diff --git a/diylc/diylc-core/src/main/java/org/diylc/core/IBoardSideComponent.java b/diylc/diylc-core/src/main/java/org/diylc/core/IBoardSideComponent.java
new file mode 100644
index 000000000..305a0a5ee
--- /dev/null
+++ b/diylc/diylc-core/src/main/java/org/diylc/core/IBoardSideComponent.java
@@ -0,0 +1,42 @@
+/*
+
+    DIY Layout Creator (DIYLC).
+    Copyright (c) 2009-2025 held jointly by the individual authors.
+
+    This file is part of DIYLC.
+
+    DIYLC is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    DIYLC is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with DIYLC.  If not, see <http://www.gnu.org/licenses/>.
+
+*/
+package org.diylc.core;
+
+import org.diylc.common.PCBLayer;
+
+/**
+ * Interface for components mounted on one side of a board, such as a resistor or an IC. The side
+ * says where the part sits physically; it is separate from {@link ILayeredComponent}, which drives
+ * continuity, because the leads of a through-hole part connect to copper on both sides whichever
+ * side the part is mounted on. Components whose copper already has a layer (traces, pads, ground
+ * fills) do not implement it.
+ * 
+ * @author Branislav Stojkovic
+ */
+public interface IBoardSideComponent {
+
+  /**
+   * @return {@link PCBLayer#_2} for the top of the board or {@link PCBLayer#_1} for the bottom,
+   *         never an inner layer or null
+   */
+  PCBLayer getBoardSide();
+}
diff --git a/diylc/diylc-core/src/main/java/org/diylc/core/gerber/GerberExporter.java b/diylc/diylc-core/src/main/java/org/diylc/core/gerber/GerberExporter.java
index a19ddffa0..decba7804 100644
--- a/diylc/diylc-core/src/main/java/org/diylc/core/gerber/GerberExporter.java
+++ b/diylc/diylc-core/src/main/java/org/diylc/core/gerber/GerberExporter.java
@@ -16,8 +16,10 @@ import org.apache.log4j.Logger;
 
 import com.bancika.gerberwriter.DataLayer;
 
+import org.diylc.common.PCBLayer;
 import org.diylc.core.ComponentState;
 import org.diylc.core.IBoard;
+import org.diylc.core.IBoardSideComponent;
 import org.diylc.core.IDIYComponent;
 import org.diylc.core.IView;
 import org.diylc.core.Project;
@@ -158,8 +160,14 @@ public class GerberExporter {
       gerberComponentCustom.draw(g2d, ComponentState.NORMAL, outlineMode, currentProject, g2d, g2d);
     } else if (gerberComponent instanceof IGerberComponentSimple) {
       IGerberComponentSimple gerberComponentSimple = (IGerberComponentSimple) gerberComponent;
-      g2d.startGerberOutput(gerberComponentSimple.getGerberLayer(),
-              gerberComponentSimple.getGerberFunction(), gerberComponentSimple.isGerberNegative());
+      GerberLayer layer = gerberComponentSimple.getGerberLayer();
+      // components emit their top-side layer; a part mounted underneath goes to the bottom one
+      if (c instanceof IBoardSideComponent
+          && ((IBoardSideComponent) c).getBoardSide() == PCBLayer._1) {
+        layer = layer.flip();
+      }
+      g2d.startGerberOutput(layer, gerberComponentSimple.getGerberFunction(),
+              gerberComponentSimple.isGerberNegative());
       c.draw(g2d, ComponentState.NORMAL, outlineMode, currentProject, g2d);
       g2d.stopGerberOutput();
     }
diff --git a/diylc/diylc-core/src/test/java/org/diylc/core/gerber/GerberExporterTest.java b/diylc/diylc-core/src/test/java/org/diylc/core/gerber/GerberExporterTest.java
index e76abe62f..71afb77d6 100644
--- a/diylc/diylc-core/src/test/java/org/diylc/core/gerber/GerberExporterTest.java
+++ b/diylc/diylc-core/src/test/java/org/diylc/core/gerber/GerberExporterTest.java
@@ -29,7 +29,9 @@ import java.awt.geom.Rectangle2D;
 import java.awt.image.BufferedImage;
 import java.util.EnumSet;
 
