With steel roofing for barndominiums, shouses and post frame (pole) buildings comes condensation.
When atmospheric conditions (in this case temperature and humidity) reach dew point, air’s vapor is able to condense to objects colder than surrounding air temperature. Once vapor condensing occurs, droplets are formed on cool surfaces. This is partly why warming a vehicle’s windshield with a defroster can prevent glass ‘fogging’.
When a building’s interior air meets these conditions, air vapor will condense to cool surfaces. Steel roofing cooled by exterior air temperature often provides this surface. Droplets formed will combine as they contact one another, continuing to do so until they are too large to be supported by surface tension. At this point, dripping will occur, essentially raining on your structure’s contents.
Commonly (when addressed at all during construction) solutions to this problem have often involved creating a thermal break. A thermal break reduces contact between a structure’s warm interior air and cooler metal roofing, thereby reducing or eliminating overall condensation. Installing a reflective radiant barrier, often termed Vapor Barrier, involves laying rolls of faced ‘bubble wrap’ across your building’s purlins prior to roof steel installation. Ideal weather conditions are required for this as even a slight wind can make this a challenging or altogether impossible task. This can cause jobsite delays and may bring progress to a halt while a structure remains unprotected to weather. Even when ideal weather conditions are present, installing a reflective radiant barrier can be a very dangerous task, requiring builders to expose themselves to awkward material handling on a building’s bare roof framing. These risks and delays often generate additional costs for both owners and builders, but have often been necessary with reflective radiant barrier being the only relatively affordable option to prevent interior dripping.
New materials and production methods offer a better solution. Utilizing polyester fabric’s absorption characteristics and their integral application during roll-forming, most better quality steel roofing roll formers offer a ready-to-install roofing panel with integral drip-protection. I.C.C. is a pre-applied solution reaching jobsites ready for immediate installation. Delays and increased jobsite workload caused by problems associated with radiant reflective barriers are eliminated by this product. Also, due to this solution’s simplicity, panels with I.C.C. install using the same methods, fasteners and time similar panel-only installations require. No changes to installation processes are necessary, with an exception of time and effort saved.
It works because this polyester membrane simply retains liquid until atmospheric conditions allow it to be re-evaporated. This is because polyester is hydrophilic, meaning water is attracted to it. It acts as a wick, harmlessly absorbing condensing vapor. Rather than preventing condensation, it provides an absorbent layer to detain condensing vapor until it can re-evaporate as temperatures increase and humidity decreases.
“I am currently re-siding/re-roofing an existing pole building in order to match the exterior of the building I recently purchased from you. This building is roughly 32 x34 and the roof purlins are 2×6 on end roughly every 2 feet. I’m using Fabral’s grand rib 3 29ga for the roof and it will have fully vented soffit overhangs and a vented ridge cap. I am trying to figure out what I’m going to do for at least a vapor barrier under the roof steel, I see you seem to recommend foil faced bubble insulation but that is not very common in my area. I am seeing a lot of people using lamtec wmp-vrr (fiberglass insulation with a poly backing) 3″ thick and I believe they lay these wide rolls on top of the purlins and then place the metal roofing on top of that then screw down the roofing compressing the fiberglass insulation between the metal roofing and the purlins. Have you seen this style of insulating before? Do you think it is an acceptable way of doing it? I see as killing two birds with one stone. I may be insulating this shop in the future so if I do then the roof is already insulated plus I believe it acts as a vapor barrier which is the main reason to do it as I don’t want any condensation dripping down on the inside of the shop. I live in the Seattle area if that helps to know what my climate is like. Thanks in advance for your input.” 
Commonly (when addressed at all during construction) solutions to this problem have often involved creating a thermal break. A thermal break reduces contact between a structure’s warm interior air and cooler metal roofing, thereby reducing or eliminating overall condensation. Installing a reflective radiant barrier, often termed Vapor Barrier, involves laying rolls of faced ‘bubble wrap’ across your building’s purlins prior to roof steel installation. Ideal weather conditions are required for this as even a slight wind can make this a challenging or altogether impossible task. This can cause jobsite delays and may bring progress to a halt while a structure remains unprotected to weather. Even when ideal weather conditions are present, installing a reflective radiant barrier can be a very dangerous task, requiring builders to expose themselves to awkward material handling on a building’s bare roof framing. These risks and delays often generate additional costs for both owners and builders, but have often been necessary with reflective radiant barrier being the only relatively affordable option to prevent interior dripping. 
