diff --git a/.luacheckrc b/.luacheckrc
index 334f350dc..ec80df3a0 100644
--- a/.luacheckrc
+++ b/.luacheckrc
@@ -143,6 +143,7 @@ add_ignore("CorsixTH/Lua/app.lua", "212")
 add_ignore("CorsixTH/Lua/calls_dispatcher.lua", "212")
 add_ignore("CorsixTH/Lua/dialogs/bottom_panel.lua", "212")
 add_ignore("CorsixTH/Lua/dialogs/confirm_dialog.lua", "212")
+add_ignore("CorsixTH/Lua/dialogs/edit_room.lua", "113") -- accessing hasBit and bitOr utility.lua functions
 add_ignore("CorsixTH/Lua/dialogs/edit_room.lua", "212")
 add_ignore("CorsixTH/Lua/dialogs/edit_room.lua", "542")
 add_ignore("CorsixTH/Lua/dialogs/fullscreen.lua", "212")
@@ -223,6 +224,7 @@ add_ignore("CorsixTH/Lua/strings.lua", "212")
 add_ignore("CorsixTH/Lua/strings.lua", "122")
 add_ignore("CorsixTH/Lua/ui.lua", "111") -- _ is set in debug code
 add_ignore("CorsixTH/Lua/ui.lua", "212")
+add_ignore("CorsixTH/Lua/utility.lua", "111") -- defining hasBit and bitOr
 add_ignore("CorsixTH/Lua/utility.lua", "121")
 add_ignore("CorsixTH/Lua/window.lua", "212")
 add_ignore("CorsixTH/Lua/window.lua", "542")
diff --git a/CorsixTH/Lua/app.lua b/CorsixTH/Lua/app.lua
index 58597806a..360a89543 100644
--- a/CorsixTH/Lua/app.lua
+++ b/CorsixTH/Lua/app.lua
@@ -28,7 +28,7 @@ local runDebugger = dofile "run_debugger"
 -- Increment each time a savegame break would occur
 -- and add compatibility code in afterLoad functions
 
-local SAVEGAME_VERSION = 118
+local SAVEGAME_VERSION = 119
 
 class "App"
 
diff --git a/CorsixTH/Lua/dialogs/edit_room.lua b/CorsixTH/Lua/dialogs/edit_room.lua
index 3ecf710ed..587161a71 100644
--- a/CorsixTH/Lua/dialogs/edit_room.lua
+++ b/CorsixTH/Lua/dialogs/edit_room.lua
@@ -711,7 +711,13 @@ function UIEditRoom:screenToWall(x, y)
     -- top corner
     local x_, _ = self.ui:WorldToScreen(cellx, celly)
     if x >= x_ then
-      return cellx + 1 + modifier, celly, "north"
+      -- correctly reflects (at least origin version) of TH.
+      -- Swing doors in top corner to the east, actually skip another tile
+      if swinging then
+        return cellx + 2 + modifier, celly, "north"
+      else
+        return cellx + 1 + modifier, celly, "north"
+      end
     else
       return cellx, celly + 1 + modifier, "west"
     end
@@ -727,7 +733,11 @@ function UIEditRoom:screenToWall(x, y)
     -- left corner
     local _, y_ = self.ui:WorldToScreen(cellx, celly)
     if y >= y_ + 16 then
-      return cellx + 1, celly, "south"
+      if swinging and cellx <= rect.x + 2 then
+        return cellx + 1 + modifier, celly, "south"
+      else
+        return cellx + 1, celly, "south"
+      end
     else
       return cellx, celly - 1, "west"
     end
@@ -735,7 +745,11 @@ function UIEditRoom:screenToWall(x, y)
     -- right corner
     local _, y_ = self.ui:WorldToScreen(cellx, celly)
     if y >= y_ + 16 then
-      return cellx, celly + 1, "east"
+      if swinging and celly <= rect.y + 2 then
+        return cellx, celly + 1 + modifier, "east"
+      else
+        return cellx, celly + 1, "east"
+      end
     else
       return cellx - 1, celly, "north"
     end
@@ -752,19 +766,22 @@ function UIEditRoom:screenToWall(x, y)
     return rect.x, celly, "west"
   elseif (celly == rect.y - 1 or celly == rect.y) and rect.x <= cellx and cellx < rect.x + rect.w then
     -- north edge
-    if cellx == rect.x then
-      cellx = rect.x + 1
+    -- correctly reflects (at least origin version) of TH.
+    -- Swing doors in top corner to the east, actually skip another tile
+    if swinging and cellx <= rect.x + 2 then
+      cellx = rect.x + 3
+    elseif cellx == rect.x then
+      cellx = rect.x + 1 + modifier
     elseif cellx == rect.x + rect.w - 1 then
       cellx = rect.x + rect.w - 2
     end
-    if swinging and cellx <= rect.x + 1 then
-      cellx = cellx + 1
-    end
     return cellx, rect.y, "north"
   elseif (cellx == rect.x + rect.w or cellx == rect.x + rect.w - 1) and
       rect.y <= celly and celly < rect.y + rect.h then
-    -- east edge
-    if celly == rect.y then
+      -- east edge
+    if swinging and celly <= rect.y + 1 then
+      celly = rect.y + 2
+    elseif celly == rect.y then
       celly = rect.y + 1
     elseif celly == rect.y + rect.h - 1 then
       celly = rect.y + rect.h - 2
@@ -773,7 +790,9 @@ function UIEditRoom:screenToWall(x, y)
   elseif (celly == rect.y + rect.h or celly == rect.y + rect.h - 1) and
       rect.x <= cellx and cellx < rect.x + rect.w then
     -- south edge
-    if cellx == rect.x then
+    if swinging and cellx <= rect.x + 1 then
+      cellx = rect.x + 2
+    elseif cellx == rect.x then
       cellx = rect.x + 1
     elseif cellx == rect.x + rect.w - 1 then
       cellx = rect.x + rect.w - 2
@@ -1053,11 +1072,20 @@ function UIEditRoom:setBlueprintRect(x, y, w, h)
   rect.h = h
 end
 
