The author of HouseHeating.Components.Walls
probably didn't intended that users of the component should change the table, so therefore it's done in such a away that it isn't visible in the user interface by default. It's a constant
so to see it you can enable the Constants view (View > Constants).
You could also so see it directly if you switch to text view (View > Class Window > Modelica Text View or Ctrl + 3).
![enter image description here](https://community.wolfram.com//c/portal/getImageAttachment?filename=Walls-Constants.png&userId=23166)