+import org.diylc.common.PCBLayer;
 import org.diylc.core.ComponentState;
+import org.diylc.core.IBoardSideComponent;
 import org.diylc.core.IDrawingObserver;
 import org.diylc.core.Project;
 import org.diylc.testcomponents.MockDIYComponent;
@@ -51,6 +53,27 @@ public class GerberExporterTest {
     assertEquals(EnumSet.of(GerberLayer.CopperBot), EnumSet.copyOf(g2d.getLayerMap().keySet()));
   }
 
+  @Test
+  public void testTopSideComponentKeepsItsLayer() {
+    GerberG2DWrapper g2d = draw(new SidedGerberComponent(PCBLayer._2));
+
+    assertEquals(EnumSet.of(GerberLayer.SilkscreenTop), EnumSet.copyOf(g2d.getLayerMap().keySet()));
+  }
+
+  @Test
+  public void testBottomSideComponentGoesToTheOtherSide() {
+    GerberG2DWrapper g2d = draw(new SidedGerberComponent(PCBLayer._1));
+
+    assertEquals(EnumSet.of(GerberLayer.SilkscreenBot), EnumSet.copyOf(g2d.getLayerMap().keySet()));
+  }
+
+  @Test
+  public void testComponentWithoutSideStaysOnTop() {
+    GerberG2DWrapper g2d = draw(new SidedGerberComponent(null));
+
+    assertEquals(EnumSet.of(GerberLayer.SilkscreenTop), EnumSet.copyOf(g2d.getLayerMap().keySet()));
+  }
+
   private static GerberG2DWrapper draw(SimpleGerberComponent component) {
     BufferedImage img = new BufferedImage(100, 100, BufferedImage.TYPE_INT_ARGB);
     Graphics2D graphics = img.createGraphics();
@@ -85,4 +108,22 @@ public class GerberExporterTest {
       g2d.fill(new Rectangle2D.Double(10, 10, 20, 20));
     }
   }
+
+  public static class SidedGerberComponent extends SimpleGerberComponent
+      implements IBoardSideComponent {
+
+    private static final long serialVersionUID = 1L;
+
+    private PCBLayer side;
+
+    public SidedGerberComponent(PCBLayer side) {
+      super(null);
+      this.side = side;
+    }
+
+    @Override
+    public PCBLayer getBoardSide() {
+      return side;
+    }
+  }
 }
diff --git a/diylc/docs/plans/bottom-side-components.md b/diylc/docs/plans/bottom-side-components.md
index 907a6c7db..0b51e5fec 100644
--- a/diylc/docs/plans/bottom-side-components.md
+++ b/diylc/docs/plans/bottom-side-components.md
@@ -3,8 +3,9 @@
 Let a component be mounted on the bottom of a PCB, so that its silkscreen goes to the bottom
 Gerber layers and the canvas shows it as a part on the far side of the board.
 
-Status: the Gerber dispatch is a single method and `GerberLayer.flip()` exists, with tests; the
-next steps below remain.
+Status: the core Gerber side is done, with tests: `IBoardSideComponent` exists and the export
+sends a bottom-side part to the bottom layers. No component implements it yet; the next steps below
+remain.
 
 ## 1. Current state
 
@@ -20,10 +21,12 @@ next steps below remain.
   default (resistors, film and radial capacitors, diodes, LEDs, transistor packages, DIL/SIL ICs,
   SMD passives, switches, jacks, relays, transformers, tube sockets, ...). None of them emit copper.
   Their pads are separate `SolderPad` components, which already have a layer.
-- One method decides the layer for a simple component: `GerberExporter.drawComponent`, which
-  calls `g2d.startGerberOutput(getGerberLayer(), ...)`. It is package-private so that
-  `GerberExporterTest` can call it. `GerberLayer.flip()` maps a layer to the other side of the
-  board.
+- One method decides the layer for a simple component: `GerberExporter.drawComponent`. It is
+  package-private so that `GerberExporterTest` can call it. It uses `getGerberLayer()`, flipped
+  with `GerberLayer.flip()` when the component is an `IBoardSideComponent` on `_1` (Bottom).
+- **`org.diylc.core.IBoardSideComponent`**: `PCBLayer getBoardSide()`, returning `_1` or `_2`
+  only. It is deliberately separate from `ILayeredComponent` (see Decisions). Core knows a part's
+  side only through this interface.
 - Z-order is paint order only. A trace on the bottom layer already paints above the board
   (`zOrder = TRACE`), so the codebase already treats the physical side as separate from z-order.
 
@@ -43,11 +46,6 @@ next steps below remain.
 
 ### diylc-core
 
-- **`org.diylc.core.IBoardSideComponent`**: `PCBLayer getBoardSide();` with Javadoc and
-  `@author`, in the same shape as `ILayeredComponent` but deliberately separate from it (see
-  Decisions). It returns `_1` or `_2` only. Core knows the side only through this interface.
-- **Gerber dispatch**: in the simple-component branch of `GerberExporter.drawComponent`, use
-  `getGerberLayer().flip()` when the component is an `IBoardSideComponent` on `_1`.
 - **Canvas rendering**: bottom-side components use the far-side fade from `copper-side-view.md`,
   wrapping their painting in `startDrawingSide(getBoardSide())`. They are then faded in the main
   view and solid in the Underside Display mirror, the same as bottom copper.
@@ -133,8 +131,8 @@ order.
 
 ## 5. Verification
 
-- `GerberLayerTest` covers `flip()`. `GerberExporterTest` covers the dispatch for simple components;
-  extend it with a stub `IBoardSideComponent` (top, bottom and `null`).
+- `GerberLayerTest` covers `flip()`. `GerberExporterTest` covers the dispatch for simple components,
+  including a stub `IBoardSideComponent` on top, bottom and `null`.
 - Load an old `.diy` with PCB parts and confirm every component reports `_2` (Top) and that the Gerber
   output is byte-identical to before.
 - Export a board with one part on each side and open the files in a Gerber viewer: the bottom part
@@ -148,15 +146,14 @@ order.
 
 ## 6. Next steps
 
-1. Add `IBoardSideComponent` and swap the Gerber layer in the dispatch.
-2. Add the field to the library components, putting it on shared bases where they exist. Settle
+1. Add the field to the library components, putting it on shared bases where they exist. Settle
    the silkscreen-text question while doing so.
-3. Wrap bottom-side painting in `startDrawingSide(getBoardSide())`.
-4. Add the Flip to Other Side action.
-5. Split the silkscreen print-out by side.
-6. Extract the mirror geometry helper, with tests, and use it in `drawMirroredComponent`.
-7. Mirror stage 1: selecting through the mirror. It does not depend on steps 1-5 and can ship
+2. Wrap bottom-side painting in `startDrawingSide(getBoardSide())`.
+3. Add the Flip to Other Side action.
+4. Split the silkscreen print-out by side.
+5. Extract the mirror geometry helper, with tests, and use it in `drawMirroredComponent`.
+6. Mirror stage 1: selecting through the mirror. It does not depend on steps 1-4 and can ship
    early.
-8. Mirror stage 2: dragging through the mirror.
-9. Mirror stage 3: placing in the mirror, after Flip to Other Side exists.
-10. Run the regression suite.
+7. Mirror stage 2: dragging through the mirror.
+8. Mirror stage 3: placing in the mirror, after Flip to Other Side exists.
+9. Run the regression suite.