So if there is an existing drain below, or close to, your proposed extension, it may need to be moved or protected, which is likely to increase the cost of your project.
Felly os oes draen dan y ddaear, neu yn agos at eich estyniad arfaethedig, mae'n bosibl y bydd angen ei symud neu ei warchod, sy'n debygol o godi costau eich prosiect.