In this step, we'll assign the insulation material to the walls and roof. We'll use the material called Glass Wool as an approximation for an insulated wall. A custom material can be created to simulate a stud wall, if desired.
1. Select the wall and roof parts by left clicking on both:
2. Click Edit from the Materials context panel:
3. On the Materials quick edit dialog, select the material type:
4. From the Name menu, select Glass Wool
5. Click Apply.
What it should look like...
6. To verify that the Glass Wool material is properly assigned, check the Design Study Bar and the part coloring: