INTERIOR ENVIRONMENT

Section 1203 Ventilation

Section 1204 Temperature Control

Section 1205 Lighting

Section 1206 Yards or Courts

Section 1207 Sound Transmission

Section 1208 Interior Space Dimensions

Section 1209 Access to Unoccupied Spaces

Section 1210 Toilet and Bathroom Requirements

Key Points

Section 1203 Ventilation

Ventilation in buildings is regulated based on the ventilating method used. This section addresses the use of natural ventilation, whereas the use of mechanical ventilation is regulated by the International Mechanical Code® (IMC®).

1203.2   Ventilation required.   During cold weather, condensation is deposited on cold surfaces when, for example, warm, moist air rising from the interior of the building and through the attic comes in contact with the roof deck. This alternative wetting and drying that is due to condensation creates dry rot in the wood, and preventive measures are required. In attic areas of noncombustible construction, it is also important to ventilate the area, particularly in light-gauge steel construction. Therefore, enclosed attics and enclosed rafter spaces formed where ceilings are applied directly to the underside of roof-framing members, such as in cathedral ceiling applications, are to have cross ventilation for each separate space. Ventilation of the attic prevents moisture condensation on the cold surfaces and, therefore, will prevent dry rot on the bottom surfaces of shingles or wood roof decks. Figure 1203-1 provides three examples of attic ventilation. In the areas where the moisture condensation is a particular problem or where the normal requirement for attic ventilation cannot be provided, ventilation of the attic by mechanical exhaust fans may be required. Exhaust fans are particularly beneficial in all cases because of the extra movement of the air provided.

Figure 1203-1   Attic ventilation.

The method and arrangement of providing ventilated openings is an important aspect in the proper ventilation of attic spaces. It is critical that any such openings be protected against the entrance of rain and snow. In addition, blocking and bridging that is installed must be located so as to not interfere with the movement of air. At least 1 inch (25 mm) of air space must be provided between the insulation and the roof sheathing, as shown in Figure 1203-2. The net free ventilating area must be at least 1/150 of the area of the space ventilated. Two exceptions permit a reduction in the amount of ventilating area to 1/300 of the attic area being ventilated, provided specific criteria are met. Exception 2 is illustrated in Figure 1203-3.

Figure 1203-2   Attic ventilation—air space.

Figure 1203-3   Attic ventilation—calculations.

Something often overlooked when sizing attic vents is that the code requires that the area provided be the net free area. The net free area can be as much as 50 percent less than the gross area. For example, one manufacturer’s 24-inch (610-mm) square gable vent [gross area equals 576 square inches (0.37 m²)] is listed in their catalog as having a net free area of 308 square inches (0.20 m²), which is about 53 percent of the gross area. The manufacturer’s literature for the specific vents being used needs to be consulted in order to obtain accurate free area information.

1203.2.1   Openings into attic.   Exterior ventilation openings are required by the code to be screened in order to prevent entry of birds, squirrels, rodents, and other similar creatures. A mesh size between inch (1.6 mm) and ¼ inch (6.4 mm) is required to address the problems of both smaller openings being blocked by debris and spider webs, and larger openings permitting access to small rodents. In addition to the use of corrosion-resistant-wire cloth screening, it is also permissible to use hardware cloth, perforated vinyl, or any other similar material that will prevent unwanted entry. A cross-reference is also provided to IMC Chapter 7 to remind users that there are special requirements where combustion air is obtained from the attic area.

1203.4   Under-floor ventilation.   In order to ventilate the space below the building between the bottom of the floor joists and the ground, ventilation openings shall be provided through foundation walls or exterior walls. The provisions apply to areas such as crawl spaces, rather than occupiable areas such as basements. Under certain climatic conditions, it is possible to ventilate the under-floor space into the interior of the building, or continuously operated mechanical ventilation may be provided in lieu of ventilation openings where the ground surface is covered with an approved vapor retarder.

