previous
  • Tips & Techniques for Painting
    Tips & Techniques for Painting
  • Clever daily tip in your inbox
    Clever daily tip in your inbox
  • Basement Remodeling Tips
    Basement Remodeling Tips
  • Video: Install a Fence
    Video: Install a Fence
  • 7 Trim Carpentry Secrets
    7 Trim Carpentry Secrets
  • 12 Remodeling Secrets
    12 Remodeling Secrets
  • Solid Deck-Framing Advice
    Solid Deck-Framing Advice
  • Master Carpenter Videos
    Master Carpenter Videos
  • Deck Design & Construction
    Deck Design & Construction
  • Gallery: Custom Flooring
    Gallery: Custom Flooring
  • Read FHB on Your iPad
    Read FHB on Your iPad
  • 7 Small Bathroom Layouts
    7 Small Bathroom Layouts
  • All about Roofing
    All about Roofing
  • Energy-Smart Details
    Energy-Smart Details
  • Remodeling in Action
    Remodeling in Action
  • Video Series: Install a Rock-Solid Tile Floor
    Video Series: Install a Rock-Solid Tile Floor
  • 7 Smart Kitchen Solutions
    7 Smart Kitchen Solutions
  • Video: Build a curved step
    Video: Build a curved step
  • Magazine Departments
    Magazine Departments
  • 9 Concrete Countertops Ideas
    9 Concrete Countertops Ideas
next

Sizing a plumbing vent

Q: When I was a plumber’s helper in the 1960s, we used a single 2-1/2-in. galvanized pipe to vent back-to-back kitchens and bathrooms. Nowadays, though, I see 3-in. vent pipe from every bathroom to the outside. Why? Can I hook up my kitchen vent to another 3-in. vent in the attic?





A: Lynn Underwood, a code official in Norfolk, Virginia, replies: Sanitary plumbing systems are complicated to explain, but I’ll try. When we dump water down a drain, it goes to the sewer, which smells bad. Traps use water caught in curved sections of drainpipes to seal the living spaces from sewer gases, the source of those bad smells. To keep the trap water from being sucked down the drain, we add vents.

According to the International Residential Code, every trap or trapped fixture requires a vent. The vent system typically consists of a main vent that extends above the roof far enough to prevent obstruction from snow. Other vents in the house link to this main vent. Vents are required to be at least half the diameter of the drainpipe that they serve, so a 3-in. drainpipe serving a single-family home needs a main vent that is at least 1-1/2 in. dia.

You can connect the kitchen vent to the main vent in the attic as long as the main vent is the proper size and extends through the roof. In earlier codes, a vent pipe was required to be the same size as the building drain, and many plumbers have maintained that tradition, making 3-in. vent pipes still common in houses.



From Fine Homebuilding 165, pp. 108 September 1, 2004