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ICC P1 practice questions

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Question 1Administration and General Requirements

Under the International Plumbing Code, a plumbing permit becomes null and void if the authorized work is not commenced within how many days after the permit is issued?

  1. 90 days
  2. 365 days
  3. 120 days
  4. 180 days Correct answer.

Explanation

The IPC treats an unstarted permit as expired after 180 days, and the same 180-day limit applies when work is suspended or abandoned after it begins. A new permit would be required before work could lawfully proceed.

Question 2Administration and General Requirements

Who is authorized to approve an alternative plumbing material or method that is not specifically prescribed by the code?

  1. The board of appeals
  2. The project's plumbing engineer
  3. The plumbing contractor
  4. The code official Correct answer.

Explanation

The IPC gives the code official authority to approve an alternative when it is shown to be equivalent to the prescribed material or method. The board of appeals reviews appeals from code official decisions; it does not grant initial approval of alternatives.

Question 3Administration and General Requirements

Before concealing installed plumbing piping that will later be tested, the permit holder must:

  1. Obtain code official approval after inspection Correct answer.
  2. Notify all adjacent property owners in writing
  3. Submit record drawings to the local water utility
  4. Fill the piping with concrete for protection

Explanation

The IPC prohibits covering plumbing work before the code official has inspected and approved it. Approving concealment without that inspection would prevent verification of joints, slope, and support.

Question 4Administration and General Requirements

A code official finds plumbing work being performed contrary to the approved permit and the code. Which action is authorized by the IPC's administrative provisions?

  1. Place a lien on the property
  2. Revoke the contractor's state license
  3. Issue a written stop work order Correct answer.
  4. Order demolition of the entire building

Explanation

The code official may issue a stop work order when work is proceeding contrary to the code or a permit. The order must be in writing, state the conditions to be corrected, and be served on the owner or permit holder.

Question 5Administration and General Requirements

What is the proper role of the board of appeals when a plumbing permit applicant disputes the code official's interpretation of a code requirement?

  1. It may waive any code requirement by a simple majority vote of its members.
  2. It may amend the code text for all future permit applications.
  3. It may interpret the code but not waive requirements. Correct answer.
  4. It may issue the plumbing permit that the code official previously refused.

Explanation

The board of appeals is established to hear challenges to code official decisions involving interpretation or claimed equivalency. The board may grant relief within its authority, but it has no power to set aside a requirement of the adopted code.

Question 6Administration and General Requirements

When the code official determines that an existing plumbing system is unsafe and a hazard to occupants, what action does the IPC authorize?

  1. Suspending all plumbing permits in the jurisdiction
  2. Requiring the installation of a new water meter
  3. Referring the matter exclusively to the state licensing board
  4. Ordering the hazard abated by repair, removal, or disconnection Correct answer.

Explanation

Unsafe plumbing equipment must be repaired, removed, or disconnected so that the hazard is eliminated. The code official gives notice and follows the code's abatement procedures rather than imposing unrelated penalties.

Question 7Administration and General Requirements

Which of the following plumbing activities normally requires a permit under the IPC?

  1. Installing a new floor drain connected to the drainage system Correct answer.
  2. Repairing a leaking fixture supply valve
  3. Clearing a stoppage in a drain line
  4. Removing and reinstalling the same water closet without changing piping

Explanation

The IPC exempts minor repairs such as clearing stoppages, repairing leaks, and removing and reinstalling a water closet when no piping is rearranged. A new floor drain adds a connection to the drainage system and therefore requires a permit.

Question 8Administration and General Requirements

When the code official requires construction documents for a plumbing permit, what must those documents show?

  1. Work location, extent, and character, drawn to scale Correct answer.
  2. The contractor's advertising materials and customer references
  3. A guarantee that no inspections will be required
  4. Only the owner's name and the fixture count

Explanation

Construction documents must be sufficiently complete to show the location, extent, and character of the proposed plumbing work. They are reviewed with the permit application so the code official can determine compliance before issuing the permit.

Question 9Administration and General Requirements

An adopted edition of the IPC references a specific edition of a plumbing materials standard. A newer edition of that standard has since been published. Which edition applies to work permitted under the adopted code?

  1. The newest edition published by the standards organization
  2. The edition referenced in the adopted code Correct answer.
  3. The edition preferred by the material manufacturer
  4. The edition the contractor used on a prior project

Explanation

Referenced standards become enforceable through the specific edition named in the adopted code. A later edition does not apply automatically; it must be adopted by the jurisdiction through the code amendment process.

