May 15, 2010 - The idea of being inside of a large metal box in the heat of a Houston, Texas summer is a bit scary. The insulation decision is a big one because of its long-term impact on the comfort and success of the Creative Co-Op. The challenge is to get the building property insulated from the elements, keep the occupants comfortable, and do it in a cost-effective way. Part of the fun of building a non-conventional structure is doing the research to find out what others have done and their experience. The internet is excellent for this kind of research. Unfortunately, for cargo container insulation there is not one single source of great information, but I was able to glean some information from blogs, online forums, and web sites.
Below I will share my findings with you, followed by my ideas for an insulation system and some comments from our architects.
- For insulation and a thermal block, use styrofoam attached with adhesive to the walls. You can incorporate a fiberglass mesh-like stucco system and then paint... I have incorporated this technique in building containers. Affixing styrofoam insulation with adhesive has been in my mind for quite some time now, and I'm glad to hear that it works. I have never seen the need to build another extensive wood or steel stud structure inside the steel walls of a container. I saw at a green festival a few years ago a sample cross section of a certain type of foam/concrete building system and, if I recall correctly, they had glued 1/2" drywall to the foam using expanding polyurethane foam. I think the guy at the booth said that is indeed how they did it in the actual buildings they constructed. I would think paneling could work also (something stylish/durable of course, bamboo?, etc...)
- Just a note on my experience with insulation - I've had a 20' container in Alaska (humid Southeast) for some 15 years which I use for secure storage in a remote location. I used "Liquid Nails" to glue 1.5 inch rigid, closed cell, foil-faced urethane insulation on the inside of the container. Adding a couple of portholes I had laying around did little to stem the condensation on the inside. I was amazed to see very little rust considering the time and the amount of water present (corten steel). Last year the insulation on the ceiling fell off, but the walls are still covered. I suspect that a proper vapor barrier and a managed air handling system used in the more modern super insulated homes could handle the problem. This was the reply below it:
- Be careful here - the steel shell of the container is a de facto vapor barrier. If you put another one on the inside then any moisture that finds its way in there is going to be trapped. You have to see what is convention for this region - vapor barrier on inside or outside and decide what to do.
- Insulation, of course, will depend on your location (Antartic vs tropics). Always be wary of condensation forming on the inside of the container. a) Use furring strips: I have seen furring strips in combination with 4 x 8 sections of plywood. You can place insulation board with the appropriate R-value on one side, then use furring strips to adhere the insulated side of the plywood to the container wall. b) Use spray foam insulation: This will require professional equipment and a well ventilated area but if done properly can provide a secure bond between the steel wall and the foam. c) Use Kemlite: I believe Kemlite is the insulating material used in a lot of insulated/refrigerated containers.
- Designs that work – insulation for hot humid climates: http://www.buildingscience.com/documents/designs-that-work/information-sheet-houston-profile/?topic=/doctypes/designs-that-work - this link shows a cross section for a typical structure in the south.
- If you will not be raising the humidity level significantly, you should not have condensations problems on the inside of the steel. But if any water gets inside those walls by any source, you want them to be able to dry out to the inside, so do not use plastic. A cold dry or mixed dry climate would normally call for the vapor barrier to be to the inside. When designing with containers, this can be accomplished by insulating to the outside of the steel walls. But again, a residence would have a lot more mositure due to the nature of the use (showers, cooking, clothes drying, etc.). Insulating to the inside should work fine in a shop.
- As for insulation... I hear that Polyurethane Spray Foam works best on the interior. You could build an interior metal stud wall and have several inches of foam. I believe they say that 1″ of foam = about an R7-R8 plus it works well for a moisture barrier I am told. Others mention that, in addition to spray foam, a ceramic insulative paint additive could be used on the exterior to augment the insulation values. (about equivalent of R7 per double coat)
- I have read in various places about insulating containers that there is a danger of condensation build up if you insulate the inside of the containers with batt-type insulation, without insulating the outside. This can cause numerous problems. It is better to insulate either the inside or outside with spray insulation which can give you a high degree of insulation value. Obviously, you would then have to clad the side you have insulated for aesthetics (unless you like the look of spray foam insulation).
- I have read articles on a couple website about ISBU insulation, and they seem to indicate that PU Spray foam on the inside and ceramic insulation on the exterior seems to work best.
- George Runkle of Runkle Consulting, Inc. has some great ideas on his blog The Castle. His comments on insulation are: "In the (container) house in Atlanta, and also in the buildings in Uzbekistan, the walls were furred out and insulation placed between the studs. In the Atlanta house, it was blown in insulation, in Uzbekistan it was fiberglass batts.”
Based on this information, the insulation system I came up with was:
- Exterior Walls – On the outside of the building we clean, prime and spray on two coats of a water-based ceramic paint, like Supertherm or ThermaCote.
- Interior Walls – We use a closed-cell water-based foam made from “sugar beets” which will not outgas. I am concerned with cellulose that condensation could trap moisture in the walls. Liquid nails might be a less expensive alternative than double sided tape to hold the metal studs to the walls. The walls will be covered with sheetrock or wood paneling.
- Ceilings – 1st Floor - Nothing. 2nd floor - On the tops of the containers we can use traditional fiberglass insulation, and a thermal barrier foil on top of that.
- Roof (attic crawl space) - There is an air space between the top of the containers and the roof. The roof will be Rpanel affixed to either metal or wood rafters. The cavity space between the rafters will be filled with fiberglass bats typically used for metal building insulation.
Our architects (Shapespace) made the following suggestion:
"We feel confident that based on climate, cost, and green factors, cellulose insulation with 1 x 2 furring strips (wood or metal) will out-perform alternative insulation options. With cellulose, a proper air sealing component along with spraying the exterior will surely prevent any moisture or vapor. We can then finish with either drywall or paneling as mentioned. Closed cell insulation will require more material, resulting in higher costs, and is not the most 'green' product either. Having said this, I do know the product to perform well. "
Based on their comments I started doing research on cellulose insulation and I was suprised to find some very amazing things about it. I will tell you more about my findings in Part II of this blog posting.
Posted by Vic Cherubini on May 18, 2010
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