+--25 north wall, west
+--26 north wall, east
+--27 east wall, south
+--28 east wall, north
+--29 south wall, west
+--30 south wall, east
+--31 west wall, south
+--32 west wall, north
+-- single door blue print values matching TH
 local door_floor_blueprint_markers = {
-  north = 25,
-  east = 28,
-  south = 29,
-  west = 32,
+  north = 26,
+  east = 27,
+  south = 30,
+  west = 31
 }
 
 local window_floor_blueprint_markers = {
@@ -1071,8 +1099,12 @@ local window_floor_blueprint_markers = {
 --!param x (int) X tile position of the door.
 --!param y (int) Y tile position of the door.
 --!param wall (string) Name of the wall (either 'north' or 'west').
---!param has_swingdoor Whether the room has a normal door (false) or a swing door (true) as entrance.
---!return whether the door can be placed at the given position and orientation.
+--!param has_swingdoor (boolean) Whether the room has a normal door (false) or a swing door (true) as entrance.
+--!return (int) bit flags indicating invalid tile position using 1 based power of 2 as this works with ipairs
+--!  values returned are the enumeration of
+--!  4 = centre door in swing door or for single door the value can just be non-zero but uses the same bit of code
+--!  2 (door section closer to top of screen) - smaller x or y
+--!  8 (door section closer to bottom of screen) - larger x or y
 local function checkDoorWalls(x, y, wall, has_swingdoor)
   local th = TheApp.map.th
 
@@ -1086,42 +1118,51 @@ local function checkDoorWalls(x, y, wall, has_swingdoor)
     dx = 1
     dy = 0
   end
-
+  local invalid_tile = 0
   if th:getCell(x, y, wall_num) % 0x100 ~= 0 then
-    return false
+    invalid_tile = 4
   end
 
   -- If it is a swing door there are two more locations to check.
   if has_swingdoor then
-    if th:getCell(x - dx, y - dy, wall_num) % 0x100 ~= 0 or
-        th:getCell(x + dx, y + dy, wall_num) % 0x100 ~= 0 then
-      return false
+    if th:getCell(x - dx, y - dy, wall_num) % 0x100 ~= 0 then
+      invalid_tile = invalid_tile + 2
+    end
+    if th:getCell(x + dx, y + dy, wall_num) % 0x100 ~= 0 then
+      invalid_tile = invalid_tile + 8
     end
   end
-  return true
+  return invalid_tile
 end
 
