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Plumber Red Seal · Question

In a high-rise building, what is the purpose of an offset relief vent in a soil or waste stack?

When falling waste hits a horizontal offset in a tall stack, the air below is compressed. A relief vent connects the stack below the offset back to the main ven

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Question: In a high-rise building, what is the purpose of an offset relief vent in a soil or waste stack?

Answer options:

  • To provide an additional source of air for the lower floors ✅ To relieve positive pressure created at the base of the offset
  • To allow for thermal expansion of the vertical stack
  • To serve as a cleanout for the horizontal offset section

Correct answer: To relieve positive pressure created at the base of the offset

Explanation: When falling waste hits a horizontal offset in a tall stack, the air below is compressed. A relief vent connects the stack below the offset back to the main vent stack, safely dissipating this positive pressure and preventing it from blowing out trap seals on lower floors.

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