Short answer: 5°C and below.

From what my experiment with Stew Piles that I place them in the stockpile zone around the town.
Here is the result:

1. In the field outside, 23.9°C, take 2 days to rot.
2. In the field outside (raining), 11.5°C, take 4 days to rot.
3. In the wooden house, 19.4°C, take 5 days to rot.
4. Underground, 7.2°C, take 20 days to rot.
5. Underground (deeper), 4.4°C, never rot.
6. Underground (deepest), -1.8°C, never rot.

Since the stair doesn't separate rooms from each other, which mean if you dig the ground as I do in the screenshot below, it will count as one room, so this mean the lower floor will have the same temperature as the top floor.


If you make a stair like this, it will be a little more difficult for the temperature to go down when you dig down, because it will average the temperature from every floor. The simple solution is to create a new room at the lower floor and separate it from the main stair with a door.

You may think that the temperature is lower because you are at the lower floor. But the truth is, what make your room temperature drop is what it is that stay above your room.

Let's see more example of what I did before I explain furthermore.


As you can see that room A, B, and C, are directly above from each other and separate by a simple wooden floor. While room D is in the same floor as room A, and room E is in the same floor as B.

You may noticed that room D and E have lower temperature than room C even it is on the upper floor. Why? Because there is a chunk of dirt above it to protect the heat rather than three slim floors of wood, which is very logical. This can be explain more in my drawing below.

I was surprise to find out about this at first, when you build the wooden floors in the room underground, it will generate some heat which you need to be considering when building cold room underground. Let's see the example:


This is the same 3x3 room which is located two floor below ground. The one on the left have nothing on the floor and the temperature is -2.2°C. Then, I built 3x3 wooden floors in that room as you can see in the right of the picture. The temperature suddenly increase to 1.1°C, this can be conclude that the floor did generate some heat underground.


However, this rule doesn't seem to be apply with the room above ground. As you can see in the above screenshot is that the room without floor in the left has 12.2°C, while the room with wooden floor in the right has only 12.7°C which is not change very much (it's increase a little bit, because the outside temperature increase).

This is another surprise thing that I found out, every room have floor radius two more block away from the floor inside the wall. This may sound confusing, so let's me show you another example photo.


From this photo, I build a room of 3x3 underground in the yellow line with wooden floor, and the blue line is the room radius. As you can see from the info box, they count every thing in room radius, so there are 10 wooden floors as in orange line, and 1 wooden door in the cross orange line with the room temperature of 1.1°C.


Another example, it is a 3x3 underground room in yellow line with wooden floor, and the blue line is the room radius. This time, the info box say there are 29 wooden floors because it's count every floor in radius even it is outside the room. In the previous rule, we knew that the underground wooden floor generate heat, and with these 29 wooden floors, the room temperature suddenly jump to 7.4°C, so better watch out.

Since, the floor doesn't generate heat above ground. So, you don't need to worry about this rule above ground. I still don't know why this rule exist, it look like the radius only count wall and floor as part of the room, but not the furniture. So, you can't create a Library with book shelf on the outside of the room.

While I experiment thing underground, I noticed something from the stair rule about expanding your room vertical and then the room temperature will be averaged from each floor.


Then, I wonder what the temperature will be if I expand horizontal. So, I create two building with the same material, same wooden floor, wall, door, and thatched roof. The only different is it size. Turn out the big one has lower room temperature at 19.5°C, while the smaller one has 21.9°C. Therefore, room size is matter somehow.


This is also true, with the underground room. As you can see, room A which has a bigger room size also colder than room B.

Short Answer: Yes, but maybe not worth it.

So, from what we learn so far, we need a chunk of dirt above room because it is better than roof and floor in order to protect room from heat, and we need a very large wall to make our storage room deeper from the sun. And this is what I come up so far...


Yep. It is pyramid of dirt which allow you to store a 3x3 square in the center. I manage to reduce the temperature from 22.6°C to 14.3°C with this method. If I keep adding wall and roof, the temperature will slowly drop later.

