diff --git a/src/main/java/world/bentobox/greenhouses/greenhouse/Walls.java b/src/main/java/world/bentobox/greenhouses/greenhouse/Walls.java
index d371272..d4a0890 100644
--- a/src/main/java/world/bentobox/greenhouses/greenhouse/Walls.java
+++ b/src/main/java/world/bentobox/greenhouses/greenhouse/Walls.java
@@ -69,7 +69,7 @@ public class Walls extends MinMaxXZ {
         // The player is under the roof
         // Assume the player is inside the greenhouse they are trying to create
         final Location loc = roof.getLocation();
-        floor = getFloorY(roof.getHeight(), roof.getMinX(), roof.getMaxX(), roof.getMinZ(), roof.getMaxZ());
+        floor = getFloorY(roof.getHeight(), roof.getMinX(), roof.getMaxX(), roof.getMinZ(), roof.getMaxZ(), loc.getWorld().getMinHeight());
         // Now start with the player's x and z location
         WallFinder wf = new WallFinder();
         minX = loc.getBlockX();
@@ -85,7 +85,7 @@ public class Walls extends MinMaxXZ {
         minZ--;
         maxZ++;
         // Find the floor again, only looking within the walls
-        floor = getFloorY(roof.getHeight(), minX, maxX, minZ,maxZ);
+        floor = getFloorY(roof.getHeight(), minX, maxX, minZ,maxZ,loc.getWorld().getMinHeight());
         // Complete on main thread
         Bukkit.getScheduler().runTask(BentoBox.getInstance(), () -> r.complete(this));
         return this;
@@ -159,7 +159,7 @@ public class Walls extends MinMaxXZ {
         }
     }
 
-    int getFloorY(int y, int minX, int maxX, int minZ, int maxZ) {
+    int getFloorY(int y, int minX, int maxX, int minZ, int maxZ, int minY) {
         // Find the floor - defined as the last y under the roof where there are no wall blocks
         int wallBlockCount;
         do {
@@ -172,7 +172,7 @@ public class Walls extends MinMaxXZ {
                 }
             }
 
-        } while( y-- > 0 && wallBlockCount > 0);
+        } while( y-- > minY && wallBlockCount > 0);
         return y + 1;
 
     }
diff --git a/src/test/java/world/bentobox/greenhouses/greenhouse/WallsTest.java b/src/test/java/world/bentobox/greenhouses/greenhouse/WallsTest.java
index 29821e1..7231f34 100644
--- a/src/test/java/world/bentobox/greenhouses/greenhouse/WallsTest.java
+++ b/src/test/java/world/bentobox/greenhouses/greenhouse/WallsTest.java
@@ -177,15 +177,15 @@ public class WallsTest {
     }
 
     /**
-     * Test method for {@link world.bentobox.greenhouses.greenhouse.Walls#getFloorY(int, int, int, int, int)}.
+     * Test method for {@link world.bentobox.greenhouses.greenhouse.Walls#getFloorY(int, int, int, int, int, int)}.
      */
     @Test
     public void testGetFloorYZeroY() {
-        assertEquals(0, walls.getFloorY(10, 0, 1, 0, 1));
+        assertEquals(-64, walls.getFloorY(10, 0, 1, 0, 1, -64));
     }
 
     /**
-     * Test method for {@link world.bentobox.greenhouses.greenhouse.Walls#getFloorY(int, int, int, int, int)}.
+     * Test method for {@link world.bentobox.greenhouses.greenhouse.Walls#getFloorY(int, int, int, int, int, int)}.
      */
     @Test
     public void testGetFloorY() {
@@ -193,7 +193,7 @@ public class WallsTest {
                 Material.GLASS, Material.GLASS,
                 Material.GLASS, Material.GLASS,
                 Material.AIR);
-        assertEquals(8, walls.getFloorY(10, 0, 1, 0, 1));
+        assertEquals(8, walls.getFloorY(10, 0, 1, 0, 1, -64));
     }
 
     /**