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 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.

Code Requirements" refer to International Residential Code (IRC) and associated plumbing, electrical 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 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 you local code authority before making any changes to your bathroom
Notes are remarks by the publishers of the rule, standard or guideline.
Comments" are our observations and explanations.
These formal, printed guidelines are not the only bath design standards. Designers and carpenters have worked out some rules of thumb over many years that do not arise to the level of 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 contact The National Kitchen and Bath Association.

Guideline 1: Entry Door
Recommendation:
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 The clear opening of a doorway should be at least 32". This would require a minimum 34" or 2'-10" door. For universal design, the minimum clear width is 34". If the existing structure precludes changing the opening then a minimum 24" or 2'-0" door is allowable.
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 The door opening width is measured from jamb to jamb. The clear opening width is measured from the inside of the open door to the door stop on the other wise of the opening. It is almost always about 2" narrower than the clear opening.

Building Code Requirement:
The International Residential Code is silent as to door widths and heights of interior doors. Most communities have, however, supplemented the basic code by requiring a minimum 30" door opening in most rooms and 24" for bathrooms and a minimum door height of 80". For bathrooms complying with the Americans with Disabilities Act (ADA), the clear door opening must be 32" wide with the door fully open which usually requires a 34" wide door at minimum.
Notes:
• Clear openings of doorways with swinging doors shall be measured between the face of 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)
Comments:
• Standard door widths include 18", 20", 24", 28", 30", 32" and 36" doors. Any other width and any door wider than 36" is generally made as a custom door.
 
• To achieve a clear opening, the door size must be 2" larger. For example, a 32" clear opening requires a 34" door, and a 36" clear opening requires a 38" door.
 
• Since a 34" (2-10) interior door is typically a special order, custom door, this standard is usually met with a 36" (3-0) standard door. A 36" opening for a narrow passageways requires a 38" door to meet the requirements of ANSI A117.1 404. These are not available except as custom doors — so narrow passageways should be avoided where possible.

Guideline 2: Door Interference
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 Recommendation:
No entry or fixture door should interfere with another door or drawer and/or the safe use of the fixtures or cabinets.

Building Code Requirement:
No International Residential Code requirements.
Comments:
• The entry door should not interfere with a shower door or any cabinet door or drawer.
 
• The entry door should not not interfere with a person using any bathroom fixture or appliance. We commonly find entry and shower doors arranged so they will strike anyone standing in front of the vanity or sink or sitting on the toilet.
 
• In small bathrooms, where space is at a premium, the entry door should, if at all possible, swing out, not in.
 
Guideline 3: Ceiling Height
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 Recommendation:
Same as Building Code Requirement.

Building Code Requirement:
Bathrooms shall have a minimum floor to ceiling height of 80" over the fixture and at the front clearance area for fixtures. A shower or tub equipped with a shower head shall have a minimum floor to ceiling height of 80" above a minimum area 30" X 30" at the shower head. (IRC R305.1.4)
Comments:
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 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".
 
• This Guideline must be coordinated with Guideline 9.
 
Guideline 4: Clear Floor Space
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 Recommendation:
Plan a clear floor space of at least 30" from the front edge of all fixtures (i.e., lavatory, toilet, bidet, tub and shower) to any opposite bath fixture, wall or obstacle.

Building Code Requirement:
• 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
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 Recommendation:
The distance from the centerline of the lavatory to the sidewall/tall obstacle should be at least 20".

Building Code Requirement:
• 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)
Comments:
A pedestal or wall mounted lavatory must meet both of the Building Code Requirements. The center of the lavatory must be at least 15" away from any side wall or tall obstacle, such as a tall cabinet, and the edge of the lavatory must be 4" from the wall or tall obstacle. There are practical reasons for the 4" requirement. Any closer and it would be very difficult to clean the lavatory.
 
Guideline 6: Double Lavatory Placement
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 Recommendation:
The distance between the centerlines of two lavatories should be at least 36".

