Technical Booklet C Site Preparation and Resistance to Contaminants and Moisture·Page 20·4.6
Low-lying buildings and basements - foul water backflow
For protecting low-lying buildings or basements from localised backflow where foul water drainage receives rainwater, guidance is provided in CLG Approved Document H Drainage and waste disposal.
4.6 For protecting low lying buildings or basements from localised backflow where foul water drainage also receives rainwater, information is provided in CLG Approved Document H Drainage and waste disposal. In heavy rainfall these systems surcharge and where preventative measures are not taken this could lead to increased risks of water damage within the property.
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/regional/Technical Booklet C - Site Preparation and Resistance to Contaminants and Moisture.pdf