In Arkansas, the hard part of insulating a steel container is moisture as much as temperature. A good plan slows heat through the steel and keeps humid air away from any surface cold enough to collect water.
Air carries water vapor. When that air touches a surface colder than its dew point, some of the vapor turns into liquid water on the surface. Steel changes temperature quickly, so the walls and roof of a container can fall below the dew point of the air inside on a clear night. An air conditioner can do the same thing to an interior surface in summer.
The water collects where it is hard to see: behind stacked boxes, under the roof panels or inside a wall cavity. Over time it stains contents, feeds mold and rusts the steel from the inside.
The energy code assigns every county a climate zone. In the U.S. Department of Energy's guide to climate regions by county, 63 Arkansas counties fall in Climate Zone 3A and twelve northern counties fall in 4A: Baxter, Benton, Boone, Carroll, Fulton, Izard, Madison, Marion, Newton, Searcy, Stone and Washington. The letter A marks a moist climate. Pulaski, Faulkner and Craighead counties, which hold Little Rock, Conway and Jonesboro, are all in 3A.
The Arkansas Energy Office's building energy codes page says the state uses the 2014 Arkansas Energy Code for commercial and residential construction, based on the 2009 International Energy Conservation Code, and that an update is being drafted. Little Rock adopts the 2014 Arkansas Energy Code in Section 8-2 of its code, and the code lists published by Conway and Jonesboro name it too.
For a container that will be heated or cooled for people, ask the building department that reviews the plans which insulation values apply. They depend on the climate zone, the type of assembly and how the space will be used, so get them before you buy materials. Our Arkansas permit guide explains which office governs a parcel.
In an Arkansas summer the roof takes the most direct sun, and a steel roof passes that heat to the space below. Three measures work together:
Build any carport or roof frame after delivery, or keep the delivery path clear while it goes up, because a frame over the drop spot can block the height the truck needs to unload.
Closed-cell spray foam applied directly to the corrugated steel is a common choice for containers. It insulates, and it also keeps air from reaching the steel, which stops condensation from forming behind it. Rigid foam boards can work when every seam and edge is sealed, because any gap lets humid air reach the steel behind the board.
Fiberglass or mineral wool batts in a framed wall need an air-tight layer and a moisture plan that suits a humid climate. Batts pressed against bare steel let damp air reach the cold surface and hide the water that forms there. Before the wall is closed, ask the building department, or your designer if you have one, where the air barrier and any vapor control belong.
Every method takes inches from the inside of the box. The 40ft high cube is one foot taller than a standard 40ft, so it keeps more headroom after the ceiling and floor are finished. The 40ft high cube page lists its dimensions.
A container floor is plywood laid on steel cross members, and the underside of the box sits close to the ground. In a humid climate the floor needs protection from ground moisture as much as from heat. Set the container on firm, drained supports so air can move underneath, and insulate under the floor if the space will be conditioned.
Drainage also protects the level of the box. The Arkansas Geological Survey notes that expansive clays in Arkansas shrink and swell with their moisture content. Corners that settle unevenly rack the frame, and racked doors stop sealing.
A container that will not be heated or cooled usually needs moisture control rather than insulation:
Paint, adhesives, aerosol cans, batteries and electronics are better kept somewhere with temperature control during an Arkansas summer.
The 4A counties in the Ozarks have colder winters than the rest of the state. A heated container there needs the same air-tight approach in reverse: warm, moist indoor air must not reach the cold steel. Foundations change too. Rogers and Mountain Home both list an 18 inch frost line depth in their published design criteria, so ask the building department that will issue your permit for its figure before footings are dug.
Whether the insulation goes in after the container is set or a modified container is insulated and finished before it ships, the container has to reach the site. Container One requires 110 feet of straight, unobstructed space for a 20ft container and 130 feet for a 40ft, at least 15 feet of height to drive, 22 feet of height along the unloading path and 10 feet of width.
For a quote, send the delivery address and how you plan to use the container through our quote form. The container homes guide covers foundations, earthquakes and zoning for a project people will live in.
This guide is general information, not engineering or code advice. Confirm insulation, energy code and foundation requirements with the building department that reviews your project.