Building Code Requirement:
• 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
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 Recommendation:
The height of a lavatory or vanity top varies between 32"-43" to fit the user.

Building Code Requirement:
No International Residential Code requirements.
Comments:
This Guideline recognizes that the standard 32" or 36" vanity height is not appropriate for most people. The former practice of installing 32" vanities as a compromise between the best height for children and the best height for adults has fallen by the wayside as builders recognized that after children are grown, adults are stuck with a too-low vanity height for many, many years. The current practice is to install a factory-standard 36" vanity, which is better, but still too low or too high for most people. If young children are using the vanity, rather than lowering the vanity, buy a stool.
 
Guideline 8: Countertop Corners
Recommendation:
Specify clipped or round corners rather than sharp corners on all countertops.

Building Code Requirement:
No International Residential Code requirements.
 
Guideline 9: Shower Size
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 Recommendation:
The interior shower size should be at least 36" x 36".

Building Code Requirement:
The minimum interior shower size is 30" x 30" or 900 square inches, in which a disk of 30" in diameter must fit. (IRC P 2708.1, IPC 417.4)
Comments:
• A shower may be of any shape provided that a disk 30" (36" recommended) in diameter will fit within the walls of the shower and shower head is in the disk area.
 
• Generally to meet the code minimum size, a corner shower with an angled door (neo-angle door shower) cannot be any smaller than 32" x 32". A 30" disk will not fit inside the walls of a 30" x 30" neo angle shower. A minimum neo-angle shower size of 36" x 36" is recommended if space is available.
 
• This Guideline must be coordinated with Guideline 3.
 
Guideline 10: Tub / Shower Controls
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 Recommendation:
• 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 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.

Building Code Requirement:
No International Residential Code requirements.
Comments:
• The guidelines do not specify, but we have always assumed that the height of controls is measured to the vertical center of the control.
 
• The common practice is to install shower and tub controls on the centerline of the tub or shower. This means that to turn on the shower or adjust the water temperature, it is often necessary to reach through the shower water. The better practice is to offset shower controls toward the opening of the shower so that the shower can be adjusted without reaching through the water.
 
• In a tub, the same outboard offset makes it unnecessary to lean into the tub to torn on the water or adjust water temperature, this reduces the risk of slipping or losing balance and falling.
 
• While the Guidelines do not prohibit centerline installation so long as the control can be reached easily from both inside and outside the tub or shower, we know of no situation where that is really possible.
 
• The shower control heights specified by the guidelines are a little rigid. Shower heads should be set at the most comfortable height for the user. If there are multiple users, then a compromise is in order. Here are the heights we use as a guideline. For multiple users, we use the average height of the users. Do not include children in height calculations.

User Height 5' 5'-3"5'-7"6' 6'-3"6'-6"
Shower Controls 38"41" 44" 47"50" 53"
Shower Head 63"68" 71" 75"78" 81"
*Measure to the vertical center of the control. For a shower head, measure to the vertical center of the shower arm where it meets the wall.
 
Guideline 11: Tub / Shower Control Valves

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 The original pressure-balanced shower control invented by Symmons, and still one of the best. Recommendation:
Same as Building Code Requirement.

Building Code Requirement:
Shower and Tub / Shower control valves must be one of the following:
• Pressure balanced,
 
• Thermostatic mixing, or
 
• Combination pressure balance/thermostatic mixing valve types. (IRC P2708.3)
Comments:
These requirements are to reduce the risk of scalding. If the cold water fails for any reason, the shower is prevented from continuing to pump out hot water by these valves that either shut the water off, or rebalance the temperature. It is almost impossible to buy shower control valves that are not either pressure balanced or thermostatic mixing, but some inexpensive valves from generic suppliers do not have these features, so look for one of the other in any shower or tub valve. If a licensed plumber installs the valve, it will almost certainly be one of the other, but it never hurts to ask.
 
