Insulation for a shipping container

Internal or external insulation ?

log burning safe
  5 Aug, 2015

Should you insulate on the inside or the outside of a shipping container?, or even both. There are so many products available but which one is right for your situation?. Spray foam has a lot of good publicity but you have to have your container completely fabricated and empty prior to spraying. A more conventional frame and insulation will take up more space inside.....

Having started to build a container house, I was consumed by the different ideas for ways to insulate it. Here are some of the concepts I thought of:

You could buy an insulated container, the type used for transporting chilled or frozen goods. You could spray foam insulation inside, You could install a wooden frame and fit conventional insulation batts, You could skip the insulation and go naked (bare steel), You could spray space age insulation products on the exterior, You could externally insulate with a cladding.

My early attempts to embrace the "steel theme" left us very cold. We hung temporary insulation from the top of the walls. We found that silver foil bubble wrap was affective at reducing the cold, and a covering of fabric improved the appearance and made it less like sitting in a space vehicle. I eventually installed a wooden frame, and put a reflective builders wrap, insulation batts and finally a covering of 12mm plywood. This made us a lot cosier.

Being in Australia, heat from the summer sun was our biggest challenge. The most effective solution was a sunroof over the entire container. In an ideal world I would have had the container sunroof extend 2m beyond the perimeter of the container roof. My desire to keep the containers portable meant I kept the sunroof to a minimum overhang. I use shadecloth to extend the shade without requiring significant structure.

My containers are painted with an additive called "Thermilate" which claims to make a difference. My experience was that colour selection outweighed the additive, and a reflective colour is an essential step in regulating the temperature in summer.

I have seen a container clad in a Cedar wooden shingle or board. These are beautiful, but unsuitable for me in my situation. Timber cladding in the bush is a fire risk, it would also compromise the external dimensions. When you make the container wider than its original size it is no longer legal to be carried without extra travel precautions and oversize notices and signs.

I rejected spray on foam as I felt I would have to have the container fabrication completed before the spray was applied. I was also concerned I would not be able to weld the container or use cutting tools that generated heat for fear of starting a fire in the foam. This arguement was the motivator to reject a pre insulated container. Pre insulated containers are very expensive and hard to come by.

I have seen pictures of a simple container house clad externally with a cement board. It looked simple and effective.

I document my insulation evolution in the ebooks, and also cover the costs for those with a deeper interest.