Quick answer
In Ontario, a shipping container is considered level when the four corner castings sit within 1/2 inch of each other across the full footprint, measured corner to corner, side to side, and diagonally. Shims go under the corner castings only, never under the bottom rails or the floor cross members. Hardwood blocks work for short stacks under about 1 1/2 inches and indoor-protected sites. Galvanized steel plate shims are the right call for permanent installs, exposed sites, and any stack over that height. After the box is set, plan a re-check at 6 months and again at 12 months because Ontario frost cycles will move almost any pad a little in the first winter. If you are more than 2 inches out at any corner, stop and bring in a foundation contractor. Van Blanc has been delivering containers across Ontario since 1995, and the leveling rule has not changed in 30 years. Family-run Ontario shipping container supplier, 4.9 stars across 124+ Google reviews, 1-3 day delivery.
Why does leveling a shipping container actually matter?
Leveling a shipping container matters because the box carries its entire weight through four corner castings, not the ground beneath it. When one corner sits low, the steel frame twists. That twist binds the doors, ponds water on the roof, and flexes the floor. A box level within 1/2 inch operates cleanly for decades.
People hear “shipping container” and assume an 8,000 pound steel box does not care which way the ground tilts. It cares. A container is engineered to carry its load through four ISO 1161 corner castings, which are cast steel blocks welded into each corner. The bottom rails, cross members and floor are designed to span between those four points, not to bear against the ground. When a corner sags, the frame twists, and that twist shows up first at the doors.
“I tell every Ontario buyer the same thing on the phone before we set the wheels rolling,” says Christian LeBlanc, second-generation operator at Van Blanc. “A level box opens and closes for twenty years. A box set on dirt or on a single railway tie under the middle of the rail will fight you inside of one winter. The doors are the witness.”
Three things go wrong when a container is out of level beyond about 1/2 inch:
- Door binding. The cam locks on a 20 foot or 40 foot door are designed to clear by a few millimetres. A twisted frame either makes the doors swing on their own, or jams them closed.
- Water pooling on the roof. The roof is a thin corrugated sheet with a slight crown. A box tilted toward the back ponds water at the rear corner, which is exactly where corrosion starts.
- Frame stress and floor flex. Marine-grade plywood floors are bolted to steel cross members. When the box is twisted, the floor flexes every time you walk on it, the bolts loosen, and the plywood lifts at the seams.
How level does a shipping container need to be?
A shipping container needs to sit within 1/2 inch corner to corner across its full footprint. The industry rule of thumb, repeated in supplier guides from Conexwest to UK firms like Universal Containers, is that no corner should sit more than 1/2 inch above or below any other corner. For a 20 foot container, that is 1/2 inch across roughly 240 inches of length. For a 40 footer, that is 1/2 inch across 480 inches. It is a tighter tolerance than most foundations get poured to, which is why shimming is part of nearly every Ontario delivery.
Some suppliers tighten the rule further. The British outfit Quickfit recommends a 3/8 inch trigger for shimming on permanent installs, on the theory that pads settle and you want a buffer. At Van Blanc we use 1/2 inch as the must-fix line and 3/8 inch as the call-the-installer line for any box that will carry a roof load, a second-storey stack, or a sea-can-modified office.
The tolerance has to hold three ways at once:
- Corner to corner along each long side (front-left to rear-left, front-right to rear-right).
- Side to side at each end (front-left to front-right, rear-left to rear-right).
- Diagonal (front-left to rear-right, front-right to rear-left). Diagonal is the one most installers skip. A box can be level along both long sides and along both ends and still be twisted, which is the worst possible outcome for the doors.
What tools do you need to level a shipping container?
Leveling a shipping container takes a self-leveling laser, a hydraulic bottle jack, and shims sized for the gap. Here is the kit Christian’s crew carries on every Ontario delivery.
- Self-leveling rotary or cross-line laser. A spirit level on top of the rail tells you about that rail. A laser tells you about all four corner castings against one reference plane. For a 40 footer, this is non-negotiable. Set the laser on a tripod about 15 to 20 feet from one long side, level it, and read each corner casting against the beam.
