The Complete Message:
Single foundation area cannot be less than 1m². (TS500 10.3.2)
Solution:
The product of the dimensions of solid and named single footings should provide at least 1m 2 .
Select single footing, single footings.
Enter the properties.
In the General Settings tab, enter enough value to provide 1m2 area in the Dimension X and Dimension Y lines.