To properly determine the minimum net area of ventilation openings, at least 1 square foot (0.0929 m²) shall be provided for each 150 square feet (13.9 m²) of crawl space area. The openings shall be located so as to provide cross ventilation in the under-floor area. See Figure 1203-4. An exception permits a dramatic reduction in the amount of ventilation opening area, provided the ground surface is treated with Class I vapor-barrier material. In this case, the total area of ventilation openings need not exceed 1/1,500 of the under-floor area, provided such openings are located to provide for adequate cross ventilation of the under-floor space. In this case, the vents may have operable louvers.

Figure 1203-4   Under-floor ventilation.

It is critical that ventilation openings be completely covered with a substantial material to prevent the entrance of insects and animals. Corrosion-resistant wire mesh, with the least dimension not exceeding 1/8 inch (3.2 mm), is one of six materials identified by the code to address this concern.

Where the under-floor space is conditioned, it is unnecessary to provide ventilation openings. It has been shown that by insulating the perimeter walls, covering the ground surface with a Class I vapor barrier, and conditioning the space in accordance with the International Energy Conservation Code® (IECC®), unvented crawl spaces outperform vented under-floor areas.

1203.5   Natural ventilation.   Where buildings are not provided with adequate mechanical ventilation as specified in the IMC, natural ventilation through openings directly to the exterior must be provided. In order to determine the amount of ventilation air required, the minimum openable area to the outdoors is based on 4 percent of the floor area being ventilated.

In those cases where rooms or spaces do not have direct openings to the exterior, it is still necessary to ventilate the interior space, often through an adjoining room. In this case, the opening to the adjoining room should be unobstructed and have an area not less than 8 percent of the floor area of the interior room or space. In no case should the opening between the rooms be less than 25 square feet (2.3 m²). Where the intervening room is a thermally isolated sunroom or patio cover, the minimum openable area of 8 percent is still applicable; however, the opening need only be 20 square feet (1.86 m²).

As previously mentioned, in calculating the total openable area to the outdoors, such opening area shall not be less than 4 percent of the total floor area being ventilated. In those conditions where openings that provide the natural ventilation are located below grade, the outside horizontal clear space measured perpendicular to the opening is required to be at least one- and one-half times the depth of the opening.

Where rooms contain bathtubs, showers, spas, and similar bathing fixtures, natural ventilation is not an acceptable method. Because of the common reluctance to open exterior windows, particularly in cold-weather conditions, a mechanical system provides for more consistent ventilation. Therefore, bathrooms and similar spaces must be mechanically ventilated in accordance with the IMC. Where flammable and combustible hazards or other contaminant sources are present within an interior space, ventilation-exhaust systems shall be provided as required by the IMC and the International Fire Code® (IFC®).

Section 1204 Temperature Control

For those interior spaces where the primary purpose is associated with human comfort, it is important that a minimum indoor temperature of 68°F (20°C) can be maintained, measured at 3 feet (914 mm) above the floor on the design heating day. Although the code does not require that this temperature be constantly provided, it does mandate that such interior spaces be provided with equipment or systems having the capability of maintaining the desired temperature.

The exceptions recognize that there are conditions and occupancies where a mandate for space-heating systems is unnecessary. Requirements for Group F, H, and S occupancies are governed by OSHA regulations. In Group U occupancies, such space heating is not need, and in Group H occupancies it is often undesired.

Section 1205 Lighting

Almost every occupancy requires some level of lighting that is due to its use. Means of egress illumination is also required by Section 1008. In spite of the obvious need for interior light as a necessary part of a building’s function, the code mandates that some degree of lighting, whether artificial or natural, be provided to every occupiable space.

1205.2   Natural light.   Where glazing to the exterior is used as the method for providing natural light, the exterior openings shall open directly onto a public way, yard, or court in compliance with Section 1205. Exterior wall openings used to provide natural light must have an area that is computed based on the net glazed area for windows and doors, and not the nominal size of the opening. Where a room is not located on an exterior wall, the provisions of this section permit the borrowing of light from an adjoining room. Figure 1205-1 illustrates the requirements for this condition.

Figure 1205-1   Borrowing natural light.