- 20 ton hydraulic bottle jack with a steel pad. 12 ton works for a 20 foot empty box. For a 40 foot box, or any container with cargo or a build-out inside, step up to 20 ton. The jack goes under the corner casting only, never under the bottom rail and never under the floor.
- Hardwood shims. 6 inch by 6 inch oak or beech blocks, planed to consistent thicknesses (1/2, 1, 2 inches). Hardwood is acceptable for short stacks in protected locations.
- Galvanized steel plate shims. 6 inch by 6 inch minimum, 1/4 inch and 1/2 inch thicknesses. Hot-dipped galvanized resists Ontario salt and freeze-thaw. Use these for any permanent install, any stack over about 1 1/2 inches, or any exposed site.
- 4 foot spirit level as a sanity check on each rail after the laser pass.
- Tape measure for the diagonal check.
How do you check if a delivered container is level?
You check a delivered container by reading all four corner castings against one laser plane, then confirming the diagonals and operating the doors. The driver sets the box, drops the chassis, and pulls forward. You now have about ten minutes before the truck rolls. Use them. This is the same window we walk customers through during a typical Ontario delivery, right after the box settles onto the pad.
- Set the laser on its tripod, 15 to 20 feet away from one long side, perpendicular to the box. Level the unit and let it self-calibrate.
- At each corner casting, hold a tape measure vertically against the casting and read the height of the laser dot or line on the tape. Write all four numbers on a notebook or on the casting itself with a paint marker.
- Subtract the lowest reading from the highest. That is your corner-to-corner deviation. Under 1/2 inch and you are inside the tolerance. Over 1/2 inch and you have shimming to do.
- Check the diagonal. Run a string line, or use the laser at 90 degrees, between the front-left and rear-right castings. Repeat for front-right and rear-left. If the diagonals disagree by more than 1/2 inch, the box is twisted and needs a corner lifted.
- Walk to each door and operate it. The doors are the witness. If they swing on their own or bind in the cams, the numbers are lying to you somewhere.
Where do shims go under a shipping container?
Shims under a shipping container go beneath the four corner castings, never mid-span under the rails. This is the single most ignored rule in container installation, and it is the reason most “level” boxes still fail at the door inside two years.
Shims go under the corner castings. That is it. Not under the bottom rail at the middle. Not under the floor cross members. Not under a wooden block that is itself under the rail. The four corner castings are the only points on the box engineered to take concentrated load, and the bottom rails are designed to span between them with no support in between.
“We rolled out a thirty-year-old container last summer that had been sitting on three railway ties laid crosswise under the rails,” Christian recalls. “The middle tie had taken about an inch and a half of load over the years. The bottom rail had a permanent bow in it. The corner castings, which had carried almost nothing, were perfect. The frame had eaten the punishment that the castings should have taken. You cannot un-bend that rail.”
If your pad is not flat enough to clear the bottom rails, you have two options: raise the entire box on taller corner-casting shims so the rails have air under them, or go back and get the base right before the box lands. You do not bridge the middle.
Hardwood or galvanized steel shims: which should you use?
Choosing between hardwood and galvanized steel shims comes down to how long the box stays and how exposed the site is. Both materials are real options, and neither is wrong everywhere. Here is the call.
| Factor | Hardwood blocks | Galvanized steel plate |
|---|---|---|
| Best use | Short stacks under 1 1/2 inch, protected sites, temporary installs | Permanent installs, exposed sites, stacks over 1 1/2 inch, any second-storey stack |
| Compression | Compresses slightly under load, especially across grain | Effectively zero compression |
| Ontario weather | Absorbs moisture, freezes, can split or rot in 5 to 10 years | Hot-dipped galvanized, resists road salt and freeze-thaw indefinitely |
| Size | 6 inch by 6 inch minimum, planed | 6 inch by 6 inch minimum, 1/4 inch or 1/2 inch thick |
| Relative cost per corner | Lower upfront, but you replace split or rotted blocks every few years | Higher upfront, but you set it once and never touch it |
| Lifespan | 5 to 15 years in Ontario | 30+ years |
On a 30 year box that you actually plan to own for 30 years, the cost difference works out to pennies per year. Steel. That long ownership horizon is also why so many buyers who start with a freshly built one-trip unit spend the extra on steel plate from day one.
