Lesson 3.2: Openings

Once you’ve planned your container project, one of the first physical steps is usually cutting in openings, whether that’s for a man door, sidewall window, vent, or even a full roll-up door. But unlike cutting into wood framing, a shipping container’s steel structure requires careful consideration to keep it strong, dry, and secure.

At Container Modification World, we provide pre-framed kits that make cutting into containers easy, but it’s still important to understand how and where to cut, what needs reinforcing, and how to protect the opening after the fact.

Let’s break it down.

What Counts as an Opening?

Any cut into the roof, sidewalls, end walls, or even the floor is considered an opening.

Know Before You Cut: Structural Considerations

Containers get their strength from the steel corrugation and corner framework. When you cut into a wall, roof, or floor, you remove part of that rigidity.

Key Risks:

Wall sagging or twisting
Roof oil-canning or buckling
Water ingress around unsealed openings
Reduced ability to stack or transport
Loss of insulation continuity

The solution? Reinforce every opening and only cut in areas that can be supported properly.

How to Properly Frame an Opening

Whether you're DIY-ing or working with a contractor, here’s the general rule:
Cut once. Frame immediately. Seal forever.

Step 1: Mark the Opening

Measure twice and use a level. Always account for the total kit size, including flange and trim overlap.

Step 2: Make the Cut

Use an angle grinder, plasma cutter, or recip saw with a metal blade. Protect yourself with PPE and watch for flying sparks.

Avoid over-cutting—especially on corners. Rounded corners are easier to reinforce and seal.

Step 3: Install a Framing Kit

Install a pre-framed man door, window, or vent kit from CMW. These are built with heavy-duty flanges and fasteners that tie back into the corrugation or steel studs.