How do you expand your ship in Ostranauts?

Build hull — walls and floors — outward from your existing structure, then seal and pressurize the new space. All hull pieces connect to each other regardless of brand, so you can extend with whatever you salvaged.

Does my ship have to be airtight?

No. Ships don't have to be airtight, but you want at least one properly pressurized space for safety. Plenty of players run a sealed core with unpressurized storage bolted around it.

Why won't this object fit where I want it?

Because tiles have layers. Equipment and storage racks occupy the lower space, while lights, vents and overhead bins use the upper space — and some items quietly need subfloor room, like subfloor bins needing space to open and fusion tanks needing space for piping.

Ostranauts Ship Building — How to Expand Your Ship

Expanding your ship means building hull outward and then making the new space livable — and the thing that trips everyone up isn’t the building, it’s the layer system. Learn the layers first and most “why can’t I place this” problems disappear.

The layer system (read this before you build anything)

Every tile on the grid is not one space — it’s a stack:

Layer	What lives there	Gotcha
Subfloor	You never build here directly, but things reach into it	Subfloor bins need the room to open; fusion fuel tanks need it for piping. A tile can look empty and still be spoken for
Floor	Airtight flooring, plus subfloor bins and cargo web	Floor tiles can go under walls but aren’t required to
Lower space	Equipment, loose objects, storage racking — and you	This is the layer that fills up fastest
Upper space	Lights, vents, overhead bins, air pumps	Free real estate people forget about. Move your lighting and vents up here and the floor breathes
Ceiling	Power conduits only	Doesn’t need to be sealed by hull pieces

Most objects take up only one of upper/lower — which means a corridor that feels full at eye level usually has an entire unused layer above it.

Hull: mix and match freely

Ship hulls are just walls and floors. Different brands have different stats, but all hull pieces connect to each other — so the mismatched plating you pulled off three different derelicts will bolt together fine. Ugly, functional, very Ostranauts.

A sane expansion order

Plan the airlock first. Where people and cargo enter decides the whole layout. Retrofitting an airlock is miserable.
Build the shell, then seal. Walls and floor, then check for leaks before you furnish anything.
Pressurize and check life support before moving equipment in — new volume means new air to manage (life support).
Assign the room type. An enclosed space isn’t a functional room until it meets that room’s requirements — see rooms for the needs/forbids table.
Furnish by layer. Lights and vents up, equipment down, storage wherever it actually fits.

Where the parts come from

You don’t buy most of this — you cut it off dead ships. Salvage is the supply chain for hull, and it’s also where the cheap version of every component comes from. If you’re adding a fusion setup while you’re at it, read reactor before you commit floor space, because it wants subfloor room for piping.

When to stop expanding

More volume means more air to heat, more mass to move and more hull to keep sealed. A tight, sealed, well-lit ship beats a cavernous half-pressurized one every time — especially before you have crew to help maintain it.

Layer and hull mechanics above come from the official wiki’s Ship Building page. If 1.0 changed specific placement rules, this page gets updated — the layer model itself is the stable part.