Guideline 12: Shower Seat

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 Folding Shower Seat Recommendation:
Plan a seat within the shower that is 17"-19" above the shower floor and 15" deep.

Building Code Requirement:
Shower seat must not infringe on the minimum interior size of the shower (900 square inches). (IRC P 2708.1)
Comments:
• A seat in a shower is not required, but it is a good idea. However, it must not infringe on the minimum interior size of the shower. The shower at the shower head must be large enough for a disk 30" in diameter to fit inside the shower walls. The shower seat must be located out side of this minimum area. See Guideline 9.
 
• One way to reduce the footprint of a shower seat and fit one in a smaller shower is to use a fold up seat. The seat must, however, still be outside the 30" minimum circle when folded down according to most local building codes. Some localities, however, are a little more flexible.
 
• This Guideline must be coordinated with Guidelines 3 and 9.
 
Guideline 13: Tub / Shower Surround Height
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 Recommendation:
The wall area above a tub or shower pan should be covered in a waterproof material extending at least 3" above the showerhead rough in.

Building Code Requirement:
The wall area above a tub or shower pan must be covered in a waterproof material to a height of not less than 72" above the finished floor. (IPC 417.4.1, IRC R 307.2)
 
Guideline 14: Grab Bars
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 Recommendation:
• 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.

Building Code Requirement:
No International Residential Code requirements. The regulations under the Americans with Disabilities Act (ADA) contain requirements for grab bars in ADA compliant housing.
 
Guideline 15: Glazing
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 Recommendation:
Same as Building Code Requirement.

Building Code Requirement:
• 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)
Comments:
• This is a safety measure. Most building and safety codes require tempered glass if glass is installed closer to the floor than 18" because it is easy to break the glass by inadvertently kicking it. This applies to any room in the house, not just the bathroom.
 
• The 60" inch rule is also a safety measure to prevent you from putting your elbow through window glass while showering or bathing. Any glass at or above 60" is considered high enough that it is unlikely to be accidently broken, but any glass lower than 60" is at risk.
 
Guideline 16: Tub/Shower Door Swing Direction
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 Recommendation:
Same as Building Code Requirement.

Building Code Requirement:
Hinged shower doors shall open outward.(IRC P 2708.1)
Comments:
• This is a safety requirement. If an individual loses consciousness or is injured in a shower, his or her body blocking an in-opening tempered glass door would prevent his being reached by emergency medical personnel. As a consequence, even though it may result in water dripping on the floor of the bath, the door must open outward. An alternative, if there is enough space, is a sliding door.
 
• Our local codes officials, however, agree that if a shower has two doors, one of them can be inswinging. The national code is silent on this issue, but it is a logical extension of the code. As long as one door is available for emergency ingress, the swing of the other door is irrelevant to the code.
 
Guideline 17: Bathtub Steps
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 Recommendation:
Steps should not be placed outside a tub. If steps are used a grab bar/hand rail is mandatory.

Building Code Requirement:
No International Residential Code requirements.
Comments:
This guideline refers to permanently installed steps, not temporary, removable steps. Steps in a bathroom where water can make them slippery are not a good idea. There are too many better ways to deal with getting into and out of a bathtub, including the many walk-in bathtub designs on the market.
 
Guideline 18: Flooring
Recommendation:
Slip-resistant surfaces should be specified for the general bath flooring, shower floors, and Tub / Shower bottoms.

Building Code Requirement:
No International Residential Code requirements.
Comments:
• Ceramic tile flooring should have a coefficient of friction (COF) "wet" rating of 0.5 or more. To learn how to choose slip resistant ceramic tile for your bathroom, see Porcelain or Ceramic Tile: What Is the Difference?.
 
• For an overview of the flooring choices available for bathrooms, see "Flooring Options for Kitchens and Baths".
 
Guideline 19: Equipment Installation and Access
Recommendation:
Same as Building Code Requirement.