What is the lift, shim, and lower sequence?
The lift, shim, and lower sequence is the eight-step routine for raising each low corner casting, slipping a shim under it, and setting it back down without racking the frame. Once you know which corners are low and by how much, the actual shimming is a quiet, methodical job. Rushed shimming is what splits hardwood and dents castings.
- Identify the highest corner. That is your reference. You are not lowering it. You are bringing the other three up to meet it.
- Place the bottle jack under the lowest corner casting, with a steel pad spanning the jack head and the underside of the casting. The casting has a hole on the bottom face. The jack pad goes against the steel around the hole, not in it.
- Lift slowly until the casting clears the pad by about 1/8 inch more than the shim stack you intend to insert. A 20 ton bottle jack on a level pad will not flinch under a corner of an empty container, but lift smoothly anyway.
- Insert the shim stack directly under the corner casting. Centre it. The shim must be wider than the casting footprint so the load spreads onto the pad, not into the shim edge.
- Lower the jack slowly until the casting rests on the shim. Listen. A sharp crack means a hardwood block split, and that block is now garbage. Replace it before continuing.
- Repeat at each low corner. Work opposite corners in sequence so the box does not rack as you go. Front-left, then rear-right, then front-right, then rear-left, for example.
- Re-check the laser. Re-do the four-corner read. You are aiming for all four within 1/4 inch of each other, well inside the 1/2 inch tolerance.
- Operate every door. Doors are the final pass. If they swing freely from any position and the cams seat without forcing, the box is level enough.
Do you need to re-check level after the first winter?
Yes, you need to re-check a shipping container’s level after the first winter, at roughly 6 and 12 months. This is the step almost nobody does, and it is the difference between a 5 year install and a 25 year install. Ontario soil moves. Even compacted granular pads settle differentially. Even concrete piers heave a quarter inch on a bad winter. The box will move with the pad, which is why the choice between a deep pier and a gravel base changes how often you will be back out here with a jack.
Book two re-checks into your phone calendar the day the box lands:
- 6 month re-check. Late October or early November for a spring delivery. Run the laser pass again. Operate every door. If any corner is more than 1/2 inch out, shim it before freeze-up.
- 12 month re-check. One year after delivery. This catches the full freeze-thaw cycle. Most boxes that are going to settle have done their settling by month 12. If you pass this check, you are typically good for 3 to 5 years before the next look.
“The 12 month re-check is the one I beg every customer to do,” Christian says. “It takes 20 minutes. A 1/2 inch shim added in year one saves a door replacement in year seven.”
When should you stop and call a pro?
You should stop shimming and call a pro when a corner is more than 2 inches out, the box is visibly twisted, the doors will not seat, or anything is stacked on the roof. Shimming is owner-level work in most cases. There are four scenarios where it is not.
- More than 2 inches out at any corner. You are not dealing with a pad problem any more. You are dealing with a foundation problem. Get a foundation contractor or pier installer on site before you keep stacking shims.
- Box visibly twisted (diagonal more than 1 inch out). The frame may already be permanently deformed. You need a container repair professional, not more shims.
- Doors that will not seat even after re-leveling. The frame has racked. A welder needs to look at the corner posts.
- Second-storey stacks or roof-loaded containers. Anything carrying meaningful vertical load on top of the box should be set and inspected by a contractor with structural sign-off, not shimmed by the owner.
For routine 1/2 to 1 1/2 inch shimming on a single 20 or 40 foot box on a properly prepped Ontario pad, you can do it yourself with a laser, a jack, and steel plate. Anything beyond that, call us or call your contractor.
FAQ
How level does a shipping container need to be in Ontario?
