Sorry, you need to enable JavaScript to visit this website.


Menu Button

Plan Review FAQs

Snow Drift & Backflow Valve FAQs

What is snow drift and how does it impact my project's design?
Snow Drift. A snowdrift is a deposit of snow sculpted by wind into a mound during a snowstorm, usually against a parapet, roof top equipment or building wall. Snowdrift may accumulate from wind blowing towards an object “Windward Drift” or blown from a higher source a roof, onto a lower surface “Leeward Drift”.


  • The 2017 DCMR 12A Sections 1608.1 and 2308.1 will reference ASCE 7 Minimum Design Loads and Associated Criteria for Buildings and Other Structures and additional reference guides have taken this condition into account.
  • Section 3307.1 Protection required. Adjoining public and private property shall be protected from damage during construction include roofs. This provision makes neighbor notification and protection of adjoining property a requirement.
  • Once a building is determined to have snow drift exceeding the structural limits; based on the account of the registered design professional performing the work. DCRA requires that some form of mitigation be provided

When does my project require a backflow valve?
Backflow valves installation. A backwater valve is a backflow prevention device used to prevent outbound water through a dwelling's drain pipes from re-entering -- "back flowing"—into a home. The valve contains a flap that allows water to exit the home but closes to prevent the back flow into the home.

  • In Washington, DC, many areas of the city have a combined sewer system. This means that both sanitary water from normal water use (for example, showering, laundry, toilet flushing, etc.) and rainwater or snow melt are carried away in the same sewer system to the Blue Plains Advanced Wastewater Treatment Plant. Your home or building may have the following plumbing connections to the combined sewer system:


Please visit DC Water's website for more information on the DC Water Backwater Valve Rebate Program.

May I have openings (doors or windows) in exterior walls near an adjacent property line or building?
Exterior wall Openings and walls adjacent to lot lines. First Exterior Walls are a wall, bearing or nonbearing, which is used as an enclosing wall for a building. These walls maybe located within 15 feet of a property line, street or an imaginary line between two buildings on the same lot. When this happens windows or openings are restricted.

  • Section 705 of the 2017 DCMR 12A allows for these opening to exist when provided with protection such as fire-resistant glazing, fire shutter or sprinkler coverage.
  • Openings in this area cannot be used for natural light, natural ventilation; smoke control; and emergency evacuation.
  • Theses openings are considered at risk.