Container foundation, site preparation and unloading

Where a container rests: the four corners

ISO 1496-1, the standard for general cargo containers, requires a box to stand on its four bottom corner castings alone, the steel blocks at its lower corners; the underside of its base sits 12.5 mm above the bottom faces of those castings. It may also rest on its bottom cross members, the beams under the floor, but it is not built to bear on its bottom side rails, the long beams along each side. On soft or uneven ground a box settles into the soil and twists: the international code for packing containers warns that a grounded box deforms to the ground, its doors then bind, and it sinks. If the doors stand out of line, a shim, a thin steel plate slipped under one corner, usually straightens them.

Container foundation: piers, blocks, pads or slab

• For storage: four supports under the corners, level with each other, on firm and drained ground: concrete piers or pads, solid concrete blocks, or a plinth. The plan above shows where the corners fall. A pier of plain concrete 600 mm on each side takes 0.216 m³: about ₹1,700 of concrete at CPWD’s 2023 rate of ₹7,879 per m³, which includes GST and the contractor’s margin, so about ₹6,800 for four; digging and formwork are extra.
• For a long stay, an office or a home: a foundation designed by an engineer, with the box anchored to it; extra supports go under the cross members, not under the side rails, and since the underside of the base sits 12.5 mm above the corners, they stand that much higher than the corner supports, or are shimmed up. Twist locks and corner castings explains the anchoring, and the positions of the corners: 2,259 mm apart across the box, and 5,853 mm along a 20 ft one or 11,985 mm along a 40 ft one, centre to centre.
• A slab: suits a building made of several boxes; it needs drainage around it, so that rain does not stand under the floor.

The container house cost guide counts the piers, the crane and the haulage in its examples.

How high above the ground?

India’s Model Building Bye-Laws of 2016 ask for a building’s plinth to stand at least 450 mm above the surrounding ground, with drainage; each state adapts them, so ask your local body (permission to place a container). Raised on its supports, a box also keeps air under its floor, which slows rust.

Containers on stilts and in flood zones

Where water rises, the NDMA’s flood guidelines put the plinth of a building 0.6 m above the flood or submersion line, and allow homes on stilts in the zone of a 25-year flood, but not in that of a 10-year flood. The code for packing containers likewise advises setting a box on blocks where it could flood. Tall piers or columns under a container are a structure in their own right: ask an engineer, and anchor the box to them.

Termites

A container floor is made of timber boards. India’s standard for protecting buildings from subterranean termites, IS 6313 (Part 2), treats the soil under the building with chemicals; under a container, at least keep the floor clear of the soil and the space under it open to the air.

Access for the truck

• Height: under rule 93 of the Central Motor Vehicles Rules, a vehicle carrying an ISO container may stand 4.52 m tall overall. Look up for cables, branches, gate arches and balconies on the way in.
• Length: a tractor and semi-trailer may be 18.75 m long. A 40 ft trailer needs a wide, straight approach; a 20 ft one turns more easily. We found no Indian rule on the turning circle: walk the route with the transporter’s dimensions in hand.
• Ground: a loaded trailer, a side-lifter’s legs and a crane all press hard on the soil. After rain, a field can become impassable.

Four ways to unload a container

Can you lift a 20 ft container with a forklift? Fork pocket dimensions

Yes, if it has fork pockets, which ISO 1496-1 allows on 20 ft and 10 ft boxes only. The main pair, 2,050 mm centre to centre (give or take 50 mm), each at least 355 mm wide and 115 mm high, takes the box loaded or empty; an inner pair, 900 mm centre to centre, on some boxes, is for an empty box only. The forks must go in at least 1,825 mm. A 40 ft box has no fork pockets, and a box without them should never be lifted by forks. Ask the forklift’s owner whether it is rated for the box’s weight at that reach: about 2,230 kg for an empty 20 ft.

What is a side-lifter (side loader) trailer?

A trailer with cranes of its own that lifts the box off its deck and sets it down beside the road, or onto another truck. It saves the crane hire, but it needs the spot right next to where the truck stands, on firm ground with a slight slope at most: one maker advises no more than 2°. We found no side-lifter operator documented in India: ask the seller whether one works near you.

Container tilt trailer and tilt tray delivery

A tilt trailer, or tilt tray truck, tilts its deck so that the box slides off onto the ground behind it. We found no maker’s data and no Indian rate for it: if a seller offers one, ask what approach and what ground it needs, and whether the rear corners of the box will drag on your ground or on the supports.

Unloading with a crane: capacity and hire rates

Many Indian sites use pick-and-carry “Hydra” cranes, which move with their load. Their capacity falls fast with reach: one maker’s 12 tonne model lifts 12 tonnes at 1.7 m but only 2.3 tonnes at 8 m, while an empty 40 ft box weighs about 3,700 kg. Tell the crane company the tare of the box, 2,230 kg for a typical 20 ft and 3,700 kg for a 40 ft, and how far the crane will stand from the spot.

In what order?

1. Choose the spot and walk the route for height, width and ground.
2. Build the supports before the delivery, at the corner positions of your box, level with each other.
3. Tell the seller how the box will be unloaded, and ask for the trucking and the unloading as separate lines of the same quote: we found no public rate for a side-lifter or a tilt truck. The 20 ft and 40 ft container pages give the price of the box itself.
4. On the day, check that each corner lands on its support; shim a corner if the doors do not close square.

The container transport cost page gives what the trucking costs, and the delivered price estimate adds it to the box. Say which unloading you need when you ask for quotes.