Section 1206 Yards or Courts

The International Building Code® (IBC®) contains provisions for yards and courts where they are used to provide the required light and ventilation to exterior openings in the building. Most modern-day zoning ordinances also have requirements for yards and courts, and quite often these are more than adequate to gain the lighting and ventilation required by the code. In addition, where the alternatives of artificial light and mechanical ventilation as provided by Sections 1205.3 and 1203.1, respectively, are used in lieu of natural light and ventilation, the provisions of Section 1206 are not applicable.

To be considered providing adequate natural light and ventilation, each yard or court must have a minimum width of 3 feet (914 mm). In addition, these yards and courts must be increased in width, depending on the height of the building. See Figure 1206-1. The intent for the tall building is to have an increased court width so that light coming into the court will be able to reach the lower stories of the building, and this is only possible where the width of the court is in proper relationship to the height of the court. The requirements in the code are an obvious compromise between optimum light at the bottom of a court and the need to build as much building area on the lot as possible for economic purposes.

Figure 1206-1   Yards and courts.

Inner courts that are enclosed by the walls of the buildings, sometimes referred to as light wells, obviously need some means to remove accumulated trash at the bottom, provide for adequate drainage, and provide for circulation of air for ventilation purposes. In keeping with this intent, the code requires that an air intake be provided at the bottom of courts for buildings more than two stories in height, that grading and drainage be addressed, and that all courts be provided with access for cleaning.

Section 1207 Sound Transmission

Applicable only to buildings containing dwelling units and sleeping units, this section is intended to provide regulations covering sound transmission control. It pertains to wall and floor/ceiling assemblies separating dwelling units from each other and from public space, such as interior corridors, stairs, or service areas. These must be provided with airborne-sound insulation for the walls and both airborne- and impact-sound insulation for the floor/ceiling assemblies.

For airborne-sound insulation, the separating walls and floor/ceiling assemblies must be provided with insulation equal to that required for a Sound Transmission Class (STC) of 50 (45 when field tested) as defined by ASTM E 90. As an alternative for concrete masonry and clay masonry assemblies, the sound transmission class may be calculated per TMS 0302. Penetrations or openings through the assemblies must be sealed, lined, insulated, or otherwise treated to maintain the required ratings. Entrance doors only need to be tight fitting to the frame and sill. Floor/ceiling assemblies between separate dwelling units must also provide impact-sound insulation equal to that required to meet an impact insulation class of 50 (45 when field tested), as defined in ASTM E 492.

Although the scope of these provisions has historically been limited to apartment buildings and other residential structures containing dwelling units, the application of sound transmission controls is also applicable to all buildings containing sleeping units. Although this would include those vertical and/or horizontal elements separating hotel guest rooms and dormitory rooms, it also addresses sound separations between sleeping units in institutional facilities, such as hospitals, nursing homes, and assisted living facilities.

Section 1208 Interior Space Dimensions

Room size, tightness of construction, minimum ceiling height, number of occupants, and ventilation all interact with each other to establish the interior living environment insofar as odors, moisture, and transmission of disease are concerned. Therefore, the IBC regulates room sizes to assist in maintaining a comfortable and safe interior environment, and the minimum room sizes become increasingly important as buildings become even tighter in their construction because of energy-conservation requirements.

1208.2   Minimum ceiling heights.   Section 1208.2 regulates ceiling height, not only to assist in maintaining a comfortable indoor environment, but also to provide safety for the occupants of the building. As our population becomes increasingly taller, it is important that tall individuals be able to move about without striking projections from the ceiling with their heads.

The basic requirement is that the ceiling height be not less than 7 feet 6 inches (2,286 mm) for occupiable spaces, habitable spaces, and corridors (see definitions of occupiable space and habitable space in Section 202). Kitchens, halls, baths, and so on, may have a ceiling height less than 7 feet 6 inches (2,286 mm), but under no circumstances may such a height be less than 7 feet (2,134 mm) measured to the lowest projection from the ceiling.

