Sol One Pressurized Base Guide: Airlocks, Seals and Oxygen Flow

The first time you take your helmet off in Sol One should be a deliberate act. Not because the game punishes curiosity, but because "inside" is a geometric state and "pressurized" is a physical one, and the game tracks them separately. A room can be fully enclosed, well lit, furnished and still be at Mars ambient pressure. Learning to tell the difference is the single most useful skill in the first ten hours.

This page is the deep dive on that difference: what makes a volume seal, how an airlock is supposed to work, how oxygen reaches the rooms you use, and how to test a habitat without gambling your run on it.

Sealed is a topology problem

A pressurized volume needs three things and only three things:

1. A closed boundary. Floor, walls and ceiling with no gaps. Doorways count as gaps unless a door is installed and closed.
2. A pressure-tight door. An open doorway, a window frame without glass, or a wall section that was placed but not finished all break the boundary.
3. A gas source. A sealed room with no oxygen supply is a vacuum with nice furniture.

The failure mode is almost never the wall itself. It is a joint: a wall placed against a foundation that has a one-tile gap, a ceiling that does not quite meet a wall run, a second door added for convenience and left open. In a grid-based builder, "looks closed" and "is closed" diverge at corners.

The three-state test

Before you trust a room, run this sequence:

• Open state: stand outside, look through the doorway. You should see the interior. Nothing is sealed yet.
• Closed state: close every door and check the interior atmosphere readout. If it is still tracking the outside, the boundary is broken.
• Pressurized state: with the oxygen source running, the interior should climb away from ambient and hold. If it climbs and then falls, you have a leak that the producer is outrunning.

A room that passes the third test is a habitat. A room that passes only the second is a shelter. Both are useful; only one lets you remove the suit.

How an airlock is supposed to work

An airlock is a small sealed chamber with two doors in series. The sequence is:

1. Outer door opens, you enter, outer door closes.
2. The chamber equalizes to habitat pressure — or you wait for it, depending on how the build handles cycling.
3. Inner door opens, you enter the habitat.

The purpose is not to keep air in. It is to avoid dumping the habitat's atmosphere onto the surface every time you walk in. A single door does exactly that: each entry is a small, repeated loss, and over a session it becomes a large one.

Practical airlock rules:

• Two doors, never one. If the module has a single opening, it is a vestibule, not an airlock.
• Keep it empty. Storage crates in the airlock eat the floor space you need to stand in a suit.
• Put it on the working side. The side facing your furnace, rover bay or resource pile. You will use it constantly.
• Light it. A dark airlock is where you fumble the door and vent the base.

The suit room is part of the airlock system

The Early Access build introduced suit, helmet and oxygen tank handling, which makes a dedicated transition room worth the space. The flow becomes: surface → airlock → suit room → habitat. You drop the pack, refill the tank, and keep dust out of the living volume.

This is also your emergency buffer. If the habitat loses pressure, the suit room is a smaller volume to keep breathable while you find the leak.

Room volume is a cost, not a feature

Every cubic metre of pressurized habitat is air you have to produce and heat you have to supply. A cathedral ceiling is a beautiful way to triple your oxygen bill. This is why the starter base should be small and why corridors should be short.

A useful mental model: oxygen consumption scales with pressurized volume, not with how many rooms you have. Two small rooms cost less than one large hall. If you want a big room, build it as an unpressurized workshop or a later greenhouse, and keep the living space compact.

Getting oxygen to every room

There are two ways a base fails at distribution even when production is fine:

• Dead rooms. A sealed room with no vent, duct or connected atmosphere never receives the oxygen the producer makes elsewhere.
• Pressure holes. An interior door left open between a pressurized room and an unpressurized annex drains the good room into the bad one.

The fix is a simple rule: every pressurized room must be connected to the oxygen source by a path that is itself sealed. If the path passes through an unpressurized space, the room is not on the loop. The oxygen guide→ covers producers and storage; the life-support loop→ covers how oxygen, water and power depend on each other.

Leak hunting

When the interior climbs but does not hold, you have a leak the producer is masking. Find it before you expand, because a marginal seal becomes a catastrophic one when you add volume.

A method that works:

1. Shut off the producer and watch the decay rate. Fast decay means a large opening; slow decay means a joint or a door seal.
2. Walk the boundary from outside. Look for a wall segment that does not meet its neighbour, a ceiling tile that is one grid short, or a foundation edge with a gap.
3. Check every door. Including interior doors you installed for convenience. A door that does not close flush is a leak.
4. Check the roof last but check it properly. Roof gaps are invisible from inside and obvious from a distance.

Do not tear the room down on the first failure. Most leaks are one piece.

Pressure and the rest of the base

A pressurized habitat changes how you use the rest of the base:

• Workshops stay unpressurized or separately sealed. Furnaces, cutting and fabrication produce heat and dust. Keeping them outside the living volume means you can work without spending air.
• Greenhouses are sealed, but they are their own atmosphere problem. Crops need light, water and carbon dioxide; a greenhouse that shares the habitat's air is a humidity and heat load on the life-support system.
• Rover bays are not habitats. Park the Crawler, close the bay, but do not expect to take your helmet off there unless you built it as a sealed volume with its own airlock.

What to build first, in order

1. One small sealed module, one airlock, one oxygen source.
2. Test the seal with the producer off.
3. Pressurize the module and confirm it holds overnight.
4. Add the suit room.
5. Add the workshop as a separate, unpressurized annex.
6. Only then add a second pressurized room.

This order protects you from the most expensive mistake in the game: building a beautiful multi-room habitat on top of a seal that was never tested.

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FAQ

Why does my habitat lose pressure at night? Cold and power loss are the usual causes. If heating or the oxygen producer shuts down when the battery drains, the room stops holding its state. Fix the power budget before you enlarge the room.

Can I pressurize a room with a window? Yes, if the window is a proper sealed piece. A frame without glass is a hole. Check that the window counts as part of the boundary in the build system.

Do interior doors need to be closed? Only the ones between pressurized and unpressurized volumes. Interior doors between two pressurized rooms can stay open, and usually should, because that lets air circulate.

How many airlocks does a base need? One per exterior entrance. A second airlock on the opposite side is a convenience later, not a requirement early.

Can I repressurize a room after a breach? Yes. Seal the breach, restart the oxygen source, and wait for the volume to recover. The cost is the gas you lost, which is why leak testing early is cheaper than repairing late.