Within 1/2 inch corner to corner across the full footprint, measured along each long side, each end, and both diagonals. Boxes set tighter than that, around 1/4 inch, will operate without door drift for many years. Boxes set looser than 1/2 inch typically show door binding within one or two seasons.
Where exactly do shims go under a shipping container?
Under the four corner castings only. Never under the bottom rails between the castings, never under the floor cross members, and never under a wooden block that is itself bridging the rail. The corner castings are the only points engineered to carry concentrated load.
Hardwood shims or galvanized steel shims for an Ontario install?
Hardwood is fine for short stacks under 1 1/2 inches on protected or temporary sites. Galvanized steel plate is the right choice for any permanent install, any exposed site, any stack over 1 1/2 inches, and any container you plan to own for more than about 10 years. Ontario freeze-thaw is hard on wood.
What size jack do I need to level a 40 foot shipping container?
A 20 ton hydraulic bottle jack with a steel pad against the corner casting. 12 ton is enough for an empty 20 foot box. Anything loaded, modified, or 40 foot long should get the 20 ton tool. Place the jack head on the casting steel around the bottom hole, never in the hole itself.
Can I level a shipping container with a spirit level alone?
For a 10 foot or 20 foot box on a small lot, yes, with care. For a 40 foot box, a spirit level is not long enough or accurate enough across that span. Rent or buy a self-leveling rotary laser. The diagonals especially are almost impossible to read with a spirit level alone.
How often do shipping containers settle in Ontario?
Most properly prepped pads settle slightly in the first year, primarily through one freeze-thaw cycle. After year one, settlement slows dramatically. Pads on undisturbed ground or on engineered piers may not move measurably for 5 to 10 years. Pads on disturbed fill or organic soil may keep moving indefinitely and may need a different foundation strategy.
Should I re-check level after the first Ontario winter?
Yes. Plan a 6 month re-check and a 12 month re-check after the box lands. Both should take 20 minutes with a laser. A 1/2 inch correction in year one prevents tens of thousands of small flex cycles on the doors and frame over the next decade.
Why are my container doors swinging on their own?
The box is out of level, and the door side is high. Gravity is pulling the doors toward the low corner. Re-level the box. If the doors still drift after the four corners are within 1/2 inch, the frame may be racked and you need to look at the corner posts and hinge welds, not the doors themselves.
Can I stack shims indefinitely or is there a height limit?
Practical limit for steel plate shims under a corner casting is around 4 inches. Beyond that, the load path is getting tall and narrow, and a side impact (a snowplow, a vehicle backing in) can tip the stack. Above 4 inches, switch to a concrete pier or a helical pier rather than more shims.
How much does it cost to level a shipping container in Ontario?
The cost depends on whether you do it yourself or hire it out. A DIY level is mostly the price of a laser rental plus your own steel shims for a one-time install, which is modest. Having it done alongside delivery in the Brantford and Hamilton region costs more because you are paying for the crew and the jack, but a routine 4-corner level on a freshly delivered box is still a small line item next to the container itself. The variables that move the number are how far out of level the box is, how many corners need shimming, and whether the pad needs correcting. Severely out-of-level boxes that need a foundation fix run higher and need a contractor, not a shim crew.
Talk to Christian about your delivery
Van Blanc has been delivering containers across Ontario since 1995, and we have 200+ units in stock across our 4 Brantford yards. Come walk the row, read the CSC plates, pick your box, and we will deliver inside 1 to 3 days. If you want the laser-and-shim treatment on day one rather than the “good enough, you’ll figure it out” treatment, that is a conversation worth having.
Sources
- Conexwest. How To Level Shipping Containers.
- Industrial Wheels. Corner Castings ISO 1161 for Shipping Containers.
- Quickfit Container Accessories. A Guide to Shipping Container Levelling.
- Universal Containers. How To Level A Shipping Container.
- Lotus Containers. Anatomy of a Shipping Container: Corner Castings and Twistlocks.
- Lease Lane Containers. Choosing the Right Base for a Shipping Container.
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