Question 10Administration and General Requirements

Before approving a plumbing method that is not specifically prescribed by the code, what must the code official determine?

  1. That it is equivalent in strength, effectiveness, durability, and safety Correct answer.
  2. That the method costs less than the method prescribed by the code
  3. That the method has already been used in at least three other jurisdictions
  4. That the contractor carries liability insurance covering the installation

Explanation

The IPC permits approval of alternatives only when the code official finds that they are equivalent to the prescribed method in performance and safety. Cost savings, prior use elsewhere, or insurance alone do not establish equivalency.

Question 11Administration and General Requirements

Under the IPC, who is responsible for keeping the plumbing system of an occupied building in a safe and sanitary condition?

  1. The owner or the owner's authorized agent Correct answer.
  2. The code official, because the system has been inspected
  3. The water purveyor that serves the property
  4. The licensed plumber who installed the system

Explanation

The IPC places responsibility for maintaining plumbing systems on the owner or the owner's authorized agent. Inspections and permits do not shift that duty to the code official, the water utility, or the installing plumber. The installing plumber is responsible for code-compliant installation at the time the work is performed.

Question 12Administration and General Requirements

While plumbing work authorized by a permit is in progress, what must be done with the permit?

  1. It must be kept on the job site and made available to the code official. Correct answer.
  2. It must be filed with the local water utility before work begins.
  3. It must be sent to the board of appeals for its records.
  4. It must be posted at the nearest fire station.

Explanation

The permit or a copy must be kept on the job site until the authorized work is completed so the code official can confirm the scope and validity of the work. Filing the permit with a utility or the board of appeals does not satisfy this requirement, and posting it at a fire station does not make it available for inspection.

Question 13Administration and General Requirements

In the IPC, the term "code official" refers to:

  1. The authority designated to administer and enforce the code Correct answer.
  2. The testing laboratory that lists plumbing materials
  3. The chairperson of the board of appeals
  4. The plumbing contractor who holds the permit and supervises the work

Explanation

The IPC defines the code official as the officer or designated authority charged with administering and enforcing the code, including authorized representatives. Contractors, listing agencies, and board members have separate roles and do not administer the code day to day.

Question 14Administration and General Requirements

A code official arrives at a commercial building to inspect plumbing for which a permit has been issued. The tenant refuses entry. What is the code official's authority under the IPC?

  1. The official must permanently close the permit and take no further action.
  2. Entry is allowed at reasonable times, with legal remedies available if refused. Correct answer.
  3. The official may enter only if the tenant signs a consent form during the visit.
  4. The official may force entry immediately without any legal process.

Explanation

The code official is authorized to enter premises at reasonable times to inspect permitted work. If entry is refused, the code official must use legal remedies such as a warrant rather than forcing entry. Entry does not require a signed consent form obtained during the visit, and refusal does not automatically terminate the permit.

Question 15Administration and General Requirements

Plumbing rough-in work is ready for inspection. Who is responsible for notifying the code official?

  1. The permit holder or the person doing the work Correct answer.
  2. The code official, who must monitor the site daily
  3. The building owner, regardless of who holds the permit
  4. The supplier that delivered the piping materials

Explanation

The permit holder or the person performing the work must notify the code official when the work is ready for inspection. The code official is not required to monitor the site continuously, and owners or suppliers are not the parties responsible for requesting the inspection.

Question 16Administration and General Requirements

The code official discovers that a plumbing permit was issued based on plans that were altered after approval without resubmittal. What is the code official authorized to do?

  1. Take no action until the final inspection
  2. Refer the matter to the water purveyor for immediate disconnection
  3. Double the original permit fee
  4. Revoke the permit Correct answer.

Explanation

The IPC authorizes revocation of a permit where it was issued in error or on the basis of incorrect information, or where the work is contrary to the approved plans or the code. Revocation must be in writing. Doubling fees or directing utility disconnection without legal process is not the authorized response.

Question 17Administration and General Requirements

A code official issues a written notice of violation for an unapproved plumbing installation. What must the notice include?

