Related Rule
South Africa
Practice Relating to Rule 10. Civilian Objects’ Loss of Protection from Attack
Section A. Civilian objects used for military purposes
South Africa’s LOAC Teaching Manual (2008) states:
Objects, which are normally civilian objects, can, according to the military situation, become military objectives (E.g. a house or a bridge being used for tactical defence purposes).
Civilians can lose their protection under the LOAC [law of armed conflict] for such times as they take a direct part in hostilities. Civilian objects used for hostilities similarly lose their protection. 
South Africa, Advanced Law of Armed Conflict Teaching Manual, School of Military Justice, 1 April 2008, as amended to 25 October 2013, Learning Unit 2, pp. 54 and 125.