diff --git a/android/src/mindustry/android/AndroidLauncher.java b/android/src/mindustry/android/AndroidLauncher.java
index 7996c2c93a..4d41e46cb4 100644
--- a/android/src/mindustry/android/AndroidLauncher.java
+++ b/android/src/mindustry/android/AndroidLauncher.java
@@ -1,6 +1,7 @@
 package mindustry.android;
 
 import android.*;
+import android.annotation.*;
 import android.app.*;
 import android.content.*;
 import android.content.pm.*;
diff --git a/core/assets/bundles/bundle.properties b/core/assets/bundles/bundle.properties
index bb93af6d68..d50a74c04f 100644
--- a/core/assets/bundles/bundle.properties
+++ b/core/assets/bundles/bundle.properties
@@ -538,6 +538,7 @@ settings.clearall.confirm = [scarlet]WARNING![]\nThis will clear all data, inclu
 paused = [accent]< Paused >
 clear = Clear
 banned = [scarlet]Banned
+unplaceable.sectorcaptured = [scarlet]Requires captured sector
 yes = Yes
 no = No
 info.title = Info
diff --git a/core/src/mindustry/ui/dialogs/CustomRulesDialog.java b/core/src/mindustry/ui/dialogs/CustomRulesDialog.java
index 634fdac1e8..f45850b0fd 100644
--- a/core/src/mindustry/ui/dialogs/CustomRulesDialog.java
+++ b/core/src/mindustry/ui/dialogs/CustomRulesDialog.java
@@ -35,7 +35,7 @@ public class CustomRulesDialog extends BaseDialog{
 
         banDialog.shown(this::rebuildBanned);
         banDialog.buttons.button("$addall", Icon.add, () -> {
-            rules.bannedBlocks.addAll(content.blocks().select(Block::isBuildable));
+            rules.bannedBlocks.addAll(content.blocks().select(Block::canBeBuilt));
             rebuildBanned();
         }).size(180, 64f);
 
@@ -88,7 +88,7 @@ public class CustomRulesDialog extends BaseDialog{
             dialog.cont.pane(t -> {
                 t.left().margin(14f);
                 int[] i = {0};
-                content.blocks().each(b -> !rules.bannedBlocks.contains(b) && b.isBuildable(), b -> {
+                content.blocks().each(b -> !rules.bannedBlocks.contains(b) && b.canBeBuilt(), b -> {
                     int cols = mobile && Core.graphics.isPortrait() ? 4 : 12;
                     t.button(new TextureRegionDrawable(b.icon(Cicon.medium)), Styles.cleari, () -> {
                         rules.bannedBlocks.add(b);
diff --git a/core/src/mindustry/ui/fragments/PlacementFragment.java b/core/src/mindustry/ui/fragments/PlacementFragment.java
index 3d71dcc635..7f5775b2d7 100644
--- a/core/src/mindustry/ui/fragments/PlacementFragment.java
+++ b/core/src/mindustry/ui/fragments/PlacementFragment.java
@@ -227,7 +227,7 @@ public class PlacementFragment extends Fragment{
                             button.forEach(elem -> elem.setColor(color));
                             button.setChecked(control.input.block == block);
 
-                            if(state.rules.bannedBlocks.contains(block)){
+                            if(!block.isPlaceable()){
                                 button.forEach(elem -> elem.setColor(Color.darkGray));
                             }
                         });
@@ -324,11 +324,11 @@ public class PlacementFragment extends Fragment{
                                 }
                             }).growX().left().margin(3);
 
-                            if(state.rules.bannedBlocks.contains(lastDisplay) || !player.isBuilder()){
+                            if(!lastDisplay.isPlaceable() || !player.isBuilder()){
                                 topTable.row();
                                 topTable.table(b -> {
                                     b.image(Icon.cancel).padRight(2).color(Color.scarlet);
-                                    b.add(!player.isBuilder() ? "$unit.nobuild" : "$banned").width(190f).wrap();
+                                    b.add(!player.isBuilder() ? "$unit.nobuild" : lastDisplay.unplaceableMessage()).width(190f).wrap();
                                     b.left();
                                 }).padTop(2).left();
                             }
@@ -432,7 +432,7 @@ public class PlacementFragment extends Fragment{
         returnArray.sort((b1, b2) -> {
             int locked = -Boolean.compare(unlocked(b1), unlocked(b2));
             if(locked != 0) return locked;
-            return Boolean.compare(state.rules.bannedBlocks.contains(b1), state.rules.bannedBlocks.contains(b2));
+            return Boolean.compare(!b1.isPlaceable(), !b2.isPlaceable());
         });
         return returnArray;
     }
diff --git a/core/src/mindustry/world/Block.java b/core/src/mindustry/world/Block.java
index 7494a2a081..200883de5d 100644
--- a/core/src/mindustry/world/Block.java
+++ b/core/src/mindustry/world/Block.java
@@ -162,6 +162,8 @@ public class Block extends UnlockableContent{
     public float buildCost;
     /** Whether this block is visible and can currently be built. */
     public BuildVisibility buildVisibility = BuildVisibility.hidden;
+    /** Defines when this block can be placed. */
+    public BuildPlaceability buildPlaceability = BuildPlaceability.always;
     /** Multiplier for speed of building this block. */
     public float buildCostMultiplier = 1f;
     /** Whether this block has instant transfer.*/
@@ -298,7 +300,7 @@ public class Block extends UnlockableContent{
     public void setStats(){
         stats.add(BlockStat.size, "@x@", size, size);
         stats.add(BlockStat.health, health, StatUnit.none);
-        if(isBuildable()){
+        if(canBeBuilt()){
             stats.add(BlockStat.buildTime, buildCost / 60, StatUnit.seconds);
             stats.add(BlockStat.buildCost, new ItemListValue(false, requirements));
         }
@@ -465,6 +467,15 @@ public class Block extends UnlockableContent{
         return buildVisibility.visible() && !isHidden();
     }
 
