306A Fixture Installation 1 — Questions and Answers
Question 1: What is the standard rough-in measurement for a residential water closet from the finished wall to the centre of the closet flange?
- 10 inches (254 mm)
- 12 inches (305 mm) (Correct answer)
- 14 inches (356 mm)
- 16 inches (406 mm)
Correct answer: 12 inches (305 mm)
The standard rough-in for most residential water closets is 12 inches (305 mm) from the finished wall to the centre of the closet flange. Toilets are manufactured to match this measurement.
Question 2: What type of wax seal is recommended for a water closet installed on a flange that is below the finished floor level?
- Standard wax ring
- Extra-thick wax ring or stacked wax rings (Correct answer)
- Silicone gasket only
- No seal is needed if the flange is tight
Correct answer: Extra-thick wax ring or stacked wax rings
When the closet flange sits below the finished floor surface, an extra-thick wax ring or stacked wax rings are needed to bridge the gap and create a proper seal between the toilet horn and the flange.
Question 3: What is the correct height for a wall-mounted lavatory in a residential bathroom?
- 600 mm (24 inches) from floor to rim
- 750 mm (30 inches) from floor to rim
- 800 mm (31 inches) from floor to rim (Correct answer)
- 900 mm (36 inches) from floor to rim
Correct answer: 800 mm (31 inches) from floor to rim
A wall-mounted lavatory is typically installed at 800 mm (31 inches) from the finished floor to the top of the rim, providing a comfortable height for most adults.
Question 4: What is the minimum centre-to-centre distance between two adjacent water closets?
- 300 mm (12 inches)
- 380 mm (15 inches)
- 600 mm (24 inches)
- 760 mm (30 inches) (Correct answer)
Correct answer: 760 mm (30 inches)
The minimum centre-to-centre distance between two water closets is 760 mm (30 inches) to provide adequate space for comfortable use and maintenance access.
Question 5: When installing a bathtub, what must be done to protect the subflooring?
- Nothing — bathtubs are waterproof
- Install a waterproof membrane or liner under and behind the tub (Correct answer)
- Only seal the drain connection
- Paint the subflooring with primer
Correct answer: Install a waterproof membrane or liner under and behind the tub
A waterproof membrane or liner must be installed under and behind the bathtub to protect the subflooring from water damage caused by splashing, condensation, and potential leaks.
Question 6: What is the purpose of a 'trim kit' when installing a shower valve?
- To seal the valve body to the pipe
- To provide the visible handle, escutcheon plate, and showerhead or spout connection on the finished wall surface (Correct answer)
- To test the valve before use
- To insulate the hot water pipe
Correct answer: To provide the visible handle, escutcheon plate, and showerhead or spout connection on the finished wall surface
The trim kit includes all visible components — the handle, escutcheon (cover plate), and connections for the showerhead or spout — that are installed after the wall is finished, covering the rough-in valve body.
306A Fixture Installation 1
What is the standard rough-in measurement for a residential water closet from the finished wall to the centre of the closet flange?