The Illustrated Rules of Good Bathroom Design
The National Kitchen & Bath Association developed the Bathroom Planning Guidelines to provide designers with good planning practices that consider the typical needs of users. A committee of experts in bathroom design reviewed relevant research, lifestyle, and design trends, and Model Building Code requirements to assure the updated guidelines promote the health, safety, and welfare of consumers.
A bathroom that follows all of these rules is almost guaranteed to be both functional and safe. See how many your existing bathroom violates for a better understanding of why it may seem awkward and dysfunctional.
These formal, printed guidelines are not the only bath design rules. Designers and carpenters have worked out some rules of thumb over many years that do not rise to the level of official national standards but represent a distillation of years of experience and generally accepted industry practice. We have included these in comments where applicable.
The NKBA guidelines are used for academic and educational programs in bathroom design, evaluation of bathroom plans, and testing the competencies of designers seeking certification. For more information and to locate an NKBA member in your area, contact The National Kitchen and Bath Association.
What Do These Fonts Mean?
Guideline: The actual text of an NKBA guideline recommendation.
Code Requirement: Refers to the International Residential Code (IRC) and associated plumbing, electrical, mechanical and access codes. Where appropriate, the requirements of the Americans with Disabilities Act are also indicated. These are taken from Standards for Accessible Design published by the U.S. Department of Justice. Most ADA standards do not apply to private residences. But if you are building or remodeling for a person with limited mobility, they provide a good template for how things should be built. Your local code authority may have modified or added to national requirements, so always check with your local code authority before making any changes to your bathroom
Notes: Are remarks by the publishers of the rule, standard or guideline used to clarify or expand the standard or guideline.
Comments: Are our observations and explanations. If we want to clarify or expand on a guideline, this is where we will do it. We will also use comments to introduce recommendations and rules-of-design that are not a part of the guidelines published by the NKBA.
Guideline 1 – Entry Door
- Clear openings of doorways with swinging doors shall be measured between the face of the door and stop, with the door open 90 degrees. (ANSI 404.2.3) If the door can open a minimum of 93 degrees, the handle may be disregarded in measuring the opening.
- When a passage exceeds 24" in depth, the minimum clear opening increases to 36". (ANSI A117.1 404)
Guideline 2 – Door Interference
Guideline 3 – Ceiling Height
- The general code requirement is that ceilings be at least 90" (7'-6") high but an exception is made for bathrooms which are required to be only 80" (6'-8") high. In any place where a person cannot walk, the ceiling may slope or be dropped down to as low as 60" (5'-0"), and most code officials will allow and even lower drop, especially in bathroom remodels, if it is safe and reasonable under the circumstances.
- The requirement that a shower be at least 30" x 30" x 80" at the shower head is merely practical. Much smaller and the average person would not fit. It is difficult to find a pre-made shower cabinet this small. The usual minimum size is 32" x 32".
- The minimum height of 80" (6'-8") "over the fixture" includes the required minimum clear floor space in front of the fixture, which must also have a minimum height of 80" (6'-8"). See Guideline 4.
- This Guideline must be coordinated with Guideline 9.
- In remodeling bathrooms, this Guideline will have the most impact on bathroom remodels in basements, attics or garrets were ducting or the slope of the roof may reduce the ceiling height over some part of the remodeled bath.
Guideline 4 – Clear Floor Space
- A minimum space of at least 21" must be planned in front of lavatory, toilet, bidet, and tub. (IRC R 307.1)
- A minimum space of at least 24" must be planned in front of a shower entry. (IRC P 2705.1.5)
Guideline 5 – Single Lavatory Placement
- The minimum distance from the centerline of the lavatory to a wall is 15". (IPC 405.3.1)
- The minimum distance between a wall and the edge of a free-standing or wall-hung lavatory is 4". (IRC R 307.2)
Guideline 6 – Double Lavatory Placement
- The minimum distance between the centerlines of two lavatories should be at least 30". (IPC 405.3.1).
- The minimum distance between the edges of two free-standing or wall-hung lavatories is 4". (IRC R 307.1)
Guideline 7 – Lavatory / Vanity Height
Guideline 8 – Countertop Corners
Guideline 9 – Shower Size
Guideline 10 – Tub / Shower Controls
- The shower controls should be accessible from both inside and outside the shower spray and be located between 38"-48" above the floor depending on the user's height.
- The tub controls should be accessible from both inside and outside the tub and be located between the rim of the bathtub and 33" above the floor.
|*Measure to the vertical center of the control. For a wall-mounted showerhead, measure to the vertical center of the shower arm where it meets the wall. For a ceiling-mounted or rain shower, measure to the showerhead when aligned parallel to the floor.|
Guideline 11 – Tub / Shower Control Valves
- Pressure balanced,
- Thermostatic mixing, or
- Combination pressure balance/thermostatic mixing valve types. (IRC P2708.3)
Guideline 12 – Shower Seat
Guideline 13 – Tub / Shower Surround Height
Guideline 14 – Grab Bars
- Plan grab bars to facilitate access to and maneuvering within the tub and shower areas.
- Tub and shower walls should be prepared (reinforced) at time of construction to allow for installation of grab bars to support a static load of 300 lbs.
- Grab bars should be placed at least 33"-36" above the floor.
- Grab bars must be 1-1/4" to 1-1/2" in diameter and extend 1-1/2" from the wall.
