Building a functional and safe underwater base is one of the most rewarding aspects of Subnautica 2, but it comes with a critical mechanic that can end your run in seconds: hull integrity. Every compartment you add, every window you install, and every meter of depth you descend reduces your base's structural strength. When hull integrity drops below zero, your base floods — and flooding spreads fast. This guide explains the complete hull integrity system, the depth-pressure relationship, how to prioritize reinforcement modules, and the safe depth thresholds you need to know before placing a single foundation block.
How Hull Integrity Works
Hull integrity represents the structural strength of your base relative to the water pressure at its current depth. Every base starts with a base integrity value that depends on the foundation piece. From there, each additional module either adds to or subtracts from your total integrity score. The goal is simple: keep your total integrity above the pressure penalty at your current depth.
Pressure penalties scale exponentially with depth. At 100 meters, the penalty is negligible. At 300 meters, it becomes significant. Below 500 meters, even a single miscalculated module can push you into negative territory. The game does not warn you with a clear alarm until you are already at risk — by then, it may be too late to fix without emergency patching.
Base Integrity Formula
The core formula that governs your base is straightforward but unforgiving:
- Base Integrity = Foundation value + Sum of all module values + Reinforcement bonuses
- Pressure Penalty = Depth in meters × Pressure coefficient (0.5 per meter above 100m)
- Net Integrity = Base Integrity − Pressure Penalty
When Net Integrity drops to zero or below, the base enters a flooding state. Flooding begins in the weakest compartment (usually the one with the most windows or the highest local pressure differential) and spreads to adjacent rooms within 30 seconds. Once a room floods, all equipment inside is destroyed, and you lose oxygen access in that section.
Always build your base planner tool before placing any modules. The planner shows a real-time integrity preview, including depth penalties, so you can test different layouts without committing resources. A five-minute planning session can save you hours of rebuilding after a collapse.
Depth vs Pressure Relationship
Water pressure is the invisible enemy of every base builder. The deeper you go, the more crushing force your base must withstand. Understanding the exact thresholds at which pressure becomes dangerous is essential for choosing where to build and how to reinforce.
| Depth Range | Pressure Penalty | Build Risk | Recommended Action |
|---|---|---|---|
| 0–100m | 0 | None | Safe for any standard layout without reinforcement |
| 101–200m | 50–100 | Low | Avoid excessive windows; standard rooms are fine |
| 201–300m | 100–200 | Moderate | Use 1–2 reinforcement modules per 4 rooms |
| 301–400m | 200–350 | High | Reinforce every room; avoid windows entirely |
| 401–500m | 350–550 | Severe | Full reinforcement mandatory; use bulkheads |
| 500m+ | 550+ | Extreme | Specialized deep modules only; zero windows |
The 300-Meter Threshold
The 300-meter mark is the most important breakpoint for base builders. Above 300 meters, standard I-compartments and multi-purpose rooms can generally maintain positive integrity with minimal reinforcement. Below 300 meters, pressure penalties accelerate dramatically, and the cost of each additional room increases exponentially.
If you are planning a deep outpost for mining Kyanite or accessing Lost River resources, expect to dedicate a significant portion of your build to reinforcement. A deep base at 450 meters requires roughly three times the titanium investment of a shallow base at 200 meters for the same functional footprint.
Never build below 400 meters without at least two bulkhead doors. Bulkheads compartmentalize flooding, preventing a breach in one room from flooding your entire base. Without them, a single integrity failure at depth can destroy hours of progress in under a minute.
Module Integrity Values
Every base module affects hull integrity differently. Some add strength, while others subtract it. Knowing the exact value of each module allows you to optimize your layout for maximum functionality per integrity point.
| Module | Integrity Value | Notes |
|---|---|---|
| I-Compartment | +10 | Basic room; most efficient integrity per space |
| L-Compartment | +8 | Corner piece; slightly lower integrity |
| T-Compartment | +8 | Junction piece; useful for branching layouts |
| X-Compartment | +6 | Cross junction; lowest integrity, use sparingly |
| Multi-Purpose Room | +12 | Best integrity for large rooms |
| Observatory | +5 | Glass dome; very weak structurally |
| Window | −4 | Each window reduces integrity |
| Reinforcement | +7 | Best integrity-to-cost ratio |
| Bulkhead | +3 | Low integrity but critical for flood containment |
| Foundation | +15 | Required for all base starts |
Window Penalties Add Up Fast
Windows are the silent killer of deep bases. Each window subtracts 4 integrity points — which does not sound like much until you install four of them in a multi-purpose room at 350 meters. A room that should have +12 integrity becomes −4 after windows, requiring two reinforcement modules just to break even.
For bases below 250 meters, the rule is simple: no windows. The view is not worth the structural cost. If you absolutely need visibility, use the observatory module instead — it has a built-in reinforcement frame that partially offsets its low integrity score, and its panoramic view is superior to standard windows anyway.
