306A Fixture Installation 4 — Questions and Answers
Question 1: What is the proper method for levelling a bathtub during installation?
- Use wooden shims under the tub feet and set in a mortar bed (Correct answer)
- Rely on the floor being perfectly level
- Tilt the tub slightly toward the drain end
- No levelling is needed for modern tubs
Correct answer: Use wooden shims under the tub feet and set in a mortar bed
Bathtubs should be levelled using shims or set in a mortar bed to ensure proper drainage and prevent flexing. Some manufacturers recommend a slight pitch toward the drain, but the rim should be level for proper water containment.
Question 2: What is the minimum trap size for a residential shower drain?
- 1¼ inch
- 1½ inch
- 2 inch (Correct answer)
- 3 inch
Correct answer: 2 inch
Residential showers require a minimum 2-inch trap because of the relatively high flow rate from showerheads and the continuous nature of shower drainage during use.
Question 3: When installing a wall-hung water closet, what must be installed within the wall?
- Standard 2x6 framing only
- A concealed carrier frame engineered to support the weight of the toilet and user (Correct answer)
- Additional drywall reinforcement
- A plywood backer board
Correct answer: A concealed carrier frame engineered to support the weight of the toilet and user
A wall-hung water closet requires a concealed steel carrier frame that transfers the weight load to the floor structure. These carriers are engineered to support the toilet plus the user's weight (typically rated for 200 kg or more).
Question 4: What is the purpose of insulating hot water supply pipes under a kitchen or bathroom sink?
- To prevent pipe sweating
- To protect users from burns if they contact the hot pipe, particularly in accessible installations (Correct answer)
- To reduce noise from water flow
- To prevent the pipe from corroding
Correct answer: To protect users from burns if they contact the hot pipe, particularly in accessible installations
Insulating exposed hot water pipes under sinks protects users from burn injuries if they accidentally touch the pipe. This is particularly important in accessible installations where wheelchair users may have legs positioned near the pipes.
Question 5: What is the standard rough-in height for a tub spout?
- 100 mm (4 inches) above the tub rim (Correct answer)
- 150 mm (6 inches) above the tub rim
- 300 mm (12 inches) above the tub rim
- Flush with the tub rim
Correct answer: 100 mm (4 inches) above the tub rim
The standard rough-in height for a tub spout is approximately 100 mm (4 inches) above the tub rim, providing clearance for the spout to discharge into the tub without excessive splashing.
Question 6: When installing a dishwasher, why must the drain hose be looped up to the underside of the counter before connecting to the sink drain or disposer?
- To reduce vibration
- To create a high loop that prevents waste water from the sink from draining back into the dishwasher (Correct answer)
- To make the hose easier to service
- To slow the discharge flow rate
Correct answer: To create a high loop that prevents waste water from the sink from draining back into the dishwasher
The high loop acts as a simple backflow prevention method, preventing sink waste water from flowing back into the dishwasher by gravity. In some jurisdictions, an air gap device is required instead of or in addition to the high loop.
306A Fixture Installation 4
What is the proper method for levelling a bathtub during installation?