  1. A description of the violation, the correction required, and a time limit Correct answer.
  2. An order to vacate the building in every case
  3. Only the code section number and the inspector's signature
  4. The penalty amount, set by the inspector without a hearing

Explanation

A notice of violation must be in writing and must describe the violation, state the correction required, and allow a reasonable time for compliance. It is not a penalty assessment made without a hearing, and it does not automatically order the building vacated in every case.

Question 18Administration and General Requirements

A local health ordinance requires a 4-inch building drain where the adopted IPC would permit a 3-inch drain for the same fixture load. A contractor submits plans showing a 3-inch drain. How should the code official proceed?

  1. Approve whichever size costs the owner less
  2. Ask the pipe manufacturer to decide which size applies
  3. Approve the 3-inch drain because the IPC is a model code
  4. Require the 4-inch drain, because the stricter rule governs Correct answer.

Explanation

A valid local ordinance is not nullified by the adopted code, and where requirements differ the more restrictive requirement governs. The code official should require the 4-inch drain. Cost considerations and manufacturer preferences do not resolve conflicts between legal requirements.

Question 19Administration and General Requirements

A homeowner obtains a plumbing permit to replace the water service line in an owner-occupied single-family house. The homeowner performs the work personally. Which statement is correct under the IPC?

  1. The owner may do the work but must follow the code and request inspections. Correct answer.
  2. The owner is exempt from inspections because the work is not being done for hire.
  3. The owner must transfer the permit to a licensed plumber before inspection.
  4. The owner's work is valid only if a licensed plumber signs off afterward.

Explanation

The IPC regulates how plumbing work is installed, not whether the installer is the owner or a contractor. Owner-performed work must still comply with the code and be inspected at the required stages. While some jurisdictions impose licensing limits, the code itself does not exempt owner work from inspections.

Question 20Administration and General Requirements

A new commercial plumbing system has passed its rough-in inspection but not the final inspection. The owner wants to open the building. What does the IPC require?

  1. The system may be used if the contractor signs a written statement of completion.
  2. The system may not be used until the code official approves it. Correct answer.
  3. The system may be used as soon as the water supply is turned on.
  4. The system may be used automatically 30 days after rough-in.

Explanation

Plumbing systems must be inspected and approved before being placed in operation. Passing a rough-in inspection does not authorize use, and neither a contractor's completion statement nor the passage of time substitutes for final approval by the code official.

Question 21Administration and General Requirements

An applicant files a complete plumbing permit application for a commercial tenant improvement. Under the IPC, when must the prescribed permit fee be paid?

  1. Within 30 days after the rough-in inspection is completed
  2. Before the permit is issued Correct answer.
  3. At the time the certificate of occupancy is requested
  4. Only when plan review is performed by a registered design professional

Explanation

The IPC requires the prescribed fees to be paid before a permit is issued; the code official does not issue the permit until the fee is collected. The fee is computed from the work described in the application and the applicable fee schedule, not from later inspection milestones.

Question 22Administration and General Requirements

A plumbing contractor who holds a permit for a building project sells the business, and the buyer intends to finish the remaining plumbing work under the existing permit. Under the IPC, what is the status of that permit?

  1. It is not transferable; the buyer must obtain a new permit Correct answer.
  2. It may be transferred with the written consent of the code official
  3. It remains valid if the buyer keeps the seller's licensed journeymen on the job
  4. It may be transferred once a transfer fee is paid to the jurisdiction

Explanation

The IPC states that permits are not transferable and that a permit holder may not allow another person to do work under the permit. Because the permit runs to the named applicant, a buyer of the business must apply for and obtain a new permit, with a new fee, for the remaining work.

Question 23Administration and General Requirements

During an inspection, a code official learns that a plumbing permit was issued on an application that understated the number of fixtures to be installed, and the fee paid was based on that incorrect information. Under the IPC, which action is the code official authorized to take?

  1. Transfer the permit to the property owner
  2. Suspend the contractor's license until the fee is paid
  3. Revoke the permit Correct answer.
  4. Waive the unpaid fee and allow the work to proceed

Explanation

The code official may revoke a permit where it was issued in error or on the basis of incorrect information supplied, which includes an application that understates fixtures and fees. Revocation is an administrative act under the plumbing code and is separate from any licensing discipline.

Question 24Administration and General Requirements

For a large plumbing project, a code official cannot personally make every inspection but wants independent verification of installed work. Under the IPC, inspection reports may be accepted from which source?

