In Rise of Nations, damaged buildings can be repaired by Citizens. The Citizen must be next to a building to repair it, and if the building is under attack, the Citizen will also take some damage. Repairing a building takes some resources, and multiple Citizens can repair a building at the same time.
Building Repair Rate Edit
Standard Repair Rate Edit
The rate at which a Citizen will repair a building is generally half the rate at which it takes to build the building. For example, if a building takes 10 seconds for a single Citizen to construct, it will take 20 seconds for a single Citizen to repair the building from 0 hit points to full hit points. Like building construction, multiple Citizens can repair a building at once, to speed up repairs. However, the 2nd Citizen is only 1/2 as effective as a single Citizen, the 3rd Citizen is only 1/3 as effective, the 4th Citizen is only 1/4 as effective, and so on, with the nth Citizen contributing 1/n of the regular repair rate. Thus, the repair rate (with "1" being the rate of a single Citizen for a given building), for different numbers of Citizens, is:
|Number of Citizens||Repair Rate||Repair Time (%)|
The rate of repair is constant based on the building's build time, and as a percentage of its total hit points. Thus, as a building's total hit points increase during the course of a game, the rate of repair in terms of hit points per second will increase, even though the rate of repair as a percentage of the total hit points stays constant.
For example, a Fort has 2000 hit points (assuming no bonuses), and takes 133.3 seconds (2000 frames) to build. The repair rate then is 2000 / 133.3 / 2 = 7.5 hit points per second (0.5 hit points per frame). A Redoubt has 4600 hit points (assuming no bonuses), and takes 133.3 seconds (2000 frames) to build. The repair rate then is 4600 / 133.3 / 2 = 17.25 hit points per second (1.15 hit points per frame). Thus, by researching Ages and receiving the automatic building upgrades from Fort to Redoubt, the repair rate (in terms of hit points per second) is automatically increased. If there are 3 Citizens repairing the Redoubt, then the repair rate would be 4600 / 133.3 / 2 * 1.833 = 31.6 hit points per second (2.1 hit points per frame).
Korean Repair Rate Edit
The Koreans' nation power is described as repairing 50% faster. However, the effect is actually to decrease the time needed to repair a building by 50%, so the repair rate is actually twice the standard rate. This rate also applies to if a Korean Citizen repairs an ally's building. Because each additional Citizen is less effective at repairing, a Korean Citizen repairing, at twice the standard rate, is about equivalent to 4 regular Citizens repairing. Two Korean Citizens repairing, at 3X the standard rate, is about equivalent to 11 regular Citizens repairing. Three Korean Citizens repairing, at 3.67X the standard rate, is about equivalent to 21 regular Citizens repairing. Four Korean Citizens repairing, at 4.17X the standard rate, is about equivalent to 36 regular Citizens repairing. Thus, the Koreans need relatively few Citizens to repair rapidly. This, combined with the Korean Citizen ability to repair without being damaged by attacks on the building, means that Koreans have a strong defensive repairing ability against attacks. Although generally not relevant, doubling the rate of repair means that the rate of resource consumption when repairing is also doubled.
Starting City Repair Rate Edit
The rate of repair at a starting city (the initial city of each nation) is only 1/3 of the standard rate of repair. This is because the starting city has a 3X build time (set in rules.xml as CAPITAL_BUILD_TIME). This reduced rate of repair is permanent for that city even if the nation's capital is moved to another city and/or if the starting city is captured by another nation. A single Citizen repairing a starting city during assimilation will repair only around 163 hit points before it is assimilated, while the Citizen will repair close to 500 hit points for a regular city during the same amount of time.
Building Repair Cost Edit
Repairing a building takes resources, withdrawn gradually as the building is repaired. The cost to repair a building from 0 hit points to full hit points is generally the cost to build an additional one of the same type of building. For example, if a nation already has 4 Forts, the 5th Fort would cost 900 Metal and 300 Wealth. Thus, the cost to repair any of the existing 4 Forts from 0 hit points to full hit points would be 900 Metal and 300 Wealth. The number of buildings includes buildings that have been placed even if they have not begun construction, and is updated continually as a building is being repaired, so the cost of repairs may fluctuate if other buildings are being destroyed or being placed or built.
This cost is static even as the building's hit points is increased. Thus, even though the total cost to repair the building stays the same, the cost to repair a given amount of hit points will decrease as the building's total hit points increases during the course of a game.
If a nation has nation powers that decrease the cost of a building, such as the Romans and Forts, this is reflected in the cost of repairing that building.
Other Sources of Repair Edit
The consensus Patriots The Senator, The President, and The CEO will heal buildings in their radius, at the rate of 0.75 hit points per second. This is free, and is thus a way to repair a building without using resources.
When not under attack, Small Cities will automatically heal at the rate of 3.75 hit points per second (1 every 4 frames), Large Cities will automatically heal at the rate of 7.5 hit points per second (2 every 4 frames), and Major Cities will automatically heal at the rate of 11.25 hit points per second (3 every 4 frames).
When a building is upgraded and its hit points is increased, the difference in total hit points is added to the building's current hit points. An extended conclusion is, it is possible to immediately recover part of your city's hit points by razing and rebuilding the temple in that city(4+ citizens is necessary) repeatedly. This could be helpful in defense.