Ladder

The Ladder is a basic building that provides vertical access while still allowing Duplicants to move horizontally across its top as if it were a tile. It is one of the most flexible early traversal structures in Oxygen Not Included because it does not block gas, liquid, light, or loose solid objects, making it useful for scaffolding, open shafts, and other layouts where airflow and permeability matter.

Duplicants can climb Ladders in either direction, and they can jump one-tile gaps to reach another Ladder or another valid walking surface. A Ladder also preserves walkable space on top of it, so it can serve as both a route and a platform. However, it does not count as solid ground, so buildings cannot be placed on it and ground-based critters such as Hatches will not walk on it. Ladders slightly reduce Decor, which makes heavy use of them less attractive in areas where Decor matters.

A few placement rules are important. Duplicants cannot climb onto a Ladder that sits directly under a ceiling; there must be one tile of clearance above it for passage. Meteors break Ladders, but broken Ladders still function, so damaged segments do not necessarily stop movement. Because Ladders do not block flow, they are often preferred in shafts that need to remain open rather than sealed.

For digging and early expansion, Ladders are especially efficient when placed in rows. From any given Ladder, Duplicants can dig two tiles to either side, four tiles above, and three tiles below. This makes it possible to excavate large areas efficiently by setting Ladders in staggered rows, skipping one tile between each Ladder and spacing the rows seven tiles apart. This pattern gives broad access while minimizing the amount of support structure needed.

Ladders are, however, slow to construct compared with Tile, so they are a poor choice for emergency access or quick containment. They are best used when you want mobility and permeability rather than immediate, solid flooring. In most colonies, they are most valuable in early mining, shaft access, and utility corridors where Duplicants need to move freely without sealing off the environment.

• Ladders can be built after a rocket launches, even though they cannot be built over rocket modules or engines.
• A line of Ladders placed one tile apart from the end of gantry platforms can give Duplicants full access to rocket modules.
• For rocket access, a heat-resistant material such as Igneous Rock is useful because it can withstand Hydrogen Rocket exhaust.
• Because Ladders do not block liquids or gases, they can be used in shafts where airflow must remain unobstructed.
• Because they do not count as solid ground, they are not a substitute for floors when placing buildings or supporting critters.