Guideline 15 – Windows, Glass, and Glazing
- Glass used in tub or shower enclosures (i.e. tub or shower door) or partitions must be tempered or an approved equal and must be permanently marked as such. (IRC R 308.1)
- If the tub or shower surround has glass windows or walls, the glazing must be tempered glass or approved equal when the bottom edge of glazing is less than 60" above any standing or walking surface. (IRC R 308.4.5)
- Any glazing (i.e. windows or doors) whose bottom edge is less than 18" above the floor must be tempered glass or approved equivalent. (IRC R 308.4.7.2)
Guideline 16 – Tub/Shower Door Swing Direction
Guideline 17 – Bathtub Steps
Guideline 18 – Flooring
Guideline 19 – Equipment Installation and Access
- All equipment, including access panels, must be installed as per manufacturers' specifications. (IRC M 1307.1)
- All manufacturers' instructions must be available for installers and inspectors and left for homeowners. (IRC P 2720.1)
Guideline 20 – Toilet/Bidet Placement
Guideline 21 – Toilet Compartment
Guideline 22 – Storage
Guideline 23 – Bathroom Accessories
- Place a mirror above or near the lavatory at a height that takes the user's eye height into consideration.
- The toilet paper holder should be located 8" to 12" in front of the edge of the toilet bowl, centered at 26" above the floor.
- Additional accessories, such as towel holders, soap dishes, etc., should be conveniently located near all bath fixtures.
Guideline 24 – Electrical Outlets
- At least one GFCI protected receptacle must be installed within 36" of the outside edge of the lavatory. (IRC E 3801.6)
- All receptacles must be protected by Ground-fault-circuit-interrupters (GFCI). (IRC 3802.1)
- A receptacle shall not be installed within a shower or bathtub space. (IRC E 3902.10)
- Switches shall not be installed within wet locations in tub or shower spaces unless installed as part of the listed tub or shower assembly. (IRC E 3901.7)
Guideline 25 – Lighting
- At least one wall-switch-controlled light must be provided. A switch must be placed at the entrance. (IRC E 3901.6, IRC E 3803.2)
- All light fixtures installed within tub and shower spaces should be marked "suitable for damp/wet locations". (IRC E 3903.8)
- Hanging fixtures cannot be located within a zone of 3' feet horizontally and 8' vertically from the top of the bathtub rim. (IRC E 3903.10)
Guideline 26 – Ventilation
The Heating Ventilation Institute (HVI) HVI is an industry association of heating and air conditioning product manufacturers that, among other things, tests and certifies ventilation products and publishes consumer guides on ventilation issues. These are the HVI recommendations for venting bathrooms:
- Small Bathrooms: HVI recommends that in small bathrooms, up to 100 square feet of floor space, the exhaust fan be sized to provide a ventilation rate of 1 cfm per square foot (about eight air changes per hour). This usually results in a ventilation requirement of less than 50 cfm, so the code minimum fan size must be used.
Example 1: The bathroom is 5' x 9' (with 8' ceilings). Multiply 5x9 = bathroom area of 45 sq. ft. At 1 cfm per square foot, the minimum recommendation is a fan rated at 45 cfm. This is less than the code minimum 50 cfm, which must be used.
Medium and Large Bathrooms: For bathrooms larger than 100 square feet in area, HVI recommends a ventilation rate based on the number and type of fixtures present, according to the following table:
Toilet: 50 cfm Shower: 50 cfm Bathtub: 50 cfm Tub/Shower Combo: 50 cfm Whirlpool Tub: 100 cfm Bidet: 50 cfm
To calculate the minimum fan rating, add the cfm for each fixture in the room to arrive at a total cfm.Example 2: The bathroom is 20'x12'. There is a tub, a separate shower enclosure, and a toilet.
Toilet 50 cfm Shower 50 cfm Bathtub 50 cfm Minimum Fan Rating 150 cfm
- Toilet Compartment: If a toilet is in an enclosed stall with a door, then the toilet enclosure is considered by most code authorities to be a separate room. Likewise, if a shower is enclosed right to the ceiling, it will be considered a separate room. These guidelines recommend a separate mechanical exhaust system for "each enclosure", which means a fully enclosed toilet or shower must have its own exhaust fan separate from that of the rest of the bathroom. In most localities, this is also the building code requirement. A steam shower always needs its own ventilation. Strictly follow the manufacturer's recommendation for venting a steam shower. Otherwise, you will have mold growing in places you would not think mold could grow.
Example 3: The bathroom is 15'x15'. There is a tub, a separate, fully enclosed, shower and a fully enclosed toilet in a stall with a door. A fully enclosed toilet or fully enclosed shower should have their own exhaust fans rated at 50 cfm each. The bathroom fan will exhaust only the bathtub and should also be rated at the code minimum 50 cfm.
- How Long to Ventilate: When house air is exhausted to the outside, heat goes with it, meaning that your furnace has to work harder to make up for the lost heat. You want to exhaust moist air to reduce the risk of mold and mildew but once the moist air is gone, you want to stop ventilating. HVI recommends that the fan be left on for a minimum of 20 minutes after use of the bathroom. A timer is a good solution, allowing the fan to turn off automatically at the proper time. There are also fans on the market now that sense the level of humidity in the air and automatically turn on when it is too high, and turn off when it is back to normal. Unfortunately, there is no fan that senses odor, so a manual switch is still necessary.
Guideline 27 – Heating