Technical Regulations (TEK) Section 8.37:
"The pitch of a roof should be such that rain and melted snow can drain off."
Guidelines regarding Technical Regulations (REN) Section 8.37:
"A roof should be designed so that rain and melted snow does not infiltrate the roof construction. The pitch should be steep enough to prevent water from forming puddles on the roofing. Water must be channelled away from the building construction by using guttering and down-pipes.”
Our interpretation of the above is that large quantities of water should not accumulate on the roof, but should be drained off. However, if a few small puddles containing 2-3 cm of water are left behind on a flat roof, such cannot be considered to conflict with TEK and REN. Customary practice relating to what it is possible to achieve within current tolerances for materials and constructions indicates that this is satisfactory.
The puddles may be larger on ballasted, flat roofs, covered with a layer of either gravel or turf. If it has been raining for a long time puddles containing 6-8 cm of water may form. Customary practice indicates that even in such cases this is acceptable, and therefore cannot be said to conflict with TEK and REN.