 --! Check whether the given tile can function as a door entry/exit tile.
 --!param xpos (int) X position of the tile.
 --!param ypos (int) Y position of the tile.
 --!param player_id (int) Player id owning the hospital.
---!param flag_names (array) If set, array with two additional required properties.
---!return Whether the tile is considered to be valid.
-local function validDoorTile(xpos, ypos, player_id, flag_names)
+--!param world - reference to world object instance
+--!return (boolean) whether the tile is considered to be valid.
+local function validDoorTile(xpos, ypos, player_id, world)
   local th = TheApp.map.th
-
   local tile_flags = th:getCellFlags(xpos, ypos)
-  if not (tile_flags.buildable or tile_flags.passable or tile_flags.owner == player_id) then return false end
-  if not flag_names then return true end
-  return tile_flags[flag_names[1]] and tile_flags[flag_names[2]]
+  -- check own it
+  if tile_flags.owner ~= player_id then return false end
+  -- any object will cause it to be blocked (ignore litter)
+  if tile_flags.thob ~= 0 and tile_flags.thob ~= 62 then return false end
+  -- check if its passable that no object footprint blocks it
+  if tile_flags.passable then return world:isTileExclusivelyPassable(xpos, ypos, 1) end
+  return true
 end
 
-function UIEditRoom:setDoorBlueprint(orig_x, orig_y, orig_wall)
-  local x = orig_x
-  local y = orig_y
-  local wall = orig_wall
-
-  -- Used to get the adjacent tiles when placing swing doors.
+--! Calculate position offsets and door blueprint wall values
+--! param x (int) doors blueprint x value
+--! param y (int) doors blueprint y value
+--! param wall (string) original wall orientation
+--! return x (int) updated x value
+--! return y (int) updated y value
+--! return x_mod (int) offest value to apply to tile count to determine relative position
+--! return y_mod (int) offset value to apply to tile count to determine relatitve position
+--! return wall (string) wall orientation style (only 2 styles)
+local function doorWallOffsetCalculations(x, y, wall)
   local x_mod
   local y_mod
   if wall == "south" then
@@ -1137,11 +1178,20 @@ function UIEditRoom:setDoorBlueprint(orig_x, orig_y, orig_wall)
   else
     y_mod = 2
   end
+  return x, y, x_mod, y_mod, wall
+end
+
+function UIEditRoom:setDoorBlueprint(orig_x, orig_y, orig_wall)
+  local x, y, x_mod, y_mod, wall = doorWallOffsetCalculations(orig_x, orig_y, orig_wall)
   local map = TheApp.map.th
 
