Train troops while upgrading: parallel building tasks in Doomsday
Can you upgrade busy Barracks, a Hospital or a Research Lab? Read IGG's rule, the order of actions and an example that finishes construction six hours earlier.
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Your Barracks still have hours of troop training left, but you already have the resources to upgrade the building. Do not assume you must wait for training to finish. In Doomsday: Last Survivors, the developers enabled upgrades to busy Barracks, the Hospital and Research Lab. The useful questions are which actions can overlap and in what order.
Start the task, then upgrade the building
In IGG's official App Store version history, version 1.53.0 of 13 January 2026 lists three combinations: upgrading the Hospital while healing wounded troops, Barracks while training troops and Research Lab while researching technology. This is an existing rule, not news about a fresh update.
Plan around two distinct processes: the building gains a level while its already-started task continues. Busy Barracks alone need not be a reason to wait for an empty queue before upgrading them. Check your own upgrade window for the other requirements, resources and construction availability.
The order matters. IGG confirms the scenario task already running → start the building upgrade. This does not automatically establish the reverse: building already upgrading → start any new task. If your batch finishes before construction, check whether another batch can start in your client. Do not plan an uninterrupted chain of new batches from this patch sentence alone.
How waiting can cost an evening
Imagine a hypothetical evening: training has six hours left and a Barracks upgrade takes eight hours. You already have the resources and can start construction. Waiting for the troops before upgrading makes the building ready in 6 + 8 = 14 hours. Starting now lets the eight-hour construction timer overlap with the remaining training.
In this example, the building is ready six hours earlier. That saving comes from overlapping the tasks; construction itself still takes eight hours. These are hypothetical timers without speedups or changed bonuses, not a promise of the same saving for every account.
There is a simple counterexample. If you lack the resources for the upgrade, permission to overlap tasks does not start construction for you. Before spending speedups merely to free the Barracks, open the upgrade window and see what actually prevents it: ongoing work, missing materials or another unmet requirement. Address the problem you find.
Be clear about what you are upgrading
In the archived Doomsday Diary frame published on 14 April 2025, the top mission asks for Ranged Barracks level five. The building itself is the mission target. The frame helps distinguish buildings from troops; it predates the update discussed here and does not prove simultaneous construction and training.
Open the game frame at full size
Troops have a separate tier upgrade, while technologies have their own research. Saying I pressed upgrade does not distinguish those actions. When choosing between new soldiers and promoting existing ones to a higher tier, see our training and troop upgrading guide. The question here is when to start upgrading the building.
Plan the start before confirming
In the same update, IGG removed the Cancel option for building, Technology and Biochemical Beast Technology upgrades, explaining it as protection against accidental cancellations. That list cannot be extended to every action in the game. Still, I will cancel it later if I change my mind is a poor basis for starting construction.
Before confirming, choose the building and level, then check the price and completion time. Compare them with the task already running and your next game objective. The useful habit is to check whether tasks can overlap before spending speedups. Sometimes starting construction earlier removes several hours of waiting.
