5 files changed, 38 insertions, 13 deletions
diff --git a/src/date.cpp b/src/date.cpp
index d477b7359..4b4b94bb0 100644
--- a/src/date.cpp
+++ b/src/date.cpp
@@ -171,6 +171,7 @@ extern void TrainsYearlyLoop();
 extern void RoadVehiclesYearlyLoop();
 extern void AircraftYearlyLoop();
 extern void ShipsYearlyLoop();
+extern void TownsYearlyLoop();
 
 extern void ShowEndGameChart();
 
@@ -275,6 +276,7 @@ void IncreaseDate()
 	RoadVehiclesYearlyLoop();
 	AircraftYearlyLoop();
 	ShipsYearlyLoop();
+	TownsYearlyLoop();
 #ifdef ENABLE_NETWORK
 	if (_network_server) NetworkServerYearlyLoop();
 #endif /* ENABLE_NETWORK */
diff --git a/src/newgrf_house.cpp b/src/newgrf_house.cpp
index f112936f0..ce7558f97 100644
--- a/src/newgrf_house.cpp
+++ b/src/newgrf_house.cpp
@@ -316,7 +316,7 @@ static uint32 HouseGetVariable(const ResolverObject *object, byte variable, byte
 		case 0x40: return (IsTileType(tile, MP_HOUSE) ? GetHouseBuildingStage(tile) : 0) | TileHash2Bit(TileX(tile), TileY(tile)) << 2;
 
 		/* Building age. */
-		case 0x41: return Clamp(_cur_year - GetHouseConstructionYear(tile), 0, 0xFF);
+		case 0x41: return GetHouseAge(tile);
 
 		/* Town zone */
 		case 0x42: return GetTownRadiusGroup(town, tile);
diff --git a/src/openttd.cpp b/src/openttd.cpp
index c79b68014..c4c39cf9a 100644
--- a/src/openttd.cpp
+++ b/src/openttd.cpp
@@ -2477,8 +2477,8 @@ bool AfterLoadGame()
 	}
 
 	if (CheckSavegameVersion(99)) {
-		/* Set newly introduced WaterClass of industry tiles */
 		for (TileIndex t = 0; t < map_size; t++) {
+			/* Set newly introduced WaterClass of industry tiles */
 			if (IsTileType(t, MP_STATION) && IsOilRig(t)) {
 				SetWaterClassDependingOnSurroundings(t, true);
 			}
@@ -2489,6 +2489,11 @@ bool AfterLoadGame()
 					SetWaterClass(t, WATER_CLASS_INVALID);
 				}
 			}
+
+			/* Replace "house construction year" with "house age" */
+			if (IsTileType(t, MP_HOUSE) && IsHouseCompleted(t)) {
+				_m[t].m5 = Clamp(_cur_year - (_m[t].m5 + ORIGINAL_BASE_YEAR), 0, 0xFF);
+			}
 		}
 	}
 
diff --git a/src/town_cmd.cpp b/src/town_cmd.cpp
index a2411f7ce..19cc2ec05 100644
--- a/src/town_cmd.cpp
+++ b/src/town_cmd.cpp
@@ -404,7 +404,7 @@ static void MakeSingleHouseBigger(TileIndex tile)
 		/* Now that construction is complete, we can add the population of the
 		 * building to the town. */
 		ChangePopulation(GetTownByTile(tile), hs->population);
-		SetHouseConstructionYear(tile, _cur_year);
+		ResetHouseAge(tile);
 	}
 	MarkTileDirtyByTile(tile);
 }
@@ -505,7 +505,7 @@ static void TileLoop_Town(TileIndex tile)
 	if (hs->building_flags & BUILDING_HAS_1_TILE &&
 			HasBit(t->flags12, TOWN_IS_FUNDED) &&
 			CanDeleteHouse(tile) &&
-			max(_cur_year - GetHouseConstructionYear(tile), 0) >= hs->minimum_life &&
+			GetHouseAge(tile) >= hs->minimum_life &&
 			--t->time_until_rebuild == 0) {
 		t->time_until_rebuild = GB(r, 16, 8) + 192;
 
@@ -2608,6 +2608,15 @@ void TownsMonthlyLoop()
 	}
 }
 
+void TownsYearlyLoop()
+{
+	/* Increment house ages */
+	for (TileIndex t = 0; t < MapSize(); t++) {
+		if (!IsTileType(t, MP_HOUSE)) continue;
+		IncrementHouseAge(t);
+	}
+}
+
 void InitializeTowns()
 {
 	/* Clean the town pool and create 1 block in it */
diff --git a/src/town_map.h b/src/town_map.h
index e5f55c12b..b0653a1cd 100644
--- a/src/town_map.h
+++ b/src/town_map.h
@@ -6,8 +6,6 @@
 #define TOWN_MAP_H
 
 #include "town.h"
-#include "date_type.h"
-#include "date_func.h"
 #include "tile_map.h"
 
 /**
@@ -266,27 +264,38 @@ static inline void IncHouseConstructionTick(TileIndex t)
 }
 
 /**
- * Set the year that this house was constructed.
+ * Sets the age of the house to zero.
+ * Needs to be called after the house is completed. During construction stages the map space is used otherwise.
  * @param t the tile of this house
- * @param year the year to set
  * @pre IsTileType(t, MP_HOUSE) && IsHouseCompleted(t)
  */
-static inline void SetHouseConstructionYear(TileIndex t, Year year)
+static inline void ResetHouseAge(TileIndex t)
 {
 	assert(IsTileType(t, MP_HOUSE) && IsHouseCompleted(t));
-	_m[t].m5 = Clamp(year - GetHouseSpecs(GetHouseType(t))->min_year, 0, 0xFF);
+	_m[t].m5 = 0;
 }
 
 /**
- * Get the year that this house was constructed.
+ * Increments the age of the house.
+ * @param t the tile of this house
+ * @pre IsTileType(t, MP_HOUSE)
+ */
+static inline void IncrementHouseAge(TileIndex t)
+{
+	assert(IsTileType(t, MP_HOUSE));
+	if (IsHouseCompleted(t) && _m[t].m5 < 0xFF) _m[t].m5++;
+}
+
+/**
+ * Get the age of the house
  * @param t the tile of this house
  * @pre IsTileType(t, MP_HOUSE)
  * @return year
  */
-static inline Year GetHouseConstructionYear(TileIndex t)
+static inline Year GetHouseAge(TileIndex t)
 {
 	assert(IsTileType(t, MP_HOUSE));
-	return IsHouseCompleted(t) ? _m[t].m5 + GetHouseSpecs(GetHouseType(t))->min_year : _cur_year;
+	return IsHouseCompleted(t) ? _m[t].m5 : 0;
 }
 
 /**