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Community and Q&A

Polyiso rigid insulation on cargo container

jacksamcharlie | Posted in Energy Efficiency and Durability on

My plan is to use a 3″ thermax board on the outside of my over seas cargo containers for a living space. My question is should this keep condensation from building inside the containers or am I still going to run into that problem? How much difference would a spray foam make compared to rigid board? Pros cons either way?

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  1. GBA Editor
    Martin Holladay | | #1

    Jack, Sam, Charlie,
    I assume that your plan includes siding and roofing.

    You'll get condensation whenever warm, humid air can contact the cold steel. In the summer, you have to prevent outdoor air from sneaking between the seams of your polyiso. In the winter, you have to have a heating system that keeps the interior of your container warm (and therefore above the dew point).

    There are several issues to consider. One is how you will insulate your foundation. Remember that your foundation (floor) insulation needs to be continuous with your wall and roof insulation.

    The second issue is how you will make sure that the seams of your polyiso will be airtight. Presumably you will use canned spray foam in combination with a high quality tape at the seams.

    The third issue is: once you have built an insulated foundation, and created a structure to hold up your siding and roofing, will this new building be any less expensive than starting from scratch (without a steel container in the middle of your complicated assembly)?

  2. GBA Editor
    Martin Holladay | | #2

    The idea of converting a steel shipping container into a home crops up regularly on GBA. For several years, we've consistently advised readers that these projects make no sense.

    Most of the arguments against the use of steel shipping containers as homes can be found in this GBA article: What’s Wrong With Shipping Container Housing? Everything.

  3. JC72 | | #3

    IMO other than selling the container to a trucking company the only way to make this cracker box work it to build a shell within the shell of the container and insulate the space in between with ccSPF. (Think of how a submarine is built) Run your wiring/plumbing/ventilation,support beams for the interior framing and then spray the interior side of the container with ccSPF to whatever depth you're willing to give up with regards to interior space.

    It won't be perfect but living in tin box was never going to be perfect anyways. Realistic expectations are a must.

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