  1. Any licensed plumber employed on the job
  2. The permit holder's project superintendent
  3. An approved inspection agency Correct answer.
  4. The materials supplier's field representative

Explanation

The code official is authorized to accept reports of inspection from approved agencies or individuals where the official does not make all inspections personally. Such reports must be in writing and certified by a responsible officer of the approved agency.

Question 25Administration and General Requirements

A code official inspects and approves a commercial plumbing installation in good faith. Months later a joint fails and causes significant water damage, and the owner sues the official personally, alleging the approval was negligent. Under the IPC, which statement best describes the official's exposure?

  1. The official is personally liable, because an approved inspection certifies the quality of the workmanship
  2. The official is not personally liable when acting in good faith and without malice Correct answer.
  3. The official shares liability with the building owner, who must maintain the system
  4. The official is liable only if the plumbing contractor carries no liability insurance

Explanation

The IPC protects a code official who enforces the code in good faith and without malice from personal liability for damage arising from the performance of those duties. An inspection approval is an administrative determination, not a warranty of workmanship, so responsibility for defective work stays with the parties who installed or own it.

Question 26Fixtures and Fixture Fittings

What is the minimum required liquid seal depth for a plumbing fixture trap under the IPC?

  1. 2 inches Correct answer.
  2. 4 inches
  3. 3 inches
  4. 1 inch

Explanation

The IPC requires each fixture trap to maintain a liquid seal of not less than 2 inches and not more than 4 inches. The minimum seal prevents sewer gas from passing through the trap while still allowing wastewater to flow. A 2-inch seal is the smallest depth that satisfies the code.

Question 27Fixtures and Fixture Fittings

Under the IPC, what is the maximum flush volume for a water closet?

  1. 3.5 gallons per flush
  2. 1.6 gallons per flush Correct answer.
  3. 2.5 gallons per flush
  4. 1.28 gallons per flush

Explanation

The IPC limits water closets to a maximum flush volume of 1.6 gallons per flush. This limit applies to tank-type and flushometer water closets unless a specific code exception applies. Fixtures that use more water per flush do not comply with the standard.

Question 28Fixtures and Fixture Fittings

What is the maximum flow rate for a lavatory faucet under the IPC?

  1. 1.5 gpm at 60 psi
  2. 2.2 gpm at 60 psi Correct answer.
  3. 2.0 gpm at 60 psi
  4. 2.5 gpm at 60 psi

Explanation

The IPC sets the maximum flow rate for lavatory faucets at 2.2 gallons per minute when tested at 60 psi. The limit applies to the fixture fitting and is intended to reduce water use without preventing proper handwashing. Faucets with lower flow rates are permitted.

Question 29Fixtures and Fixture Fittings

What is the minimum size of a water closet compartment in a public restroom?

  1. 30 inches wide by 60 inches deep Correct answer.
  2. 36 inches wide by 60 inches deep
  3. 36 inches wide by 72 inches deep
  4. 30 inches wide by 48 inches deep

Explanation

The IPC requires a water closet compartment to be at least 30 inches wide and 60 inches deep. These dimensions provide the minimum space needed for use of the fixture. Larger compartments are permitted where the room layout allows.

Question 30Fixtures and Fixture Fittings

What is the minimum distance from the centerline of a lavatory to an adjacent sidewall?

  1. 15 inches Correct answer.
  2. 20 inches
  3. 12 inches
  4. 18 inches

Explanation

The IPC requires at least 15 inches from the centerline of a lavatory to a sidewall or partition. This clearance allows a person to stand at the fixture and use it without interference. The distance is measured to the finished wall surface.

Question 31Fixtures and Fixture Fittings

What is the maximum horizontal length of a 1-1/2-inch trap arm from the trap weir to the vent?

  1. 10 feet
  2. 8 feet
  3. 6 feet Correct answer.
  4. 4 feet

Explanation

The IPC limits a 1-1/2-inch trap arm to 6 feet between the trap weir and the vent connection. This distance keeps the trap arm from becoming self-venting or subject to clogging. Larger trap arms are permitted longer distances under the code table.

Question 32Fixtures and Fixture Fittings

What is the minimum interior cross-sectional area of a shower compartment under the IPC?

  1. 1,440 square inches
  2. 1,296 square inches
  3. 900 square inches Correct answer.
  4. 1,024 square inches

Explanation

The IPC requires a shower compartment to have a minimum interior cross-sectional area of 900 square inches. The compartment must also have a minimum dimension of 30 inches. Larger shower compartments are permitted.

