One of the most important concepts in TFP is related with the exterior walls: the exterior walls in TFP must conform an enclosed perimeter, otherwise some features won't work (topography will be inside the house, automatic roof is not available, dimensions will not follow the rules for exterior walls, etc). For this reason, it is always important that you check if the exterior walls are really fused.
So my first suggestion is that you check if all the walls in the perimeter are 100% fused => in this way, you will be able to set the correct elements, including walls with different thickness.
Now, regarding the walls with different thickness => keep in mind these two concepts :
- if you have two walls and you join them using the arrows of your keyboard, you are just connecting the walls => this means that the walls are together but they are independent--> they don't share the properties or thickness and they work as 2 separated walls.
- if you have two walls and you join them using the mouse, you are merging the walls--> this means that the walls are fused --> they share the properties (and thickness) and they work as only one wall.
Hope this helps,