Building Code Requirement:
• 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)
Comments:
The wording in the building code is confusing. It seems to require that access panels be installed in accordance with the panel manufacturer's instructions. What it really means is that if the manufacturer requires an access to equipment installed in a bathroom, the access panel must be built and must be the size and location specified in the manufacturer's installation instructions. This applies primarily to whirlpool tubs.
 
Guideline 20: Toilet/Bidet Placement
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 Recommendation:
The distance from the centerline of toilet and/or bidet to any bath fixture, wall or other obstacle should be at least 18".

Building Code Requirement:
A minimum distance of 15" is required from the centerline of toilet and/or bidet to any bath fixture, wall or other obstacle. (IRC R 307.2, IRC P 2705.1.5,IPC 405.3.1)
 
Guideline 21: Toilet Compartment
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 Recommendation:
The size for a separate toilet compartment should be at least 36" by 66" with a swing-out or pocket door.
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 If both a bidet and toilet or toilet and wall urinal are built into one compartment, the arrangement of fixtures within the compartment must conform to Guideline 20. This usually results in a compartment between 72" and 75" wide, depending on the width of the fixtures selected.

Building Code Requirement:
The minimum size for a separate toilet compartment is 30" by 60". (IPC 405.3.1)
Comments:
• The Guideline implies that a toilet compartment must have a door. Actually more toilet compartments are built without doors than with.
 
• An inswing door can be used if the width of the door is added to the depth of the compartment. For example, if the compartment has a 24" door, add 24" to the 66" length of the compartment. The new 90" depth accommodates the inswing of the door.
 
• This guideline also applies to a bidet compartment.
 
• If both a bidet and toilet or toilet and wall urinal are built into one compartment, the arrangement of fixtures within the compartment must conform to Guideline 20. This usually results in a minimum compartment width of between 62" and 65", depending on the width of the fixtures selected.
 
• If the compartment needs to be wheelchair accessible, the minimum width is 60".
 
Guideline 22: Storage
Recommendation:
Provide adequate, accessible storage for toiletries, bath linens, grooming and general bathroom supplies at point of use.

Building Code Requirement:
No International Residential Code requirements.
Comments:
Guidelines this vague border on the idiotic. Everyone knows you need "adequate" storage in a bathroom, but what makes storage "adequate"? Since part of what we do in designing bathrooms is to include adequate storage, we have a couple of thoughts on the subject. Towels store in a basket Woven seagrass baskets make excellent storage for rolled towels. About $25.00 each.

Any storage design must comply with the three Iron Rules of Storage:
 
     (1) Items should be stored where they are first used.
 
     (2) Size storage to the things being stored.
 
     (3) Store items in a single layer with no item hidden behind or beneath another.

It may not be possible to conform strictly to the rules in every case, but the closer you can come, the more useful and satisfactory your storage will be. Fortunately, unlike a kitchen where storage can become a very complicated affair, bathroom storage is rather simple because there are many fewer things to store.

Rolled hotel-style towel storage A hotel-style rolled towel rack, about $70.00. In most bathrooms, the things that must be stored are:

• Towels and washcloths: There are no hard and fast rules for the number towels or washcloths needed for each member of the family, but there seems to be a consensus among designers that two of each per person is all that is needed to be stored in the bathroom. Extra towels can be stored elsewhere. Towels are the bulkiest items stored in most baths, but also about the easiest items to store creatively. Colorful towels can add a great deal to the look of the room, so they can be stored on open shelves in plain sight. And, if you decide to change your look, towels are easy and inexpensive to do over.
 
Rolled towels are more compact than folded towels and take up less storage room. And they make a great display. Show off your rolled towels by placing upright inside a wicker basket, canvas bin, metal bucket or something unconventional, such as a small antique trunk. Place the container on the floor or shelf. If you have washcloths that match your towels, roll up each washcloth inside its matching towel.
 
