diff --git a/app/covid-calculator.ipynb b/app/covid-calculator.ipynb
index c6ede9cf..30531563 100644
--- a/app/covid-calculator.ipynb
+++ b/app/covid-calculator.ipynb
@@ -58,7 +58,7 @@
   },
   {
    "cell_type": "code",
-   "execution_count": 22,
+   "execution_count": 145,
    "metadata": {
     "pycharm": {
      "name": "#%%\n"
@@ -67,40 +67,87 @@
    "outputs": [
     {
      "data": {
+      "text/plain": "VBox(children=(VBox(children=(Label(value='Ventilation type:'), HBox(children=(ToggleButton(value=False, descr…",
       "application/vnd.jupyter.widget-view+json": {
-       "model_id": "a33e789cd87f4cff829c098073adcb4e",
        "version_major": 2,
-       "version_minor": 0
-      },
-      "text/plain": [
-       "VBox(children=(ToggleButton(value=False, description='Mechanical ventilation', layout=Layout(width='100%')), T…"
-      ]
+       "version_minor": 0,
+       "model_id": "ac7739af0c0d456db756d4844a8f1b41"
+      }
      },
      "metadata": {},
      "output_type": "display_data"
     }
    ],
    "source": [
-    "mechanical_button = w.ToggleButton(value=False, description='Mechanical ventilation', layout={'width': '100%'})\n",
-    "acph_text = w.Text(description=\"Air changes per hour\", style={'description_width': 'aut'})\n",
-    "asfr_text = w.Text(description=\"Air supply flow rate\", style={'description_width': '45%'})\n",
+    "ventilation_label = w.Label(\"Ventilation type:\")\n",
+    "mechanical_button = w.ToggleButton(value=False, description='Mechanical', layout={'width': 'auto'})\n",
+    "natural_button = w.ToggleButton(value=False, description='Natural', layout={'width': 'auto'})\n",
     "\n",
-    "def toggle_mechanical(b: w.Button):\n",
-    "    acph_text.disabled = not (mechanical_button.value or asfr_text.value)\n",
-    "    asfr_text.disabled = not (mechanical_button.value or acph_text.value)\n",
+    "acph_text = w.Text(description=\"Air changes per hour\", style={'description_width': 'auto'})\n",
+    "asfr_text = w.Text(description=\"Air supply flow rate\", style={'description_width': 'auto'})\n",
     "\n",
     "w.jsdlink((acph_text, 'value'), (asfr_text, 'disabled'))\n",
     "w.jsdlink((asfr_text, 'value'), (acph_text, 'disabled'))\n",
-    "acph_text.disabled = True\n",
-    "asfr_text.disabled = True\n",
-    "\n",
-    "mechanical_button.observe(toggle_mechanical)\n",
     "\n",
     "mech_vent_box = w.VBox(\n",
-    "    children=(mechanical_button, acph_text, w.Label(value=\"------- OR -------\"), asfr_text),\n",
-    "    layout=w.Layout(align_items='center')\n",
-    ")"
+    "    children=(acph_text, w.Label(value=\"------- OR -------\"), asfr_text),\n",
+    "    layout=w.Layout(display='none')\n",
+    ")\n",
+    "\n",
+    "nat_vent_box = w.VBox(\n",
+    "    children=(\n",
+    "        w.Text(description='Number of windows:', style={'description_width': 'auto'}),\n",
+    "        w.Text(description='Height of window:', placeholder='meters', style={'description_width': 'auto'}),\n",
+    "        w.Text(description='Width of window:', placeholder='meters', style={'description_width': 'auto'}),\n",
+    "        w.Text(description='Opening distance:', placeholder='centimeters', style={'description_width': 'auto'}),\n",
+    "        w.HBox(children=(\n",
+    "            w.Label('Windows open'),\n",
+    "            w.RadioButtons(options=('Always', '15 min / 2h'))\n",
+    "        ))\n",
+    "    ),\n",
+    "    layout=w.Layout(align_items='center', display='none'),\n",
+    ")\n",
+    "\n",
+    "\n",
+    "\n",
+    "tab_bar = w.HBox(children=(mechanical_button, natural_button))\n",
+    "ventilation_type_menu = w.VBox(children=(ventilation_label, tab_bar), layout=w.Layout(align_items='center', width='auto'))\n",
+    "ventilation_menu = w.VBox(children=(ventilation_type_menu, mech_vent_box, nat_vent_box),\n",
+    "                          layout=w.Layout(align_items='center'))\n",
+    "\n",
+    "def handle_natural_toggle(_):\n",
+    "    if natural_button.value:\n",
+    "        mechanical_button.value = False\n",
+    "        ventilation_menu.children[2].layout.display = 'block'\n",
+    "    else:\n",
+    "        ventilation_menu.children[2].layout.display = 'none'\n",
+    "\n",
+    "def handle_mechanical_toggle(_):\n",
+    "    if mechanical_button.value:\n",
+    "        natural_button.value = False\n",
+    "        ventilation_menu.children[1].layout.display = 'block'\n",
+    "    else:\n",
+    "        ventilation_menu.children[1].layout.display = 'none'\n",
+    "\n",
+    "natural_button.observe(handle_natural_toggle)\n",
+    "mechanical_button.observe(handle_mechanical_toggle)\n",
+    "\n",
+    "ventilation_menu"
    ]
+  },
+  {
+   "cell_type": "code",
+   "execution_count": null,
+   "outputs": [],
+   "source": [
+    "natural_button = w.ToggleButton(value=False, description='Mechanical ventilation', layout={'width': '100%'})\n"
+   ],
+   "metadata": {
+    "collapsed": false,
+    "pycharm": {
+     "name": "#%%\n"
+    }
+   }
   }
  ],
  "metadata": {