Drainage Plan
Chapter 8, Section 8-29B of the Montgomery County Code establishes the requirement to control water runoff due to construction of a new single-family dwelling or for additions to single family dwellings located on properties with a lot size of less than 15,000 square feet and where a stormwater management plan has not already been approved. A drainage plan is also required for any new detached Accessory Dwelling Unit regardless of the building square footage or lot size. The applicant must submit a drainage plan that will show the proposed measure to ensure control and/or safe conveyance of any runoff caused by the new construction.
A drainage plan is required prior to issuance of any new residential building permit or an addition to an existing residential building which proposes an increase of more than 400 square feet of the footprint of the building, measured from outside wall to outside wall of the addition, on a residential lot that is less than 15,000 square feet that would drain onto adjacent private property and where a stormwater management plan has not already been approved. A drainage plan is also required for any new detached Accessory Dwelling Unit (ADU) regardless of the building square footage or lot size.
If the residential lot size is 15,000 square feet or greater, regardless of the new roof area, a drainage plan is not required. However, if the scope of work exceeds 5,000 square feet of land disturbance or 100 cubic yards of earth movement, you will need a sediment control permit. A SC permit is ALSO required for construction of a new residential or commercial building regardless of disturbance and for change of use from single family to any other use regardless of disturbance.
There is no additional cost for a drainage plan review and approval. The fee is included in the cost of the associated building permit.
Generally, drainage plan reviews are completed within 1 week. Factors that may impact final approval time include completeness and quality of the submissions and staff workload.