Container Blocking, Bracing & Dunnage: A 2026 Guide

An ocean container is a harder environment than a truck

Freight that survives a thousand highway miles can still arrive from overseas as a pile of crushed cartons. The reason is that the two journeys stress cargo in completely different ways.

A truck mostly generates forward and lateral forces in bursts: braking, cornering, potholes. A container at sea is subjected to sustained, repetitive motion in several axes at once. The vessel rolls side to side, pitches bow to stern, heaves up and down, and racks the box itself as the hull flexes. Add the vibration from engines and the shocks from crane lifts, terminal handling and rail or chassis transfer at both ends, and cargo can be worked continuously for weeks rather than hours. Anything that can loosen will loosen.

Humidity compounds it. Containers pass through changing climates, and moisture that a truckload never encounters can soften cardboard, corrode metal and weaken the very packaging you were relying on for stability.

The practical implication: securement that is adequate for a domestic dry van is often not adequate for an export or import container. Plan for repeated low-level movement, not a single hard stop.

Plan the load before anything goes in the box

Most securement failures start as loading-plan failures. Decide the layout before the first pallet crosses the threshold.

Distribute weight front to back and side to side

Aim for weight spread as evenly as practical along the length of the container and balanced across the centerline. Heavy concentrations at one end or on one side create handling problems for the terminal and the trucker, and can put the loaded box outside legal axle limits once it is on a chassis, even when the total gross weight is fine. If you are near a weight limit, work out the distribution on paper first.

Avoid concentrated point loads on the floor

Container floors are designed to carry distributed loads, and heavy machinery on small feet or narrow skids can concentrate force in a way the floor was not intended to absorb. Spread the load using timber bearers, steel or timber spreader beams, or a purpose-built skid that increases the contact area. For anything heavy, unusually shaped or non-palletized, ask the container owner what the floor is rated for rather than assuming.

Keep the center of gravity low and centered

Heavy items go on the bottom and toward the middle. Light items go on top. A high or off-center center of gravity makes the container behave badly during lifts and increases the chance of shifting when the vessel rolls.

Fill the voids you create

Every gap you leave is room for cargo to build momentum. Plan the pallet pattern to minimize gaps in the first place, then fill what remains. If you are deciding between palletized and floor-loaded, our comparison of floor-loaded versus palletized containers and Miami devanning covers the securement and labor trade-offs on both sides.

The securement toolkit

• Dunnage bags (airbags): inflatable void fillers placed between cargo blocks or between cargo and the wall. Choose the bag size and ply rating for the gap and the load, and follow the manufacturer’s inflation guidance. They are for filling voids and restraining movement, not for compressing cargo into place.
• Lumber bracing and blocking: timber gates, uprights, cross-members and wedges nailed or bolted into a structure that physically stops movement. For international shipments the wood must comply with ISPM 15.
• Shoring bars and load bars: adjustable bars that span the width to hold a row in place or create a barrier at the door. Useful for light to moderate restraint and for keeping cargo off the doors.
• Strapping and lashing: polyester, composite or steel strapping and webbing lashings tensioned to lashing points. Match the strap type, tension and buckle to the load, and re-check tension after settling.
• Edge protectors and corner boards: put them under every strap that crosses a package edge. They spread the strap load and stop the strap from cutting into cartons, which is a common cause of strap loosening in transit.
• Void fill: honeycomb panels, inflatable pillows, foam and corrugated fillers for the small gaps airbags cannot handle.
• Friction mats: rubber or composite anti-slip mats under pallets or heavy items to raise the friction between load and floor, reducing sliding. They complement lashing rather than replacing it.
• Shrink and stretch wrap: effective for unitizing a pallet so it behaves as one block; not a substitute for blocking, bracing or lashing.

Palletizing quality drives everything downstream. If pallets arrive unstable, no amount of dunnage saves them; the same unitizing principles in our guide to palletizing freight to avoid damage claims apply inside a container.

Container-specific realities

Two assumptions cause a disproportionate share of damage.

Not every point is a lashing point. Containers have designated securing points, and their number, location and rated capacity vary by container type, age and owner. Do not lash to a random fitting, a door hinge or a corrugation because it looks strong. Verify which points are approved and what they are rated for with the container owner or leasing company, and confirm with your carrier before you plan a lashing scheme around them.

Container walls are generally not designed to be load-bearing. The corrugated sides resist cargo pressure to a limited degree, but they are not a bracing surface for heavy items to lean against. Build your restraint against the floor, the corner structures and approved securing points, and use void fill so cargo is supported without pushing hard on the walls. Where you do need to bear against a wall, spread the contact with timber or panels instead of concentrating it.

