diff --git a/src/main/java/org/kapelle/multiblock/MultiblockStructure.java b/src/main/java/org/kapelle/multiblock/MultiblockStructure.java
index fba5f1e..16a2033 100644
--- a/src/main/java/org/kapelle/multiblock/MultiblockStructure.java
+++ b/src/main/java/org/kapelle/multiblock/MultiblockStructure.java
@@ -3,7 +3,10 @@ package org.kapelle.multiblock;
 import org.bukkit.Location;
 import org.bukkit.util.BlockVector;
 import org.kapelle.multiblock.block_component.IBlockComponent;
+import org.kapelle.multiblock.block_component.ICheckFunction;
+import org.kapelle.multiblock.constraint.IConstraint;
 
+import java.util.ArrayList;
 import java.util.List;
 
 /**
@@ -12,7 +15,8 @@ import java.util.List;
  */
 public class MultiblockStructure {
 
-    List<List<List<IBlockComponent>>> structure;
+    private final List<List<List<IBlockComponent>>> structure;
+    private final List<IConstraint> constraints = new ArrayList<>();
 
     /**
      * Create a multiblock structure.
@@ -32,6 +36,10 @@ public class MultiblockStructure {
         return structure.get(y).get(z).get(x);
     }
 
+    public Location getBlockLocation(Location location, BlockVector offset, BlockVector localPosition){
+        return location.clone().subtract(offset).add(localPosition);
+    }
+
     /**
      * Checks if the multiblock is valid at the given location.
      * @param location Location of a block in a multiblock structure.
@@ -44,7 +52,7 @@ public class MultiblockStructure {
                 for (int x = 0; x < structure.get(y).get(z).size() ; x++) {
 
                     IBlockComponent currentComponent = getComponent(x,y,z);
-                    Location globalBlockLocation = location.clone().subtract(offset).add(new BlockVector(x,y,z));
+                    Location globalBlockLocation = getBlockLocation(location,offset,new BlockVector(x,y,z));
 
                     if(!currentComponent.isValidBlock(globalBlockLocation)){
                         return false;
@@ -53,6 +61,17 @@ public class MultiblockStructure {
             }
         }
 
+        for (IConstraint constraint:constraints) {
+            if(!constraint.isValid(location,offset,this)){
+                return false;
+            }
+        }
+
         return true;
     }
+
+    public void addConstraint(IConstraint constraint){
+        this.constraints.add(constraint);
+    }
+
 }
diff --git a/src/main/java/org/kapelle/multiblock/constraint/IConstraint.java b/src/main/java/org/kapelle/multiblock/constraint/IConstraint.java
new file mode 100644
index 0000000..c6a6d31
--- /dev/null
+++ b/src/main/java/org/kapelle/multiblock/constraint/IConstraint.java
@@ -0,0 +1,9 @@
+package org.kapelle.multiblock.constraint;
+
+import org.bukkit.Location;
+import org.bukkit.util.BlockVector;
+import org.kapelle.multiblock.MultiblockStructure;
+
+public interface IConstraint {
+    public boolean isValid(Location coreBlockLocation, BlockVector offset, MultiblockStructure structure);
+}
diff --git a/src/main/java/org/kapelle/multiblock/constraint/SameBlockConstraint.java b/src/main/java/org/kapelle/multiblock/constraint/SameBlockConstraint.java
new file mode 100644
index 0000000..38d4398
--- /dev/null
+++ b/src/main/java/org/kapelle/multiblock/constraint/SameBlockConstraint.java
@@ -0,0 +1,34 @@
+package org.kapelle.multiblock.constraint;
+
+import org.bukkit.Location;
+import org.bukkit.Material;
+import org.bukkit.util.BlockVector;
+import org.kapelle.multiblock.MultiblockStructure;
+
+import java.security.InvalidParameterException;
+import java.util.List;
+
+public class SameBlockConstraint implements IConstraint{
+
+    private final List<BlockVector> positions;
+
+    public SameBlockConstraint(List<BlockVector> positions){
+        this.positions = positions;
+        if (positions.size() <= 1){
+            throw new InvalidParameterException("position need at least 2 positions");
+        }
+    }
+
+    @Override
+    public boolean isValid(Location coreBlockLocation, BlockVector offset, MultiblockStructure structure) {
+        Material material = structure.getBlockLocation(coreBlockLocation,offset,positions.get(0)).getBlock().getType();
+
+        for (BlockVector pos : positions) {
+            if(structure.getBlockLocation(coreBlockLocation,offset,pos).getBlock().getType() != material){
+                return false;
+            }
+        }
+
+        return true;
+    }
+}