Lecture 2.2 Vent & Storm Sewer

cast iron roof drain w/ rubber couplings (no hub)

Vent - The Whole System

vent thru roof (VTR) definition and importance

definition: a Vent Through Roof (VTR) is a vertical plumbing pipe that extends from the drainage and vent (DWV) system up through the roof and opens to the outside air. It allows air to enter and exit the plumbing system.

importance:

• protect trap seals
  By equalizing air pressure in the pipes, a VTR prevents siphoning or back-pressure that could pull water out of P-traps. This keeps sewer gases from entering the building.

• allow proper drainage
  Air admitted through the vent lets wastewater flow smoothly, preventing slow drains, gurgling, and backups.

• release sewer gases safely
  Harmful and foul-smelling gases are vented above the roofline, where they can dissipate safely instead of entering occupied spaces.

• prevent pressure buildup
  The vent relieves positive and negative pressure in the DWV system, reducing stress on pipes and fittings.

waterproofing a VTR?

definition: waterproofing a VTR (Vent Through Roof) is the process of sealing the point where the vent pipe penetrates the roof so rain, snow, and melting ice cannot enter the building.

importance:

• prevents roof leaks that can damage insulation, ceilings, framing, and finishes

• protects structural components from rot, mold, and corrosion

• maintains roof warranty (improper flashing often voids warranties)

air admittance valves (AAV) definition & importance

definition: an Air Admittance Valve (AAV) is a one-way mechanical plumbing vent that opens to allow air into the drainage system when negative pressure occurs and closes to prevent sewer gases from escaping into the building. It is an alternative to running a vent pipe through the roof.

importance:

• protecting P-traps
  They admit air to prevent siphoning of trap seals, keeping sewer gases out of occupied spaces.

• improving drainage performance
  By relieving negative pressure, AAVs reduce slow drains, gurgling, and backups.

• reducing roof penetrations
  Fewer vents through the roof means lower risk of leaks and simpler roof detailing.

• saving space and installation cost
  Useful where routing a vent to the roof is difficult (remodels, island sinks, tight framing).

2-way roof slope

1-way roof slope

internal roof drainage system

primary roof drain definition & importance

definition: primary roof drains are the main drainage outlets designed to remove rainwater from a roof during normal rainfall conditions.

importance:

• carry the full design rainfall load under typical storms

• prevent ponding water that can overstress the roof structure

• protect roofing membranes and insulation

• discharge water into the storm drainage system (interior piping or leaders)

overflow roof drain definition & importance

definition: overflow roof drains are secondary drains or scuppers designed to remove water only when primary drains fail or are overwhelmed.

importance:

• prevent structural collapse from excessive ponding

• provide a visible warning that the primary system is clogged or undersized

• limit water depth on the roof to a safe level

roof drain before insulation

roof drain with insulation

downspout nozzle (cow tongue) importance

• protects foundations by keeping water from pooling at the base of walls

• reduces erosion of soil, landscaping, and paving

• prevents splash-back that can stain walls or damage finishes

• controls discharge direction where no underground storm piping is provided

• improves safety by limiting standing water near walkways

why insulate rood drains?

prevent condensation

• cold rainwater in roof drains can cool the pipe below the indoor dew point

• moist air condenses on the pipe exterior

• insulation prevents water dripping onto ceilings, insulation, and finishes, reducing mold and corrosion

clevis hanger importance (insulated pipes)

• supports pipe weight safely and evenly

• maintains proper pipe slope (critical for sanitary and storm drainage)

• prevents sagging and joint stress

• allows vertical adjustment for precise elevation during installation

swivel ring hanger importance (uninsulated pipes)

• supports pipe weight while allowing slight movement

• accommodates angled or sloped piping, especially in drainage systems

• reduces stress on pipes and fittings

• helps maintain proper pipe alignment and slope

• provides flexibility during installation

scupper in parapet definition & importance

definition: a scupper in a parapet is an opening or outlet built through a parapet wall that allows rainwater to drain off a roof. It directs water from the roof surface through the parapet to the exterior of the building or into a conductor head/downspout.

importance:

• provides roof drainage for flat or low-slope roofs

• acts as overflow protection when primary roof drains are blocked or overwhelmed

• prevents ponding water that can overstress the roof structure

• offers a visible warning of drainage problems when water discharges