Short answer: a cargo worthy (CW) container is certified for international shipping, while a wind and watertight (WWT) container is weatherproof but not certified — better suited for storage. Everything else is detail. Important detail, though, so read on.
Key Takeaways:
- CW containers hold a valid CSC plate, confirmed by a licensed marine surveyor — cleared for international transport
- WWT containers are sealed against wind and water but carry no CSC certification — ideal for domestic storage purposes
- Both grades will have rust, dings and dents — appearance alone won't tell you which is which
- CW containers typically have better door seals and floor condition than WWT units
- WWT is the more cost-effective and widely available option for on-site storage needs
- A WWT container can be repaired and recertified as cargo worthy if your needs change down the line
What Is a Cargo Worthy (CW) Shipping Container?
A cargo worthy container is a used shipping container that’s been inspected by a licensed marine surveyor and certified as structurally sound for international shipping.
To earn the CW grade, the container must pass the requirements of the CSC — the International Convention for Safe Containers. Pass the inspection, get the valid CSC plate. Simple enough in theory, though the inspection itself is rigorous.
These containers are built for punishment. We’re talking stacked up to 21 units high on a cargo vessel, loaded with up to 40,000 lbs of goods, and exposed to ocean weather. Structural integrity isn’t optional here — it’s the whole point. Popular sizes like 40ft shipping containers are commonly sourced as CW units for exactly this kind of heavy-duty international freight transport.
Worth knowing: CW containers are graded just below the IICL standard — the benchmark set by the Institute of International Container Lessors, which represents the highest quality tier in used containers. Most CW units are 7–15 years old.
What Does Wind and Watertight (WWT) Actually Mean?
Exactly what it sounds like — no wind, no water gets in. No holes, no leaks, no light sneaking through the seams.
What a WWT shipping container doesn’t have is CSC certification. That means it can’t be loaded onto a vessel for international shipping. It’s been retired from active freight transport — typically sold off by container lessors once the unit’s been fully depreciated — and it ends up on the second-hand market, often at a noticeably lower price. If you want a clearer picture of what to budget, our guide on how much a shipping container costs in the UK breaks it all down by grade and size.
Expect surface rust, faded paint, dings and dents, and possibly some welded patch repairs. Most WWT containers are 10–15 years old. The yard checks them over before sale — not a formal governing body — to confirm they meet the wind and watertight standard.
For domestic storage purposes, a WWT container is a genuinely solid option. Weatherproof, rodent-proof, secure. Options like 20 foot shipping containers for sale in WWT condition are among the most popular choices for businesses needing reliable on-site storage without paying a premium for export certification. Most buyers don’t need anything more than that.
They Look Nearly Identical — So Where's the Actual Difference?
The real difference tends to show up in three places:
- Door seals - CW containers typically have intact, functional gaskets; WWT units may have compromised seals
- Floor condition - cargo worthy floors tend to be in better shape, with fewer patched sections
- Structural confirmation - C has signed off on the structural integrity; WWT is a yard inspection, not a certified grading
Container Grades at a Glance:
| Grade | What It Means |
|---|---|
| As-Is | No warranty, significant damage, possibly not watertight |
| WWT | Weatherproof, sealed, no CSC certification |
| CW | Marine surveyor certified, valid CSC plate, suitable for international transport |
| IICL | Premium used standard, set by the Institute of International Container Lessors |
| One-Trip (New) | Near-new condition, fresh CSC certification valid for five years |
WWT and CW cover the vast majority of used shipping containers for sale – knowing the difference between the two is genuinely the most useful thing you can walk away with.
Which One Do You Actually Need?
Go WWT if you need a container for storage — construction site, farm, commercial premises — and international shipping isn’t on the cards. It’s the most cost-effective and widely available option for storage needs, full stop. Smaller units like 10ft containers and 6ft shipping containers in WWT condition are particularly well-suited to domestic storage where space is tight and budget matters.
Go CW if you plan to transport cargo overseas, need CSC certification for port compliance, or simply want the flexibility to ship the container at some point in the future. It’s also the smarter long-term investment if you’re keeping the unit for years — the doors and floor tend to hold up better.
At Blue Fin International Shipping, we supply new and used shipping containers across Greater London and the UK. Not sure which grade suits your situation? We’ll help you figure it out without the guesswork.
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