Hearts of Iron 4 (HOI4) – How to Unlock More Building Slots

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In Hearts of Iron 4, players will need to build a lot of factories, dockyards, and synthetic refineries to get all the resources they need to win World War 2.

However, they can’t really get what they want if there is a hard Building Slot limit of 2 in most of their states. Countries like Brazil and Canada suffer from huge territories with a really low Building Slot limit.

Recommended Read: How to Get Air Superiority in Hearts of Iron 4

This will probably make you wonder how to unlock more Building Slots in HOI4 to get more industry and overpower your peers.

Well, the most common way to unlock more Building Slots in Hearts of Iron 4 is to research Industry (Concentrated or Dispersed) to get double the Building Slot limit by 1943.

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How to Unlock More Building Slots in HOI4

There are three ways to unlock more Building Slots in HOI4:

  • Industry Technology
  • Region-wide Industrial Integration Decision
  • Industrial Land Appropriation Decision

There are also some countries that get Building Slots from their focus trees, but that is different for every country.

Most of them just receive free factories from the focus tree that come with a Building Slot to allow you to build as if nothing changed.


In the Industry side of the Research menu, you will find two lines of technology under Production which are called Concentrated Industry and Dispersed Industry.

You can only choose one of them, and they will either offer a lot better Production Output or defense from bombings and better retention.

Either way, both Concentrated and Dispersed Industry research technologies in HOI4 will increase your Building Slots. Each level of research in these techs will increase your Building Slot limit by 20%.

At the last level of each research line, you will get in total 100% more Building Slots. Depending on the states, this can either make a huge difference or almost no difference at all.

Still, at least you know that you should advance the Industry research as far as possible to unlock more Building Slots in HOI4 and get the most out of each state.

Region-wide Industrial Integration Decision

The second way to unlock more Building Slots in HOI4 is to get maximum Infrastructure in a state (level 5) and complete the Region-wide Industrial Integration decision for 100 Political Power.

If you get level 5 Infrastructure in a state, you will find a new decision in the Decisions menu called “Region-wide Industrial Integration.” This decision will cost 100 PP, and it will give you one extra Building Slot in that state.

Though this is not necessarily incredible, it is the only universal way to consistently increase the base amount of Building Slots in a state.

This can make a huge difference since, in states that only have 1 or 2 Building Slots, the bonus from technology also increases due to this base flat increase.

So, a state that had 1 Building Slot at the start of the game would normally get 2 from tech in 1943. However, if you use this decision, it will increase to 4 slots.

The only problem is that Infrastructure 5 isn’t really worth the Civilian Factories most of the time.

Infrastructure should only be built in states with really good resources, and those usually have a decent amount of Building Slots.

You also have to give 100 PP, which is a lot in the earlier parts of the game.

This can be useful later in a playthrough when PP doesn’t matter as much, but by that point, you should have conquered new land to build your factories.

Players can only use this decision for a specific state once, which means you can’t continuously increase the Building Slots in a state using this method.

Industrial Land Appropriation Decision

The third way to unlock more Building Slots in HOI4 is to go to war and complete the Industrial Land Appropriation decision for 50 Political Power.

When you go to war against any country in the game (even civil wars count), you get a new decision in the Decision menu called “Industrial Land Appropriation.”

For 50 PP, you can increase the Building Slot by 1 in a random state, but you will also lose 2.5% Base War Support and Stability.

There’s no time or cooldown on this decision besides the fact that you have to wait for the day to end.

You can use this decision endlessly to unlock a new Building Slot in all of your states. However, this could ruin your country if you don’t keep an eye out on Stability and War Support.

Though Stability can often be raised with decisions, War Support is a hard stat to increase.

Luckily, high World Tension will boost War Support for most countries to 100%, so you can generally start messing with this decision once WW2 starts.

In general, you shouldn’t really use this decision since both Stability and War Support are very important.

If one of them gets below 50%, you risk getting horrible events that will ruin your economy and make you waste a lot of PP.

If you really want to use this decision, try to time using it only if you know there won’t be huge changes to your main country stats.

Maximum Number of Building Slots You Can Unlock

Considering the three methods we have listed above, you can get a base 4 Building Slot increase in HOI4 by using them all.

If you were to take a state with 0 Building Slots, you can bump that up to 4 using decisions and technology.

However, for big states (population-wise), the only method that really helps is research. A state such as Moscow won’t really need 2 extra Building Slots.

However, technology can increase Building Slots up to 25, the maximum amount you can get in the game.

The biggest states in HOI4, such as the Greater London Area, start with 12 unlocked Building Slots.

Research can get that up to 24, and you would need one of the decisions to get the final slot.

However, there will usually be a national focus that will build a factory there and add an extra slot, so you won’t really need the decisions.

Can You Unlock More Building Slots Using Cheats/Commands?

Though there is no cheat to unlock more Building Slots in HOI4, you can use a combination of cheats to get what you want.

For example, you can use the “research_on_icon_click” or “researchall” cheats to get all the Industry research done and get the 100% bonus on Building Slots in states.

You can also use the Industrial Land Appropriation decision once at war as much as you want since you can just boost War Support and Stability back using cheats.

You can also get Infrastructure level 5 in all states using the “instantconstruction” cheat and use the Region-wide Industrial Integration decision.

That’s everything you need to know about how to unlock more Building Slots in Hearts of Iron 4!

Have any input or suggestions for this guide? Let us know in the comment section below.

Adrian Oprea

Based in London, United Kingdom, Adrian Oprea is a Guides Writer. As a professional single-player RPG player, Adrian has often been stigmatized. He has decided to pour his frustration into writing guides!

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