The steel a shipping container is made from is called corten, or more properly weathering steel. It forms a stable layer of surface rust that then protects the steel underneath from further corrosion. Left alone in a temperate climate, corten will outlast almost any other outdoor structure at its price.
Left in the wrong conditions, corten fails faster than most people expect. The difference between a 30-year container and a 10-year container is not the steel. It is what happens around it.
How long a container actually lasts
The industry rule of thumb is that a shipping container in active shipping service lasts 10 to 12 years before it is retired. That is the point at which the CSC inspections start failing often enough that keeping it in service is not economic.
Once retired from shipping and used for static storage, the same box typically lasts another 15 to 25 years without significant repair, provided it is kept out of standing water and rust is dealt with when it appears.
A container in a dry inland climate — Arizona, Nevada, most of Texas — can last well beyond that. Containers manufactured in the 1990s that were retired around 2005 are still in use as storage today, thirty years after they left the factory, in reasonable condition.
A container in a coastal climate is a different story. Salt air accelerates corrosion, and a container on the Gulf or Atlantic coast will typically lose 5 to 10 years off that timeline. In Florida, we see storage containers needing panel repairs after 12 to 15 years that would still look sound after 20 in Arizona.
What kills a container early
Three things are responsible for almost every premature failure we see.
Standing water
Corten resists corrosion in cycles of wet and dry. It corrodes fast when it stays wet. A container sitting in a low spot that pools after rain, or with a badly-designed roof drain overflow above it, will rust from the outside in at the base and from the top down where water sits.
The fix is to sit the container off the ground on four sleepers or corner blocks. Three or four inches of clearance is enough, and any nearby drainage should point away from the base. See our site preparation guide for how we usually set them up.
Roof damage that is not repaired
A shipping container roof is not designed to be walked on. Dents from tree branches, dropped tools, or someone standing on it collect water and start rust from the inside of the dent outwards. Small dents fixed within a year of appearing are a repaint job. The same dent left five years is a panel replacement.
Once a year, get up on a ladder (not on the container) and look at the roof. Anywhere the paint is broken, a rust patch is starting to form, or a dent is pooling water, spot-clean and touch up. It is ten minutes of work.
Doors that do not close properly
Sounds minor. It is not. A door that does not seal lets rain in, and rain inside a sealed steel box condenses on the walls, runs down, and starts rust patches in places you cannot see until they have grown. Doors that do not close usually mean the container has twisted, most often because it is sat on uneven ground.
Fix by levelling the corner supports. A container that sits square usually has doors that close square. If levelling does not fix it, the container itself is out of true and the hinges need adjustment by someone who knows what they are doing.
Maintenance that actually matters
Almost nothing. A shipping container is designed to sit on a ship's deck through storms for a decade, and it does not need looking after in the way a wood shed does.
The three things worth doing:
- Annual roof check. Ladder up, walk around, look. Ten minutes.
- Annual seal check. Open and close the doors. If the rubber seal is cracked or the doors do not clamp firmly, either replace the seal ($80 to $150 for a full door set) or ask us about door adjustment.
- Spot-paint rust as it appears. A tin of matching paint, a wire brush, ten minutes a year. Marine-grade rust-inhibiting paint like Rust-Oleum Original works fine.
That is it. Painting the whole container is a job every 8 to 10 years if you want it to look tidy, more often if it is near the coast. It is cosmetic on a corten container. The steel does not need the paint the way ordinary steel would.
Signs your container needs attention
Three things worth acting on quickly.
- Rust on the underside of the roof panels, visible from inside. That is water sitting on top for long enough to eat through the paint. Fix the drainage or the roof dent that is holding water.
- Rust running down the corners inside. Almost always condensation from poor ventilation. Add a couple of vents or a small extractor. The box should not be airtight if it is in an area with big day-to-night temperature swings.
- Any hole through the wall or roof. Fix within days, not weeks. A small patch or weld is quick. Leaving it lets water in and rust out from the inside.
When to retire a container
The point where repair costs more than replacement. That is usually when there is structural rust in the corner castings (the eight steel corners), or when the floor has soft spots across a large area. Panel rust is repairable. Corner-casting rust is a structural problem, and the container cannot safely be moved once it is advanced.
A container reaching that point after 25 years of static storage has done what it was supposed to. Depending on where you are, we sometimes buy back older containers for scrap value. Get in touch if you have one to shift.
Common questions
Do I need to paint a new container?
No. New and one-trip containers are factory-painted with a marine-grade paint system that will last 8 to 10 years in inland conditions. Repaint when the paint starts to lift, not before.
Can I insulate a container without accelerating rust?
Yes, if you leave a small ventilation gap between the insulation and the steel, or if you use closed-cell spray foam directly onto the walls. What causes trouble is fitting insulation with a still air gap and no ventilation. Condensation forms behind the insulation and cannot escape.
Are older containers better made?
Marginally, on average. Containers built before about 2005 tend to have thicker corner castings and slightly heavier corrugation. Containers built since are made to the same ISO standard but with material tolerances that have crept lighter. In practice the difference is small and rarely a reason to choose one over the other.
What about container homes: do they last?
Yes, if the modifications are done properly. Cutting large openings without reinforcement weakens the box and creates places for water to enter around the frame. A container home built with proper header reinforcement, sealed penetrations and a real roof over the top will last as long as any purpose-built small building.
Before you buy
If you are buying a used container, two things are worth checking specifically for lifespan.
- Look at the corner castings from underneath. If they have heavy rust, the container may not have many years left even if the rest looks fine.
- Look inside for water stains high on the walls. Water stains near the roof mean past leaks that may not be fully fixed.
Our cargo-worthy and wind-and-watertight containers are inspected against both. If you are not sure what condition grade you are looking at, our grade guide covers what each label promises.
Questions on a specific container or site? Get in touch and we will walk you through it.