Container Insulation.
A steel container has no cavity, no absorbency and a corrugated profile that no batt fits. It also runs below the dew point of its own interior air for much of a Central Alberta year, which is why the water appears on the ceiling.
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Container sweating is a surface temperature problem. Any insulation that lets interior air reach the steel behind it will move the condensation rather than stop it — which is why an adhered, air-impermeable layer is the assembly that works here.
Where a container is being converted into an occupied building rather than used for storage, the exemptions stop applying and the assembly has real code targets — the Zone 7A figures are set out here along with the tables they come from.
What Makes a Steel Box Different.
Every property that matters here is a consequence of the substrate being non-absorbent, highly conductive, corrugated and completely airtight except where somebody cut a hole in it.
- An air-impermeable layer bonded directly to the steel, so interior air never reaches the cold panel. Closed-cell foam clears the code's air barrier material threshold at roughly 25 mm, with published products testing around 0.002 L/(s·m²) at that thickness.
- Vapour control from the same layer at 50 mm, the thickness at which CAN/ULC-S705.1 sets its 60 ng/(Pa·s·m²) pass/fail — relevant because steel is a perfect vapour barrier on the cold side.
- The corrugation followed rather than bridged, which a sprayed material does and a rigid board or batt does not without a framed cavity behind it.
- Published adhesion to steel is not something we will invent a figure for; what is published is that closed-cell foam bonds hard to sound, clean, dry substrates and that surface preparation governs the result.
- Substrate conditions checked before spraying: clean, dry, frost-free, at least 3 to 5 °C above the dew point, ambient humidity under 80 percent. On bare steel outdoors in shoulder season that usually means enclosure and heat.
- Service temperature limits respected, since closed-cell foam is rated from -60 to +80 °C and a dark container in July sun is a genuinely hot substrate — one manufacturer publishes a separate high-temperature vapour permeance value measured at a 40 °C substrate.
- Lift thickness held to the CAN/ULC-S705.2 baseline of 50 mm per pass with cooling between passes, which matters more in a small enclosed steel volume than almost anywhere else.
- Thermal barrier decided by use: foam left exposed inside a container people occupy is not in a concealed space, and Article 9.10.17.10's covering requirements apply.
Preparing a Container.
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Establish the use
Unheated storage, a heated shop, or a conversion to an occupied building. The third is a building code question with real targets attached; the first two are condensation and comfort questions.
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Prepare the steel
Clean, sound, dry and frost-free. Adhesion to a contaminated or damp panel is where container jobs fail, and the panel is the entire structure here — there is no framing to fall back on.
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Control the environment while spraying
A container is a small volume with high thermal mass in the panel. Bringing the substrate into the product's published range and holding it above the dew point is the difference between a bonded layer and a delaminating one.
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Ventilate and re-occupy on the published time
Time to occupancy is 25 hours for essentially every current Canadian closed-cell product, with mechanical ventilation of at least 0.3 air changes per hour during and after installation. In an enclosed steel box that ventilation requirement is not a formality.
Frequently Asked Questions About Shipping Container Insulation
Why does the inside of my container get wet?
Because the steel panel drops below the dew point of the air inside it. Steel has effectively no thermal resistance and no absorptive capacity, so it tracks outdoor temperature almost exactly, and any moisture in the interior air — from stored goods, from the ground, from people, from a heater — condenses on the first cold surface it reaches. The insulation question is therefore about keeping interior air off the panel and keeping the interior surface above the dew point, not about reaching an R-value target.Can batts or rigid board be used in a container instead?
They can be installed, but they solve a different problem. A batt is air-permeable, so interior air still reaches the steel behind it and condenses there — out of sight, against the panel, rather than visibly on the ceiling. Rigid board needs a framed cavity, which loses interior width in a space that has very little to give, and it leaves a gap at every corrugation unless the framing is furred out past the profile. An adhered, air-impermeable layer sprayed directly onto the steel is the assembly that addresses the actual mechanism.How thick should container foam be?
It depends what the container is for. For condensation control the requirement is continuity and air impermeability, which closed-cell foam achieves at around 25 mm. If the foam is also to be the vapour barrier, 50 mm is the code-anchored figure. If the container is being converted into occupied, heated space, then the Zone 7A effective RSI targets apply to the assembly like any other building, and the thickness follows from those.Does foam in a container need to be covered?
If people occupy the space, yes. Article 9.10.17.10 requires foamed plastics forming part of a wall or ceiling assembly to be protected from adjacent space by an interior finish, by sheet metal at least 0.38 mm thick with a melting point of at least 650 °C where there is no Group C major occupancy, or by a listed thermal barrier. The concealed-space carve-out covers foam inside a closed assembly, and a container with foam sprayed on the inside face of the panel is not that.Can a container be sprayed outdoors in an Alberta winter?
Only with enclosure and heat, and that is engineering rather than upselling. Winter-grade closed-cell products publish substrate ranges of roughly -10 to 10 °C, with the coldest published Super Winter grade at -20 to 0 °C. Red Deer's January design temperatures are -32 °C at the 2.5 percent level and -35 °C at 1 percent, which sits below every published winter grade. The steel also has to be frost-free and at least 3 to 5 °C above the dew point, which on a cold panel being warmed is exactly the condition that produces condensation if it is rushed.