basic container design – insulation

Since mankind crawled out of the caves and began building shelters for ourselves we’ve been obsessed with maintaining a comfortable interior temperature. This is especially true when working with a steel shipping container…after all, IT’S STEEL! If left in the heat, unprotected, interior temperatures will rise higher than the inside of your car on a hot day – and we all know what it feels like to sit on hot leather seats…OUCH.

So how do we insulate a container, not just to maintain interior comfort but also to ensure that our finished structure will remain safe? (note – heat greatly effects the physical properties of every product used in a home or building) There are various types of insulation we can use based on insulating characteristics and cost. Common types of insulation are:

Batt or Roll Insulation: Most common. Found at any hardware store. It’s “the pink stuff”. About R-3 per inch. Cheap and easily installed. In a typical 2×6 stud wall you’ll get about R-18…at least so the label tells you. You’re really getting less than that because it’s nearly impossible to install perfectly, which means you get all kinds of voids and crimples, etc. that affect the R-Value.

Loose Fill or Blown Insulation: Also found at most hardware stores and is made from shredded blue jeans or paper or cellulose. About R-4 per inch. Also cheap, but requires renting equipment to install and can be difficult to fill stud cavities in existing buildings. It’s great for attics and other large spaces.

Rigid Board Insulation: Typically Polystyrene or Polyisocyanurate (plastic). Comes in sheets that are easily cut to size. About R-4 to R-7 per inch. Sort of cheap and easily installed. Can be cut to size and placed in stud cavity. A typical 2×4 wall will give you up to R-21, but again this is affected by voids and joints in the boards.

Spray Applied Insulation: Either open cell or closed cell. Open cell will absorb moisture, so it should not be used in moist climates. Closed cell creates an air tight barrier and is expensive. Both require skilled installers. Most bang for your buck in terms of performance. About R-4 to R-6 per inch (though some say it can be as much as R-10 or R-12 per inch). When insulating containers, I find it best to insulate one of three ways: exterior, interior or both interior and exterior. In extreme climates, warm or cold, it’s best to insulate both interior and exterior to achieve the maximum R-Value without sacrificing too much square footage while still protecting the container and providing necessary cavity space for electrical and plumbing.

Poured or Injected Insulation: Similar to spray applied. Installation is either through a series of holes cut into existing walls or through the sill plate at the top of the wall. Great for renovations and retrofits. Expensive and requires skilled installers. R-values similar to SPF – about R-6 per inch of thickness.

Radiant Barriers: This is a new technology and has not been well tested over time. You may have seen things like ceramic coatings featured by Bob Vila and others touting their sometimes miraculous benefits. I’m optimistic for the technology, but will reserve final judgement for when the product has been time tested and proven. The basic principle is in the name – it creates a barrier that radiates heat energy away from the surface without allowing it pass to the interior.

Any of these insulating materials are suitable for use in a shipping container home. Remember that the container itself is just a building block, one component of the building envelope, no different than wood or metal studs and sheathing. So just like with any other material, it’s important to figure out your cost/benefit scenario early. Options are wide spread and it is simply finding a balance between what you want your home to look like, how you want it to function and how much money you want to spend. Consulting trained architects and designers early on in your project will save you lots of time and money down the road as well.