Reinforcement Module Priorities
Reinforcement modules are your primary defense against pressure. They cost 2 Titanium and 1 Lithium each, making them relatively affordable, but placement priority matters. Reinforcing the wrong room first is a common mistake that leads to preventable collapses.
Priority 1: Rooms at Maximum Local Depth
If your base is built on a slope or overhang, some rooms will be deeper than others. The pressure penalty is calculated per-room based on its specific depth, not the base's average depth. Always reinforce the deepest rooms first, even if they are smaller or less important functionally. A flooded deep room will spread to shallow rooms faster than the reverse.
Priority 2: Rooms with High Window Count
Any room with two or more windows should be reinforced immediately upon installation. The cumulative penalty from windows creates a weak point that the flooding algorithm targets first. One reinforcement module per window is a good rule of thumb.
Priority 3: Central Junction Rooms
The room that connects the most other rooms — typically your main corridor or T-junction — should be heavily reinforced. If this room floods, it cuts off access to entire wings of your base. A reinforced central hub with bulkheads on each branch is the gold standard for resilient base design.
| Priority | Target Room | Reinforcements Needed | Rationale |
|---|---|---|---|
| 1 | Deepest room(s) | 2–3 per room | Highest pressure penalty; flood spreads upward |
| 2 | High-window rooms | 1 per window | Negative integrity attracts flooding algorithm |
| 3 | Central junctions | 2–3 per hub | Structural backbone; failure isolates wings |
| 4 | Power/generation rooms | 1–2 per room | Equipment loss cripples base functionality |
| 5 | Storage and living quarters | 1 per room | Lowest priority but still worth reinforcing |
Place reinforcement modules on exterior walls rather than interior walls. Exterior reinforcements receive a hidden +1 integrity bonus from direct contact with the seabed pressure distribution. This bonus is small but adds up across multiple modules, and it costs nothing extra.
Safe Depth Thresholds for Construction
Not all base purposes require the same depth. Building deeper than necessary wastes resources and increases risk. Here are the recommended maximum depths for common base types:
- Starter Base / Surface Outpost: 0–150 meters. No reinforcement needed for basic layouts.
- Mid-Game Resource Hub: 150–300 meters. Light reinforcement (1 module per 3 rooms) sufficient.
- Deep Mining Outpost: 300–450 meters. Heavy reinforcement mandatory; bulkheads required.
- Extreme Depth Research Station: 450–600 meters. Specialized deep modules only; zero decorative elements.
- Maximum Depth Emergency Shelter: 600+ meters. Not recommended for permanent bases; use mobile vehicles instead.
The Observatory Exception
The observatory module has unique properties that make it viable at depths where normal windows would be suicidal. Its hemispherical shape distributes pressure more evenly than flat glass panes, and its built-in frame provides a small integrity bonus. An observatory can safely operate at up to 400 meters with a single reinforcement module, making it the only acceptable glass structure for deep bases.
Collapse Prevention and Emergency Response
Even with perfect planning, accidents happen. A sudden depth increase from terraforming, a miscalculated module addition, or a glitch in the pressure calculation can push your base into negative integrity. Knowing how to respond in the critical first 60 seconds is the difference between a minor repair and a total loss.
Early Warning Signs
The game provides three warning signs before a full collapse:
- Audible creaking: A low metallic groan indicates integrity is within 10% of the pressure penalty. This is your first warning.
- Visual cracks: Small fracture lines appear on walls and ceilings when integrity drops below the pressure threshold. At this stage, flooding has not started yet.
- Water seepage: Droplets form at joints and seams. You have approximately 15 seconds before full breach.
Emergency Protocol
If you observe any of these signs, execute the following protocol immediately:
- Stop all construction. Do not add any more modules — they will only accelerate collapse.
- Seal bulkhead doors. Isolate the affected room to prevent flood spread.
- Equip repair tool. Stand by to patch breaches as they form.
- Add emergency reinforcement. If you have titanium and lithium in storage, craft and place reinforcement modules on the affected room's walls.
- Evacuate non-essential items. Move stored resources to unaffected rooms or vehicles.
Do not attempt to deconstruct modules to restore integrity during an active breach. Deconstruction takes 10 seconds per module, and the flooding algorithm accelerates when it detects structural changes. You will lose both the module and the base. Always reinforce, never deconstruct, during emergencies.
Summary: Build Smart, Build Deep
Hull integrity is not a mechanic designed to punish players — it is a system that rewards careful planning and thoughtful engineering. By understanding the depth-pressure curve, respecting module integrity values, prioritizing reinforcement placement, and knowing your emergency protocols, you can build safe, functional bases at any depth the game allows.
Remember the cardinal rules: plan before you build, reinforce your deepest rooms first, avoid windows below 250 meters, and always install bulkheads on multi-room bases. Follow these principles, and your underwater home will stand strong no matter how deep you dive.