Building over an existing drain or sewer can damage pipes, so that they leak or block, potentially leading to odour nuisance, health problems and environmental damage.
Gall adeiladu dros ddraen neu garthffos ddifrodi pibelli, fel eu bod yn gollwng neu yn llenwi, a gallai hynny arwain at broblemau gydag arogleuon, problemau iechyd a difrod amgylcheddol.