   if self.blueprint_door.anim then
     if self.room_type.swing_doors then
       if self.blueprint_door.anim[1] then
+        -- retrieve the old door position details to reset the blue print
+        local oldx, oldy
+		local _, _, oldx_mod, oldy_mod, _ = doorWallOffsetCalculations(self.blueprint_door.floor_x,
+          self.blueprint_door.floor_y, self.blueprint_door.wall)
         -- If we're dealing with swing doors the anim variable is actually a table with three
         -- identical "doors".
         for i, anim in ipairs(self.blueprint_door.anim) do
@@ -1149,8 +1199,10 @@ function UIEditRoom:setDoorBlueprint(orig_x, orig_y, orig_wall)
             self.blueprint_door.old_flags[i])
           anim:setTag(nil)
           self.blueprint_door.anim[i] = nil
+          oldx = oldx_mod and self.blueprint_door.floor_x + (i - oldx_mod) or self.blueprint_door.floor_x
+          oldy = oldy_mod and self.blueprint_door.floor_y + (i - oldy_mod) or self.blueprint_door.floor_y
+          map:setCell(oldx, oldy, 4, 24)
         end
-        map:setCell(self.blueprint_door.floor_x, self.blueprint_door.floor_y, 4, 24)
       end
     else
       self.blueprint_door.anim:setAnimation(self.anims, self.blueprint_door.old_anim,
@@ -1202,49 +1254,59 @@ function UIEditRoom:setDoorBlueprint(orig_x, orig_y, orig_wall)
     flags = 0
     y2 = y2 - 1
   end
-
-  self.blueprint_door.valid = checkDoorWalls(x, y, wall, self.room_type.swing_doors)
-  if self.blueprint_door.valid then
-    -- Ensure that the door isn't being built on top of an object
-    local flag_names
-    if wall == "west" then
-      flag_names = {"buildableNorth", "buildableSouth"}
-    else
-      flag_names = {"buildableWest", "buildableEast"}
-    end
-    local player_id = self.ui.hospital:getPlayerIndex()
-
-    if not validDoorTile(x, y, player_id, flag_names) or
-        not validDoorTile(x2, y2, player_id, flag_names) then
-      self.blueprint_door.valid = false
+  local world = self.ui.app.world
+  -- invalid_tile used to select the individual blueprint that is blocked
+  local invalid_tile = checkDoorWalls(x, y, wall, self.room_type.swing_doors)
+  -- Ensure that the door isn't being built on top of an object
+  local player_id = self.ui.hospital:getPlayerIndex()
+  if not validDoorTile(x, y, player_id, world) or
+      not validDoorTile(x2, y2, player_id, world) then
+    invalid_tile = bitOr(invalid_tile, 4)
+  end
+  -- If we're making swing doors two more tiles need to be checked.
+  if self.room_type.swing_doors then
+    local dx = x_mod and 1 or 0
+    local dy = y_mod and 1 or 0
+    if not validDoorTile(x + dx, y + dy, player_id, world) or
+        not validDoorTile(x2 + dx, y2 + dy, player_id, world) then
+      invalid_tile = bitOr(invalid_tile, 8)
     end
-    -- If we're making swing doors two more tiles need to be checked.
-    if self.room_type.swing_doors then
-      local dx = x_mod and 1 or 0
-      local dy = y_mod and 1 or 0
-      if not validDoorTile(x + dx, y + dy, player_id, nil) or
-          not validDoorTile(x2 + dx, y2 + dy, player_id, nil) then
-        self.blueprint_door.valid = false
-      end
-      if not validDoorTile(x - dx, y - dy, player_id, nil) or
-          not validDoorTile(x2 - dx, y2 - dy, player_id, nil) then
-        self.blueprint_door.valid = false
-      end
+    if not validDoorTile(x - dx, y - dy, player_id, world) or
+        not validDoorTile(x2 - dx, y2 - dy, player_id, world) then
+      invalid_tile = bitOr(invalid_tile, 2)
     end
   end
-  if not self.blueprint_door.valid then
-    flags = flags + 16 -- Use red palette rather than normal palette
-  end
+
+  self.blueprint_door.valid = (invalid_tile == 0)
+
   if self.room_type.swing_doors then
-    for _, animation in ipairs(anim) do
-      animation:setAnimation(self.anims, 126, flags)
+    for i, animation in ipairs(anim) do
+      -- calculation here to flag blocked blueprint tiles on swing doors for each door tile
+      animation:setAnimation(self.anims, 126, flags + (hasBit(invalid_tile, i) and 1 or 0) * 16)
     end
   else
-    anim:setAnimation(self.anims, 126, flags)
+    anim:setAnimation(self.anims, 126, flags + (invalid_tile ~= 0 and 1 or 0) * 16)
   end
-  if self.blueprint_door.valid then
+  if self.room_type.swing_doors then
+    flags = door_floor_blueprint_markers[orig_wall]
+    local dirfix = orig_wall == "east"
+    flags = dirfix and flags + 1 or flags
+    for i = 1, 3 do
+      local x1 = x_mod and orig_x + i - x_mod or orig_x
+      local y1 = y_mod and orig_y + i - y_mod or orig_y
+      if (i == 2) then
+        map:setCell(x1, y1, 4, 24)
+      else
+        if dirfix then
+          map:setCell(x1, y1, 4, i < 2 and flags or flags - 1)
+        else
+          map:setCell(x1, y1, 4, i > 2 and flags or flags - 1)
+        end
+      end
+    end
+  else
     map:setCell(self.blueprint_door.floor_x, self.blueprint_door.floor_y, 4,
-        door_floor_blueprint_markers[orig_wall])
+      door_floor_blueprint_markers[orig_wall])
   end
 end
 
