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Low Salt Design principle: vertical drainage considerations

This section of the manual is currently under construction.

Vertical snowmelt is commonly associated with structures, trees, bridges, awnings, and other elevated surfaces can direct meltwater to sidewalks, steps, and ramps, creating unsafe conditions, accelerating the need for salt and increasing infrastructure damage.

Illustration showing a patch of ice on the sidewalk at the base of a roof drain.age downspout

Meltwater from rooftops, awnings, and other overhead structures that flows across paved surfaces can refreeze, making these areas hazardous to pedestrians.  Image courtesy of Bolton & Menk, Inc. 

Applicability

Some sources of vertical meltwater drainage, like trees, may not be difficult to mitigate.

To minimize repeat salting due to vertical drainage:

  • Design downspouts to direct flow away from saltable surfaces.
  • Use retractable or seasonally removable awnings where possible.
  • If awnings are low enough, remove snow from awnings when snow is removed from adjacent, saltable surface.
  • Standardize awning depth, create a linear sidewalk dripline catch area (planting zone, linear drain, etc.)

Benefits and Limitations

Benefit: Meltwater routed away from saltable surfaces increases public safety since it prevents formation of ice. 

Limitation: It is difficult to collect runoff from some vertical snow catch areas so that it can be routed to a safer area. For example, awnings lining a high traffic sidewalk are installed at a variety of depths and heights. Seldom is there an area to route the meltwater that is not a saltable surface.

Design Criteria and Considerations

Look up!  Look at the entire site/corridor for vertical snow catches. Map out where the snowmelt will drain. Intercept the melt and route it away from saltable surfaces.

For snow catches like decks, avoid placing steps, sidewalks or parking lots under them. If sidewalks must run under decks, capture the meltwater and convey it away from a saltable surface.

Retrofit suitability

High

Permits and regulations

Check local regulations for downspout placement and limitation on how to direct flow from downspouts.

Potential conflicts

It is difficult to control meltwater from awnings.  Awnings are often placed in critical areas such as high use doorways and sidewalks. Awnings add beauty to the building facade but create winter danger and extra salting. Awnings on a stretch of sidewalk vary in height from the building down to the sidewalk, making a system-wide awning catch/retrofit nearly impossible to install.

Research needed

  • Awning meltwater management
  • What share of repeat salting events come from vertical drainage?