Also plan the door end deliberately. The last meter is where cargo tends to shift toward, and it is the first thing that meets an inspector or a devanning crew. A proper door-end gate or barrier keeps freight from falling out when the doors open, which is a genuine safety issue as well as a cargo issue.

Moisture control

“Container rain” happens when warm, moist air inside a container hits a cooler steel roof at night and condenses, then drips onto the cargo below. Over a multi-week voyage crossing climate zones, that cycle repeats. The results are stained and softened cartons, collapsed stacks, rust, mold and label failure.

Reduce the moisture you load in the first place. Wood, cardboard and some products carry water in with them, so use dry pallets and dry packaging, and avoid loading in rain when you can. Then manage what remains: container desiccants hung on the walls or placed between pallets absorb airborne moisture, and desiccant capacity should be matched to the voyage length and cargo, following the supplier’s guidance. Liners and covers can protect sensitive loads from drips. Check that any vents are clear and undamaged, and inspect the container interior for existing water stains, daylight through seams or a damp smell before loading — do a light check with the doors closed and reject a box that shows daylight at the seams.

ISPM 15 wood packaging for international moves

If your blocking, bracing, pallets or crates are made of solid wood and the shipment crosses an international border, the wood packaging material generally needs to be treated and marked in line with ISPM 15, the international standard for wood packaging. In practice that means heat-treated or otherwise approved material carrying the recognized stamp. Non-compliant wood is one of the more avoidable causes of a container being held, fumigated at your expense, or refused entry. Manufactured materials such as plywood and OSB are typically treated differently from solid wood, but requirements and enforcement vary by destination country, so confirm the current rules for your specific destination with your customs broker or the relevant national plant protection authority before you build. When crating is complex, professional packing and crating is usually cheaper than a rejected shipment.

Pre-departure inspection and photo documentation

Photographs taken during loading are the single most useful thing you can have when a claim is filed. Once the doors close, nobody can prove how the load looked.

• Photograph the empty container interior, including the floor, walls, roof and door seals, with the container number visible.
• Photograph the load in stages: the first tier, the mid-point, and the finished load at the door.
• Capture close-ups of each securement element — lashings, strap tension, airbag placement, bracing structure, friction mats.
• Photograph the ISPM 15 stamps on the wood you used.
• Photograph the closed doors with the seal number legible.
• Confirm placards, labels and documentation for hazardous or regulated cargo.
• Verify the weight declaration against your load plan.
• Note who loaded, when, and under what conditions.

Because standards for securement in intermodal transport are set out in guidance such as the CTU Code and in carrier-specific requirements, and those change over time, treat the above as a planning framework and verify the specific ratings, methods and documentation with the container owner, your carrier and your insurer.

The South Florida angle

For importers moving boxes through PortMiami and Port Everglades, the real test of the load plan comes at devanning. A container braced properly unloads quickly and cleanly; a shifted or poorly braced load turns into hours of labor, damaged product and a claim. Go Freight handles container drayage for PortMiami and Port Everglades and devans into our 100,000 square foot Miami/Medley warehouse, so any securement or moisture problem is documented with photos at the moment the doors open rather than discovered later. South Florida’s heat and humidity also make desiccant planning worth taking seriously on inbound freight, not just outbound.

Frequently asked questions

Can I lash cargo to any point inside a container?

No. Only designated securing points should be used, and their number, location and rated strength vary by container type, age and owner. Never assume a fitting is rated simply because it looks strong, and never lash to door hardware or corrugations. Confirm which points are approved and what they can take with the container owner or leasing company and your carrier before you plan the lashing scheme.

Do dunnage bags replace blocking and bracing?

No. Dunnage bags are void fillers that stop cargo from building momentum in gaps. They work best alongside blocking, bracing, lashing and friction mats rather than instead of them. Heavy or high-value loads generally need a physical structure that stops movement, with airbags filling what remains.

Does all wood in my container need ISPM 15 treatment?

Solid wood packaging material, including pallets, crates and the lumber used for blocking and bracing, generally needs to be treated and marked under ISPM 15 for international shipments. Manufactured materials such as plywood are typically handled differently. Requirements and enforcement vary by destination, so confirm the current rules for your specific country with your customs broker.

Shipping containers in or out of South Florida? Call (786) 449-4020 or email rates@gofreighthub.io and we will help you plan the load, the drayage and the devanning together.