diff --git a/CorsixTH/Lua/dialogs/place_objects.lua b/CorsixTH/Lua/dialogs/place_objects.lua
index 67f5d7f1a..158024e1b 100644
--- a/CorsixTH/Lua/dialogs/place_objects.lua
+++ b/CorsixTH/Lua/dialogs/place_objects.lua
@@ -657,11 +657,18 @@ function UIPlaceObjects:setBlueprintCell(x, y)
 
         -- Check 3: The footprint tile should either be buildable or passable, is it?:
         if not tile.only_side and is_object_allowed then
-           is_object_allowed = world:isFootprintTileBuildableOrPassable(xpos, ypos, tile, object_footprint, flag, player_id)
+          is_object_allowed = world:isFootprintTileBuildableOrPassable(xpos, ypos, tile, object_footprint, flag, player_id)
         elseif is_object_allowed then
           is_object_allowed = map:getCellFlags(xpos, ypos, flags)[flag] and (player_id == 0 or flags.owner == player_id)
         end
 
+        -- ignore placed object tile if it is shareable
+        if not tile.shareable and is_object_allowed then
+          -- Check 4: only one object per tile allowed original TH
+          -- can build on litter and unoccupied tiles and only placeable if not on another objects passable footprint unless that too is a shareable tile
+          is_object_allowed = world:isTileExclusivelyPassable(xpos, ypos, 10)
+        end
+
         -- Having checked if the tile is good set its blueprint appearance flag:
         if is_object_allowed then
           if not tile.invisible then
diff --git a/CorsixTH/Lua/objects/bench.lua b/CorsixTH/Lua/objects/bench.lua
index 8b1b044a8..c617a8b4a 100644
--- a/CorsixTH/Lua/objects/bench.lua
+++ b/CorsixTH/Lua/objects/bench.lua
@@ -126,19 +126,19 @@ object.usage_animations = {
 object.orientations = {
   north = {
     render_attach_position = { {0, 0}, {-1, 0}, {0, -1} },
-    footprint = { {0, 0, complete_cell = true}, {0, -1, only_passable = true, invisible = true} },
+    footprint = { {0, 0, complete_cell = true}, {0, -1, only_passable = true, invisible = true, shareable = true} },
     use_position = "passable",
   },
   east = {
-    footprint = { {0, 0, complete_cell = true}, {1, 0, only_passable = true, invisible = true} },
+    footprint = { {0, 0, complete_cell = true}, {1, 0, only_passable = true, invisible = true, shareable = true} },
     use_position = "passable",
   },
   south = {
-    footprint = { {0, 0, complete_cell = true}, {0, 1, only_passable = true, invisible = true} },
+    footprint = { {0, 0, complete_cell = true}, {0, 1, only_passable = true, invisible = true, shareable = true} },
     use_position = "passable",
   },
   west = {
-    footprint = { {0, 0, complete_cell = true}, {-1, 0, only_passable = true, invisible = true} },
+    footprint = { {0, 0, complete_cell = true}, {-1, 0, only_passable = true, invisible = true, shareable = true} },
     use_position = "passable",
   },
 }
@@ -194,4 +194,12 @@ function Bench:onDestroy()
   Object.onDestroy(self)
 end
 