But as you can imagine how much time and resource you need to complete it, which I think it isn't worth the time and resource to do. Also, you can make a room bigger to reduce more heat, but you will need more material to make wall and roof also.

So, in this last section, I will show you my best method to create the cold storage room. What I consider most is that these methods can be done in 1-2 day early game, with minimum resource needed, and can be done with any villagers you got.


If you start your game in a mountain map, then considering put your food storage room in the nearest mountain step by digging a tunnel. The longer tunnel you dig, the more lower temperature you get. As you can see in my screenshot, I got -1.8°C room temperature from 15.5°C outside. But this method has one downside is that if you hit a metal vein while digging, it will take a much longer time, and since it's a one block tunnel, so only one of your villager can dig at a time.


For any other scenario, just dig two floor down the ground as in the screenshot and create a room at the end of the stair, I can get 4°C from 22.5°C sunny day.


If you somehow still want to get lower temperature, you can create bigger room and remove floor around the room as in the screenshot above. Since those wooden floor did generate a heat somehow, removing them will cause the room to be cooler, but don't forget that your food need to be on the wooden floor, so don't zone your food storage on dirt. With this method, I did lower my temperature to 3°C.


As you can see, by removing another outer layer of wooden floor, I manage to lower my temperature again to 0.6°C. So, basically just keep expand the room without building the floor, the temperature will keep getting lower.


This is my current design for cold storage, which I decide to separate room into many parts as a cooling unit and storage unit. But if you start to understand a concept of temperature and get comfort with your building skill, you can design it anyway you like as long as it work!

Well, this is the end of my guide, I hope you like what I wrote, and thank you for your time.
Let's go gaming. :D

I put this topic as an extra because there is noting relate to the temperature rule, but since there are a few people asking about it, so I decide to put it here : )

In this game, there is a thing call stability, which act as a gravity force, so you can't build anything that defy gravity law like floating castle as in Minecraft. Let's see how stability work in the next picture.


Stability rule is simple, it's start with 4, and when it hit 0, the object is destroyed. Once you build any object, it will use the same stability value as the object directly below it where it place. If the object below it is absent, it will use the highest stability value from the object next to it in four direction (north, east, south, west) and minus by 1. If there is still none, this object will not be able to build.

For example, in 1x1 room underground, will cause the wall stability above reduce to 3, because the highest stability value next to it is 4, so, it value is 4 - 1 = 3. With stability 3, you can extend 2 floors from this pillar of wall. And when the underground room keep getting bigger, the less floor can be extend in the sky. Once your underground room is bigger than 7x7, you will start to see that the ground above is collapsed, this is happen because the stability of the dirt above it will be 0.


So, with the stability rule in mind, I usually design my underground cold storage room expand the other way from my building. By doing this, I don't need to worry about my underground room will collapse my castle if I expand too wide. If you didn't plan to create a massive labyrinth underground, and you just need a room to store food, I recommend this method for you.


If, you really want to have an underground room directly below your building, but you are too lazy to design something complicate. I recommend you to create the pile foundation like in real life construction business. Each with 2 blocks away from each other this will guarantee that you will always have enough stability to create floor on top no matter how big your room is and no matter which direction you expand. The downsize for this design is, there will be a lot of pillar in you room and blocking a lot of space for furniture, so you need to be a little bit clever in interior design instead.


The reason why these pile foundation is a recommend method, because it is the best way to sustain stability value. From the above image, you can see that the layout in the middle is very messy to deal with, you barely have any stability enough to build anything in the top floor. That why I recommend to create a pillar in one line as in the left layout. Of course, you can try any other combination that suits your play style. Six is probably the largest space away from one pillar with another, you can create a big room space with this. But don't forget to keep your eye on stability.

In the end, this is only just a guide, you can mix and match my idea with your to create any great structure you wish. Have fun! :D