When to repair buildings? Do it at 45 days, not 90 days in the FAQ

Hello PrUn citizens!

The official FAQ says
“Many in the community suggest repairing at around 90 days.”
But after some analysis, this advice could be better.

The knowledge is out there but not clearly shown, so here is my take on building repair by heat mapping the material cost vs efficiency to show the total lost production days vs the age of the building. It is pretty clear from this that at 45 days you use material at the same rate as if you waited til 90 days, but you gain 2 to 3.5 full days of production doing two 45 day repairs vs one 90 day repair. See for yourself!

I recommend updating the official FAQ:

Thanks for reading!

-Your friends at Canadian Tire & Ammo [CTIR]
PS. Special thanks to our partners at Ascaron [ASCA] for the inspiration!


This is a great analysis, I never thought of it that way before.

However, where it gets difficult is where you have a building with, say, 4x BSE and 3x BBH. Now whenever you repair you’re going to be “wasting” some materials, but since BBH is more expensive than BSE then it’s better to align with the BBH, hence 60 days would be the best time.

Given the complexity in practice, I’m not sure that the official FAQ needs updating. The advice as written is not bad for a beginner, and it is difficult to come up with a simple rule that applies well to any building.

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Opportunity cost matters. Personally I agree that 90d tends to be worse than earlier dates, but for newer players with very high rates of return this is likely different. (Edit: Technically the earlier the better. For example an EXT, for optimal results, should get repaired every 11.25 days, not every 45 days.)

A base full of low-tier buildings costs like 2k/d in degradation. What is the opportunity cost in repairing for 90k after 45 days vs for 180k after 90d? Those extra 90k you pay much later can get you 2 or 3 production buildings each producing 2-3k/d. Yes, I’m assuming same efficiency for both repair dates, but the difference is so stark it easily offsets the meager savings of 3.5 production days over 45 days. Say, conservatively, you get 2 extra production buildings for that money, that’s 90 production days added over those 45 days you wait, right?


This wouldn’t hold true for my one water planet that requires TSH and HSE, where 90D is 35 units each or it would be 70 units if i did it at 45d

Even at 3.5 days production that is far below the extra cost of TSH/HSE

35 TSH is 1,330,000
35 HSE is 448,400

3.5 days of extra water is 10153 units or 355,372.5

  • all prices calculated off MOR CX Average.

That said simple places like Montem i agree 90 is not the best, cheaper planets i tend to do more often ~30 days but places that use HSE or TSH or even worse both yeah not a chance that’s a 85-90 day redo.