+--! This function is automatically called after loading a game and serves for compatibility.
+function Bench:afterLoad(old, new)
+  if old < 119 then
+    self.footprint = object.orientations[self.direction].footprint
+  end
+  Object.afterLoad(self, old, new)
+end
+
 return object
diff --git a/CorsixTH/Lua/objects/chair.lua b/CorsixTH/Lua/objects/chair.lua
index 53f7540d7..dc20874cc 100644
--- a/CorsixTH/Lua/objects/chair.lua
+++ b/CorsixTH/Lua/objects/chair.lua
@@ -136,21 +136,38 @@ object.usage_animations = {
 }
 object.orientations = {
   north = {
-    footprint = { {0, 0, complete_cell = true}, {0, -1, only_passable = true} },
+    footprint = { {0, 0, complete_cell = true}, {0, -1, only_passable = true, invisible = true, shareable = true} },
     use_position = "passable",
   },
   east = {
-    footprint = { {0, 0, complete_cell = true}, {1, 0, only_passable = true} },
+    footprint = { {0, 0, complete_cell = true}, {1, 0, only_passable = true, invisible = true,  shareable = true} },
     use_position = "passable",
   },
   south = {
-    footprint = { {0, 0, complete_cell = true}, {0, 1, only_passable = true} },
+    footprint = { {0, 0, complete_cell = true}, {0, 1, only_passable = true, invisible = true,  shareable = true} },
     use_position = "passable",
   },
   west = {
-    footprint = { {0, 0, complete_cell = true}, {-1, 0, only_passable = true} },
+    footprint = { {0, 0, complete_cell = true}, {-1, 0, only_passable = true, invisible = true,  shareable = true} },
     use_position = "passable",
   },
 }
 
+class "Chair" (Object)
+
+---@type Chair
+local Chair = _G["Chair"]
+
+function Chair:Chair(...)
+  self:Object(...)
+end
+
+--! This function is automatically called after loading a game and serves for compatibility.
+function Chair:afterLoad(old, new)
+  if old < 119 then
+    self.footprint = object.orientations[self.direction].footprint
+  end
+  Object.afterLoad(self, old, new)
+end
+
 return object
diff --git a/CorsixTH/Lua/utility.lua b/CorsixTH/Lua/utility.lua
index 3bedfaf1b..281c18fdb 100644
--- a/CorsixTH/Lua/utility.lua
+++ b/CorsixTH/Lua/utility.lua
@@ -293,3 +293,22 @@ function rangeMapLookup(number, buckets)
   end
   assert(false) -- Should never get here.
 end
+
+-- this is a pseudo bitwise OR operation
+-- assumes value2 is always a power of 2 (limits carry errors in the addition)
+-- mimics the logic of hasBit with the addition if bit not set
+--!param value1 (int) value to check set bit of
+--!param value2 (int) power of 2 value - bit enumeration
+--!return (int) value1 and value2 'bitwise' or.
+function bitOr(value1, value2)
+  return value1 % (value2 + value2) >= value2 and value1 or value1 + value2
+end
+
+--! Check bit is set
+--!param value (int) value to check set bit of
+--!param bit (int) 0-base index of bit to check
+--!return (boolean) true if bit is set.
+function hasBit(value, bit)
+  local p = 2 ^ bit
+  return value % (p + p) >= p
+end
diff --git a/CorsixTH/Lua/world.lua b/CorsixTH/Lua/world.lua
index a1ab8fe6e..23e735529 100644
--- a/CorsixTH/Lua/world.lua
+++ b/CorsixTH/Lua/world.lua
@@ -2697,3 +2697,32 @@ function World:resetSideObjects()
     end
   end
 end
+
+--[[ When placing doors and objects the passable tiles need to be checked for overlapping
+passable tiles. This presents problems with objects like Bench where the passable tile
+is not for exclusive use of the Bench (another object can share that same tile)
+the footprint.shareable differentiates shareable passable tiles, and exclusive use
+passable tiles (the norm for most objects)]]
+--!param x (int) x map tile position
+--!param y (int) y map tile position
+--!param distance (int) searchable distance for nearby objects
+--!return (boolean) indicating if exclusively passable or not
+function World:isTileExclusivelyPassable(x, y, distance)
+  for o in pairs(self:findAllObjectsNear(x, y, distance)) do
+    if o and o.footprint then
+      for _, footprint in pairs(o.footprint) do
+        if footprint[1] + o.tile_x == x and footprint[2] + o.tile_y == y and footprint.only_passable and not footprint.shareable then
+          return false
+        end
+      end
+    else
+      -- doors don't have a footprint but objects can't be built blocking them either
+      for _, footprint in pairs(o:getWalkableTiles()) do
+        if o.object_type and o.object_type.thob ~= 62 and footprint[1] == x and footprint[2] == y then
+          return false
+        end
+      end
+    end
+  end
+  return true
+end