posted By Greenspan: All I know is spray foam seems like nothing but an air quality and home disaster Sounds like all you know is piss pour installation/Building science. I’m thinking he means the tightness would cause stagnant and bad air quality. I’d rather it be sealed tighter than virgin’s twat. And then control how much air you let in and out. And I don’t mean a fake virgin like those silly Mormons who think you can put in and if you don’t move it doesn’t count. I mean the real deal, young southern Christian girl who waits until marriage. I’m building right now and I’m trying to basically build a large cooler. |
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Originally Posted By First-World-Problems: I’m thinking he means the tightness would cause stagnant and bad air quality. I’d rather it be sealed tighter than virgin’s twat. And then control how much air you let in and out. And I don’t mean a fake virgin like those silly Mormons who think you can put in and if you don’t move it doesn’t count. I mean the real deal, young southern Christian girl who waits until marriage. I’m building right now and I’m trying to basically build a large cooler. I don’t disagree but this is a garage. Even the best garage doors leak air like crazy compared to a wall. Spray foam would do well in this case but batts will do fine too. Too tight is never an issue with garages. |
"It behooves every man to remember that the work of the critic is of altogether secondary importance, and that, in the end, progress is accomplished by the man who does things."
Theodore Roosevelt
Theodore Roosevelt
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Built a 45x90 stick build covered in metal(barndo, but not a true barn build) 1/2 shop 1/2 house, 35x40 loft/attic storage finished and floored. 2x4 walls filled and 2x6 ceiling purlins filled with open cell, shaved to the stud. Not real excited about it as we are having huge condensation issues. I'm running a dehumififier about 8-20 hours a day, along with AC. Not sure what to do at this point other than dehumidify all day long. Not sure if fiberglass bats would have been better but i'm just frustrated. Edit; spelling |
AcidGambit, I’ve always wanted to milk a lactating chick... Like make her get on her knees, milk her tits, and make her moooo.
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Originally Posted By mouthpiece: Built a 45x90 stick build covered in metal(barndo, but not a true barn build) 1/2 shop 1/2 house, 35x40 loft/attic storage finished and floored. 2x4 walls filled and 2x6 ceiling purlins filled with open cell, shaved to the stud. Not real excited about it as we are having huge condensation issues. I'm running a dehumififier about 8-20 hours a day, along with AC. Not sure what to do at this point other than dehumidify all day long. Not sure if fiberglass bats would have been better but i'm just frustrated. Edit; spelling Recently built on a slab? Slab new? Concrete will give off moisture for quite some time. When I built my house I had to run the dehumidifier in the basement all the time for a full summer and fall. That winter I ran the dehumidifier a bit but also ran a wood stove and that helped dry it out some more. The next year it was better and even better the following year. Still run a dehumidifier in the spring and fall but it doesn’t run a lot. Where are you getting the condensation at? |
"It behooves every man to remember that the work of the critic is of altogether secondary importance, and that, in the end, progress is accomplished by the man who does things."
Theodore Roosevelt
Theodore Roosevelt
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Originally Posted By ColtRifle: Recently built on a slab? Slab new? Concrete will give off moisture for quite some time. When I built my house I had to run the dehumidifier in the basement all the time for a full summer and fall. That winter I ran the dehumidifier a bit but also ran a wood stove and that helped dry it out some more. The next year it was better and even better the following year. Still run a dehumidifier in the spring and fall but it doesn’t run a lot. Where are you getting the condensation at? Originally Posted By ColtRifle: Originally Posted By mouthpiece: Built a 45x90 stick build covered in metal(barndo, but not a true barn build) 1/2 shop 1/2 house, 35x40 loft/attic storage finished and floored. 2x4 walls filled and 2x6 ceiling purlins filled with open cell, shaved to the stud. Not real excited about it as we are having huge condensation issues. I'm running a dehumififier about 8-20 hours a day, along with AC. Not sure what to do at this point other than dehumidify all day long. Not sure if fiberglass bats would have been better but i'm just frustrated. Edit; spelling Recently built on a slab? Slab new? Concrete will give off moisture for quite some time. When I built my house I had to run the dehumidifier in the basement all the time for a full summer and fall. That winter I ran the dehumidifier a bit but also ran a wood stove and that helped dry it out some more. The next year it was better and even better the following year. Still run a dehumidifier in the spring and fall but it doesn’t run a lot. Where are you getting the condensation at? Yes new slab poured in late 2025. Condensation on the slab. |
AcidGambit, I’ve always wanted to milk a lactating chick... Like make her get on her knees, milk her tits, and make her moooo.
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Originally Posted By mouthpiece: Yes new slab poured in late 2025. Condensation on the slab. Any insulation under the slab? Any plastic vapor barrier under the slab? Do you have gutters AND are they routed to move the water away from the foundation? |
"It behooves every man to remember that the work of the critic is of altogether secondary importance, and that, in the end, progress is accomplished by the man who does things."
Theodore Roosevelt
Theodore Roosevelt
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Earth? Never heard of insulating under a slab. Yes Tyvek on the walls before metal No plastic vapor barrier under slab. I think builder should have used it and I suspect that is part of the problem. No gutters, yet. May also be part of the problem Build is raised 3' above surrounding land . |
AcidGambit, I’ve always wanted to milk a lactating chick... Like make her get on her knees, milk her tits, and make her moooo.
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Originally Posted By mouthpiece: Earth? Never heard of insulating under a slab. Yes Tyvek on the walls before metal No plastic vapor barrier under slab. I think builder should have used it and I suspect that is part of the problem. No gutters, yet. May also be part of the problem Build is raised 3' above surrounding land . Insulating under slabs is more common in cold climates but it would probably help reduce concrete sweating in the spring in your case as well when the soil and concrete is cold but the air is humid. It ensures the slab stays warmer than the soil. Plastic under the slab would help somewhat to reduce moisture migrating from the soil through the concrete. But, it is what it is. I think your first cause is the new concrete giving off moisture. Nothing you can do about that other than time and dehumidification. Luckily, it’ll get better with time. Run your dehumidifiers full time all summer. Keep the humidity level below 55%. Run them in the winter if humidity gets above 55%. It’ll dry out eventually. Definitely get gutters ASAP. A roof can produce 1/2 gallon of water per square foot of roof area per inch of rain. Typically thousands of gallons per inch of rain. Remember your roof is pitched so you have even more square footage of roof than you have house square footage. Dumping all that water at your foundation will encourage at least some of it to soak under the foundation and then wick up through the concrete…..especially without a vapor barrier under the concrete. Gutters and down spouts are great but they have to drain away from the house. Doesn’t do you any good to run your water into gutters and then dump all that water at your foundation! I ran some 4 inch pvc under ground and that carries the water away from my foundation. I don’t think your insulation has any affect on your moisture levels inside the house. |
"It behooves every man to remember that the work of the critic is of altogether secondary importance, and that, in the end, progress is accomplished by the man who does things."
Theodore Roosevelt
Theodore Roosevelt