+    public boolean isPlaceable(){
+        return isVisible() && buildPlaceability.placeable() && !state.rules.bannedBlocks.contains(this);
+    }
+
+    /** @return a message detailing why this block can't be placed. */
+    public String unplaceableMessage(){
+        return state.rules.bannedBlocks.contains(this) ? Core.bundle.get("banned") : buildPlaceability.message();
+    }
+
     public boolean isFloor(){
         return this instanceof Floor;
     }
@@ -481,7 +492,7 @@ public class Block extends UnlockableContent{
         return id == 0;
     }
 
-    public boolean isBuildable(){
+    public boolean canBeBuilt(){
         return buildVisibility != BuildVisibility.hidden && buildVisibility != BuildVisibility.debugOnly;
     }
 
diff --git a/core/src/mindustry/world/Build.java b/core/src/mindustry/world/Build.java
index b66273f9fd..c4f925f138 100644
--- a/core/src/mindustry/world/Build.java
+++ b/core/src/mindustry/world/Build.java
@@ -63,11 +63,8 @@ public class Build{
 
     /** Returns whether a tile can be placed at this location by this team. */
     public static boolean validPlace(Team team, int x, int y, Block type, int rotation){
-        if(type == null || !type.isVisible() || type.isHidden()){
-            return false;
-        }
-
-        if(state.rules.bannedBlocks.contains(type) && !(state.rules.waves && team == state.rules.waveTeam)){
+        //the wave team can build whatever they want as long as it's visible - banned blocks are not applicable
+        if(type == null || (!type.isPlaceable() && !(state.rules.waves && team == state.rules.waveTeam && type.isVisible()))){
             return false;
         }
 
diff --git a/core/src/mindustry/world/blocks/campaign/CoreLauncher.java b/core/src/mindustry/world/blocks/campaign/CoreLauncher.java
index 9d3d2c9df0..fd3c0ddd14 100644
--- a/core/src/mindustry/world/blocks/campaign/CoreLauncher.java
+++ b/core/src/mindustry/world/blocks/campaign/CoreLauncher.java
@@ -3,6 +3,7 @@ package mindustry.world.blocks.campaign;
 import mindustry.*;
 import mindustry.gen.*;
 import mindustry.world.*;
+import mindustry.world.meta.*;
 
 import static mindustry.Vars.state;
 
@@ -15,6 +16,7 @@ public class CoreLauncher extends Block{
         hasItems = true;
         configurable = true;
         update = true;
+        buildPlaceability = BuildPlaceability.sectorCaptured;
     }
 
     public class CoreLauncherEntity extends TileEntity{
diff --git a/core/src/mindustry/world/meta/BuildPlaceability.java b/core/src/mindustry/world/meta/BuildPlaceability.java
new file mode 100644
index 0000000000..3799c74207
--- /dev/null
+++ b/core/src/mindustry/world/meta/BuildPlaceability.java
@@ -0,0 +1,32 @@
+package mindustry.world.meta;
+
+import arc.*;
+import arc.func.*;
+import mindustry.*;
+
+import java.util.*;
+
+/**
+ * Like BuildVisiblity, but defines whether a block can be *placed*, with an extra message.
+ * This is like defining a conditionally banned block.
+ * */
+public enum BuildPlaceability{
+    always(() -> true),
+    sectorCaptured(() -> Vars.state.rules.sector != null && Vars.state.rules.sector.isCaptured());
+
+    private final Boolp placeability;
+
+    BuildPlaceability(Boolp placeability){
+        this.placeability = placeability;
+    }
+
+    public boolean placeable(){
+        return placeability.get();
+    }
+
+    /** @return why this block is banned. */
+    public String message(){
+        return Core.bundle.get("unplaceable." + name().toLowerCase(Locale.ROOT));
+    }
+
+}
diff --git a/tests/src/test/java/ApplicationTests.java b/tests/src/test/java/ApplicationTests.java
index 1802564b3f..6cfc6bf7cf 100644
--- a/tests/src/test/java/ApplicationTests.java
+++ b/tests/src/test/java/ApplicationTests.java
@@ -554,7 +554,7 @@ public class ApplicationTests{
 
         for(int x = 5; x < tiles.width && i < content.blocks().size; ){
             Block block = content.block(i++);
-            if(block.isBuildable()){
+            if(block.canBeBuilt()){
                 x += block.size;
                 tiles.get(x, 5).setBlock(block);
                 x += block.size;