Question 33Fixtures and Fixture Fittings

What is the minimum clearance required in front of a water closet?

  1. 24 inches
  2. 18 inches
  3. 21 inches Correct answer.
  4. 15 inches

Explanation

The IPC requires not less than 21 inches of clearance in front of a water closet. This clearance is measured from the front of the fixture to the nearest obstruction. The space is necessary for safe use and access to the fixture.

Question 34Fixtures and Fixture Fittings

A hose bibb installed on the exterior of a building must be protected against backflow by which device?

  1. A check valve
  2. A vacuum breaker Correct answer.
  3. An air gap
  4. A dual check valve

Explanation

The IPC requires hose bibbs to be protected by an atmospheric vacuum breaker or another listed backflow prevention device. A vacuum breaker prevents backsiphonage when a hose is attached and supply pressure drops. A simple check valve does not provide the required protection for this application.

Question 35Fixtures and Fixture Fittings

How must a floor drain trap be protected against evaporation loss?

  1. With a vent
  2. With a cleanout
  3. With a trap primer Correct answer.
  4. With a backwater valve

Explanation

The IPC requires floor drains that are subject to evaporation to have a trap primer or another approved means of maintaining the trap seal. Without a primer, the seal can evaporate and allow sewer gas to enter the building. The primer supplies water to the trap on a regular basis.

Question 36Fixtures and Fixture Fittings

Under the IPC, a drinking fountain is prohibited from being installed in which location?

  1. A toilet room Correct answer.
  2. An office break room
  3. A public park pavilion
  4. A school classroom

Explanation

IPC Section 410.2 prohibits drinking fountains from being installed in a toilet room because of the potential for contamination from splashing and aerosols. Drinking fountains may be installed in classrooms, park pavilions and break rooms when they meet the other requirements of the code.

Question 37Fixtures and Fixture Fittings

What surface characteristics does the IPC require for a water closet seat?

  1. Rough, porous and difficult to clean
  2. Textured, absorbent and slip resistant
  3. Smooth, nonabsorbent and easily cleanable Correct answer.
  4. Cushioned, porous and replaceable

Explanation

Water closet seats must be made of a smooth, nonabsorbent material that can be cleaned easily so that waste and moisture do not penetrate the surface. Absorbent or porous seat materials are not permitted because they can harbor bacteria and odors.

Question 38Fixtures and Fixture Fittings

A floor drain in a public shower room must be provided with which feature so that the trap can be cleaned?

  1. A backwater valve
  2. A removable strainer Correct answer.
  3. A sediment basket with a solid cover
  4. An integral trap primer

Explanation

The IPC requires floor drains to have a removable strainer so debris can be intercepted and the drain and trap can be cleaned. A trap primer and a backwater valve serve different purposes and do not substitute for the strainer.

Question 39Fixtures and Fixture Fittings

Under the IPC, what is the maximum water consumption allowed for a urinal?

  1. 0.5 gallon per flush
  2. 2.5 gallons per flush
  3. 1.0 gallon per flush Correct answer.
  4. 1.6 gallons per flush

Explanation

The IPC limits urinals to a maximum of 1.0 gallon per flush; higher flush volumes are not permitted for new installations. The 1.6-gallon figure applies to water closets, not urinals.

Question 40Fixtures and Fixture Fittings

What is the maximum flow rate allowed for a shower head under the IPC?

  1. 2.5 gallons per minute at 80 psi Correct answer.
  2. 1.5 gallons per minute at 80 psi
  3. 2.0 gallons per minute at 80 psi
  4. 3.0 gallons per minute at 80 psi

Explanation

Shower heads are limited to 2.5 gallons per minute when tested at 80 psi flowing pressure. The rate is a fixture-fitting requirement and applies to the shower head, not to the shower valve or the tub spout.

Question 41Fixtures and Fixture Fittings

What is the minimum diameter required for a bathtub waste outlet and overflow?

  1. 1-1/2 inches Correct answer.
  2. 1-1/4 inches
  3. 3 inches
  4. 2 inches

Explanation

The IPC requires bathtub waste outlets and overflows to be not less than 1-1/2 inches in diameter. This minimum allows the tub to drain adequately while the overflow is functioning.

