Steep slopes and problem soils in Montgomery County, MD

The details

• Sediment control permit above 5,000 sq ft of disturbance or 100 cubic yards of earth moved.High confidence
• Steep-slope definitions and buffer rules from the 2021 Environmental Guidelines, Chapter III.C.High confidence
• The guidelines are applied in development review (Natural Resources Inventory and forest conservation plans), not to a simple permit on an existing lot.Medium confidence

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Common questions

Do steep slopes or soils like marine clay change what I can build in Montgomery County?

Montgomery has no steep-slope permit for an ordinary house lot. Slopes of 25% or more (15% in Ten Mile Creek and in Special Protection Areas next to wetlands) count as steep in Planning's Environmental Guidelines, which apply when a development plan is reviewed: stream buffers grow to take in the whole slope, and septic fields are banned on slopes over 25%. For a building permit, steep ground mainly shows up through the sediment control permit and engineered foundation and wall designs.

Sources

1. Montgomery County DPS, Permits Required list (land disturbance). Checked 2026-10-21
   Land Disturbance (greater than 5,000 square feet or 100 cubic yards or more of earth movement) [likely requires a permit].
2. Montgomery Planning, Environmental Guidelines (approved 2021), Chapter III.C steep slopes and stream buffers. Checked 2026-10-21
   A slope will be considered steep that... equals or exceeds 15 percent in the portion of the Ten Mile Creek Watershed... equals or exceeds 25 percent in all other areas in the County... [If a stream buffer reaches the toe of a steep slope] the buffer will be…