Steep Slope Information

Construction on Steep Slopes


What is the Steep Slope Ordinance?

Chapter 294 of the Revised Ordinances of the Township of Montclair, known as the Steep Slope Ordinance, was adopted in September 1998 to protect the health, safety and property of Township residents from improper construction on steep slope areas of the Township. The specific purpose of the ordinance is to reduce the hazards peculiar to steep slopes caused by increased surface water runoff, erosion, soil slippage and flooding and insure the proper planning, design and construction to encourage maximum preservation of the natural terrain, avoid excessive clearing of vegetation and provide for environmentally sensitive use of developable land steep slope areas.

When does the ordinance apply?

All lots located in the Steep Slope area indicated on the map are subject to the ordinance, if the average slope of the lot is 10 percent or more and the following work is proposed:

  • New construction exceeding 200 sq. ft. in area;
  • New impervious surfaces (patios, driveways, parking areas, etc.) exceeding 200 sq. ft. in area
  • Grading or removal of vegetation exceeding 1,000 sq. ft. in area.

What do I have to do?

If your project requires building permits, you must first submit your plans to the Construction Office, located on the 2nd floor at 205 Claremont Avenue.

Next, if your property is in the Steep Slope area indicated on the map, you should first confirm that the provisions of the ordinance apply (i.e. check criteria listed under “When does it apply?” above).

If your project meets the site disturbance criteria but you are unsure if it exceeds the 10% average slope, you should arrange to have elevations taken to determine the average slope of your property.

If the average slope is less than 10%, the engineer or surveyor making the determination must submit a letter stating this along with a supporting map showing the elevations and their calculation of the average slope. The letter must be submitted to:

Township Engineer
Montclair Engineering Bureau

219 North Fullerton Avenue
Montclair, NJ 07042

If If building permits are required, a copy of your building permit application must be included. No further steep slope review will be required once the letter has been received.

If the average slope exceeds 10%, you must submit the following information to the Township Engineer:

  1. Boundary survey (property lines), prepared by an NJ licensed Land Surveyor.
  2. Calculated area of site disturbance and new impervious surface (square feet). Plans should also show these areas.
  3. A topographic map (2ft. contours required) showing drainage areas, including drainage onto the site and from the site. Contours must be shown 50 ft. beyond the property line.
  4. Design plan and cross section, sealed by a NJ licensed Engineer (PE), for any structural retaining wall exceeding 4 feet in height.
  5. Computations for existing runoff conditions for a 100-year storm for the time of concentration of the storm drainage area and for a 24-hour duration storm. Drainage calculations and design must be completed by an NJ licensed Engineer (PE). Contact the Engineering Bureau for detailed requirements.
  6. Computations for proposed runoff conditions using the parameters outlined in #2 above.
  7. Computations showing how the site will retain or detain the excess runoff volume for a 100-year, 24-hour duration storm. This volume will be the difference between existing runoff and proposed runoff. Retention/detention methods may include the following: underground

    • stone beds or pits
    • seepage pits
    • retention/detention basins
    • parking lot storage
    • roof storage
    • underground storage chambers

  8. A plan showing existing and proposed drainage conditions, including storm sewers, catch basins/inlets, retention/detention, pipe sizes, etc. Note you must include 50 ft. beyond the property line.

Once this information is received, an engineer may contact you for additional information if needed. Engineering will review the completed application and advise the applicant if permit is approved or denied. If denied, additional site work may be required in order to comply with steep slope requirements.

Link to steep slope GIS map