Question 42Fixtures and Fixture Fittings

A fixture is set directly against a finished wall. How must the joint between the fixture and the wall be finished?

  1. Sealed to make the joint watertight Correct answer.
  2. Left open to permit fixture movement
  3. Covered with a decorative trim plate
  4. Packed with an absorbent filler

Explanation

The IPC requires the joint between a fixture and the wall to be watertight so that water cannot enter the wall cavity or concealed space. Sealant or another approved method is used to close the joint.

Question 43Fixtures and Fixture Fittings

What is the minimum center-to-center spacing between two adjacent urinals under the IPC?

  1. 24 inches
  2. 30 inches Correct answer.
  3. 15 inches
  4. 36 inches

Explanation

Urinals must be spaced not less than 30 inches center to center, and the center of an end urinal must be at least 15 inches from a side wall. The 30-inch dimension provides usable space and privacy between fixtures.

Question 44Fixtures and Fixture Fittings

A sink in a food-handling establishment must be connected to the drainage system in which manner?

  1. Directly to a trapped drain
  2. Directly through a check valve
  3. Through a backwater valve
  4. Through an indirect waste Correct answer.

Explanation

Sinks in food-handling establishments must discharge through an indirect waste so that sewage cannot back up into the sink and contaminate food or utensils. A direct connection, check valve or backwater valve does not provide the required separation.

Question 45Fixtures and Fixture Fittings

A commercial dishwashing machine must discharge its waste through which of the following?

  1. A trap primer
  2. A dual check valve
  3. An air gap or air break Correct answer.
  4. A spring-loaded check valve

Explanation

Commercial dishwashing machine waste must discharge through an air gap or air break, which provides a physical separation between the machine and the drainage system. Check valves and trap primers do not provide the required backflow protection for this fixture.

Question 46Fixtures and Fixture Fittings

A gravity-type water closet flush tank is connected to the potable water supply. Which fitting does the IPC require to protect that supply from backflow?

  1. A flushometer vacuum breaker
  2. A double check valve assembly
  3. A reduced-pressure principle assembly
  4. An antisiphon ballcock Correct answer.

Explanation

The IPC requires gravity flush tanks to be equipped with an antisiphon ballcock. This fitting refills the tank while preventing tank water from being siphoned back into the potable water piping when supply pressure drops.

Question 47Fixtures and Fixture Fittings

What minimum slope must a shower compartment floor have toward the drain under the IPC?

  1. 1/2 inch per foot
  2. 1/4 inch per foot Correct answer.
  3. 1/8 inch per foot
  4. 1 inch per foot

Explanation

The IPC requires shower floors to slope not less than 1/4 unit vertical in 12 units horizontal, which is a 2-percent slope, to the drain. A flatter floor would not reliably drain the shower compartment.

Question 48Fixtures and Fixture Fittings

A shower in a multifamily building is fitted with a single-handle mixing valve. Which valve type does the IPC require to limit temperature changes caused by pressure fluctuations?

  1. A two-handle compression valve
  2. A flushometer valve with a vacuum breaker
  3. A solenoid-operated valve
  4. A pressure-balancing or thermostatic mixing valve Correct answer.

Explanation

The IPC requires shower valves to be of the pressure-balancing or thermostatic mixing type. These designs respond to changes in hot or cold water pressure and limit sudden temperature swings that could scald a bather.

Question 49Fixtures and Fixture Fittings

A clothes washer discharges into a standpipe receptor. What is the required height of the standpipe above the trap weir under the IPC?

  1. Not less than 18 inches and not more than 42 inches Correct answer.
  2. Not less than 12 inches and not more than 24 inches
  3. Not less than 36 inches and not more than 72 inches
  4. Not less than 24 inches and not more than 48 inches

Explanation

The IPC requires a clothes washer standpipe to terminate not less than 18 inches and not more than 42 inches above the trap weir. This range provides an adequate air break and helps prevent the trap from being siphoned by the washer discharge.

Question 50Fixtures and Fixture Fittings

A fixture fitting has a water inlet with a 1-inch effective opening. What is the minimum air gap required by the IPC?

  1. 2 inches Correct answer.
  2. 1 inch
  3. 4 inches
  4. 3 inches

Explanation

The IPC requires an air gap to be at least twice the diameter of the effective opening and never less than 1 inch. For a 1-inch effective opening, twice the opening is 2 inches, so that is the minimum.