A wine rack can make a great towel holder for rolled towels. Each roll can be set into its own nook, like a wine bottle. As towels are removed and used, the remaining towels won't be disturbed. There are even heavy duty rolled towel holders used mostly by hotels, but also look great in a contemporary bathroom.
 
Make-up drawer with drawer organizer Our handy make-up drawer insert in easy-to-clean acrylic keeps your makeup neat, organized and tidy. We order these from our supplier to exactly fit your drawer. • Toilet paper: At least one spare role of toilet paper should be stored within easy reach of the toilet. Another four or so rolls should be nearby. One idea we like is to store the rolls in a woven basket set next to the toilet. It's convenient and adds an interesting texture to the room. Another good storage space is a narrow cabinet installed on the wall above the toilet. Cleaning supplies in a bucket Storing cleaning supplies in a bucket protects against possible leaks, and tucks neatly under the sink.
 
• First aid kit: According to the American Red Cross, every bathroom should contain a first-aid kit stored inside a handy cabinet. The kit should include assorted adhesive bandages, antibiotic ointment packs, an instant cold compress, hydrocortisone ointment packs, roller bandages, sterile gauze, an oral thermometer and tweezers.
 
• Cleaning supplies: Store all bathroom cleaning supplies, in a plastic bucket inside the vanity. Store the plunger and toilet brush near the cleaning supplies to keep them close at hand but out of sight. A vanity is usually terrible storage. It is dark, full of pipes, and too deep to reach to the back comfortably, or even to see what's in the back. But it works for cleaning supplies in a bucket or other container that can be easily removed.
 
• Toiletries and Make-up: Toiletries and make-up should be stored neatly away and out of sight, not left on the edge of the bathtub or cluttering the sink area. Clutter makes a bathroom look smaller. The best storage solution we have found for makeup is a dedicated makeup drawer. Ours is melamine-coated on the inside to resist damage from spilled makeup and organized using an acrylic insert. If there is no room for a drawer in your vanity, then use a makeup box that can be stored under the sink.
 
Toiletries can be stored in a shallow, in wall cabinet. But the best storage solution we have found is a toiletries box. Fetch the box before a bath then stick everything back in the box and store it away when you are done. If you can't hide the box in a cabinet, use a decorative wicker box instead and set it on a convenient shelf. If bathroom storage is severely limited, you can store the box in your bedroom. The nice thing about toiletry boxes is that each user of the bathroom can have his or her own box — which eliminates arguments about who used the last of the shampoo since everyone has his or her own shampoo. For kids it's a great learning tool. If you forget to tell Mom you're low on shampoo and run out, then, unless you can bribe your brother into sharing, you get to go to school looking like Eddie Munster. It will probably only happen once.
 
• Medicine: Despite the traditional "medicine" cabinets installed in most bathrooms, medicine should never be stored in the bathroom. Heat and steam will damage many medications. Store all over-the-counter pain relievers, anti-allergy medications and prescription medicine in your bedroom, a hallway linen closet, or even the kitchen, but never in the bathroom.
 
Guideline 23: Bathroom Accessories
Recommendation:
Click to Enlarge
 • 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.

Building Code Requirement:
No International Residential Code requirements.
Comments:
• Mirrors: There can be no hard and fast rules for setting a mirror. Mirrors come in various sizes and shapes, and so do users of the bathroom. The general rule we follow is to set the mirror so that the top of the glass portion is a few inches above the eye level of the tallest user. The mirror itself should be tall enough to permit all users to see from the tops of his or her head to the countertop.
 
• Towel Bars and Rings: Towel bars should be set at a convenient height that looks good to you. For most bathrooms, 48" or higher from the finished floor is usually about right. If the bath has a tile wainscot, you may want to adjust this height to avoid drilling through the tile. For children, a lower bar is often more convenient, and encourages hanging up the towel. However, always leave enough space below the towel bar for a towel to hang freely without touching the floor or a surface below the bar. Generally the absolute minimum height is 36" for towels, 18" for wash cloths.
 
• Robe Hooks: Robe hooks should be set at 66" or higher, depending on the height of the user. Tall users might find that a higher hook is needed to keep the robe from touching the floor.
 
Guideline 24: Electrical Outlets
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 Recommendation:
All GFCI receptacles should be located at electrical appliance points of use.

Building Code Requirement:
• 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)
Comments:
• The general rule is that any outlet within 6 feet of a water source must be equipped with a Ground Fault Circuit Interrupter (GFCI). Every outlet in a bath is considered to be within 6 feet of a water source, and so must be a GFCI outlet.
 
• Neither an outlet nor an electrical switch can be located above a bathtub or closer than 36" to any edge of the bathtub. The helps prevent anyone in the tub from touching a switch or outlet and possibly getting electrocuted. Excluded from the prohibition against switches near the tub are the protected switches used to operate the jets in whirlpools, provided the switches are UL listed for near-water use.
 
• Every bathroom must have at least one electrical outlet (in most places it must be at least a duplex outlet) located above or not more than 36" away from the edge of the vanity. If the sink is not located in a vanity, for example a wall-hung sink or pedestal sink, then the outlet may not be more than 36" away from the edge of the sink.
 
Guideline 25: Lighting
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 Recommendation:
In addition to general lighting, task lighting should be provided for each functional area in the bathroom (i.e. grooming, showering).

Building Code Requirement:
• At least one wall-switch controlled light must be provided. 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)
Comments:
• At least one electric light, controlled by a wall switch, must be provided in a bathroom. A pull-chain is no longer allowed. Other sections of the electrical code require that the switch be located near the entry door.
 
• The safest light over a tub or in a shower is a recessed light with a waterproof lens. If a surface-mounted ceiling lamp or hanging (pendant) lamp is used, then it must be 96" above the rim of the rub or 36" outside the edge of the tub. This rule seeks to prevent people losing their balance in the tub from grabbing a handy light cord to steady themselves, and possibly pulling the live light fixture into the water. The light must also be high enough or outside the tub far enough so that a bather could not accidently reach out and touch the light fixture while standing in water.
 
Guideline 26: Ventilation
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 Recommendation:
Plan a mechanical exhaust system, vented to the outside, for each enclosed area.

Building Code Requirement:
Minimum ventilation for the bathroom is to be a window of at least 3 sq. ft. of which 50% is operable, or a mechanical ventilation system of at least 50 cubic feet per minute (cfm) ducted to the outside. (IRC R 303.3, IRC M 1506.3)
Comments:
Using a small window for bathroom ventilation is obsolete, and has been since whole-house heating and cooling virtually eliminated opening windows. Windows never did a particularly good job of ventilating a bathroom anyway. Even if you plan a bathroom window, also plan for adequate mechanical ventilation.

Heating Ventilation Institute (HVI) Recommendations.
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 changers 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:
Toilet50 cfm
Shower50 cfm
Bathtub50 cfm
Tub/Shower Combination50 cfm
Whirlpool Tub100 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
Bathtub50 cfm
Minimum Fan Rating150 cfm
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.

The fully enclosed toilet and 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: Heat
Recommendation:
A supplemental heat source, i.e., heat lamp, toe kick heater, or floor heat, should be considered.

Building Code Requirement:
All bathrooms should have an appropriate heat source to maintain a minimum room temperature of 68° Fahrenheit (20° Celsius).

Comments:
Generally a bathroom should be a tad warmer than the rest of the house when someone is bathing or showering. Normal warm room air on wet skin feels cold. Whatever the supplemental heating solution, it should not involve blowing air. Moving air feels cold no matter how warm it is. Underfloor electric heating, heat lamps, and radiant heating should be considered, but if installed, should include some form of automatic shutoff or timer to ensure the supplemental heat is not left on once the need for it has passed. Otherwise a lot of electricity if wasted.





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