For those ceilings within dwellings having exposed beams that project down from the ceiling surface, the ceiling beam members may project no more than 6 inches (152 mm) below the required ceiling height, provided the beams or girders are spaced at not less than 4 feet (1,219 mm) on center.

For rooms with sloped ceilings, the code requires only that the prescribed ceiling height be maintained in one-half the area of the room. However, no portion of the room that has a ceiling height of less than 5 feet (1,524 mm) shall be used in the computations for floor area. In the case of a room with a furred ceiling, the code requires the prescribed ceiling height in two-thirds of the area and, as in all cases for projections below the ceiling, the furred area may not be less than 7 feet (2,134 mm) above the floor.

1208.4   Efficiency dwelling units.   This section of the code provides for a specific type of dwelling unit—a dwelling unit consisting of only one habitable room. Many of the requirements in this section are redundant, as this chapter already requires many of these provisions. However, there are some requirements that are unique to the efficiency dwelling unit:

1.   The living room (which also serves as a bedroom and kitchen) is to have not less than 220 square feet (20.4 m²) of floor area. It is the intent of the code that this floor area be the total gross floor area, less the area occupied by built-in cabinets and other built-in appliances that are not readily removed and that preclude any other use of the floor space occupied by the built-in cabinets and fixtures.

2.   The minimum room size shall be increased by 100 square feet (9.29 m²) of floor area for each intended occupant in the unit in excess of two.

3.   A closet is required.

4.   A kitchen sink, cooking appliance, and refrigeration facilities are required, each providing a clear working space of not less than 30 inches (762 mm) in front.

5.   A separate bathroom containing a water closet, lavatory, and bathtub or shower is required.

Section 1209 Access to Unoccupied Spaces

Access to crawl spaces and attic spaces is regulated by this section. Though typically unoccupied, it is sometimes necessary that these normally concealed areas be accessed for various reasons.

1209.1   Crawl spaces.   This section of the code mandates that under-floor areas be accessible by a minimum 18-inch by 24-inch (457-mm by 610-mm) access opening. Where the access opening opens to the exterior of the building, the code intends it to be screened or covered to prevent the entrance of insects and animals. Also, it is the intent of the code that all portions of the under-floor area be accessible and access be provided beneath or around obstructions created by pipes, ducts, and so on.

1209.2   Attic spaces.   Because enclosed attics provide an avenue for the undetected spread of fire in a concealed space, the code requires that access openings be provided into the attic so that fire-fighting forces may gain entry to fight the fire. To be of any value, the access openings must be of sufficient size to admit a fire fighter with fire-suppression gear and must also have enough headroom so that entry into the attic may be secured. Although not specified, the access should be located in a readily accessible location. A public hallway is the best location for attic-access openings. Fire department personnel will not then have to open private offices, apartments, or hotel rooms in order to enter the attic. Attic access may be provided through a wall as well as through a ceiling. In split-level buildings with multiple attics, an attic-access opening must be provided to each attic space.

Attic access is only required by the IBC for those attic areas having a clear height greater than 30 inches (762 mm). Where such conditions occur, an attic-access opening of not less than 20 inches by 30 inches (559 mm by 762 mm) shall be provided. However, if the attic contains mechanical equipment, the opening may need to be enlarged to gain compliance with the IMC.

Section 1210 Toilet and Bathroom Requirements

The primary thrust of this section is to provide easily cleanable, sanitary, and water-resistant surfaces in toilet rooms and shower areas.

1210.2.1   Floors and wall bases.   Except for dwelling units, the code requires toilet room and bathing room floors to have a smooth, hard, nonabsorbent surface. Finishes such as concrete and ceramic tile are certainly acceptable, as are other approved materials that may also be used. It is the intent of the code that the building official determine the suitability of the proposed floor surface insofar as cleanability and water resistance are concerned.

Although the materials used for the floor covering and the wall base are to all have a smooth, hard, nonabsorbent surface, they can be of different materials. For example, a top set rubber base extending at least 4 inches (102 mm) up the wall is generally viewed as acceptable in conjunction with a floor covering of vinyl composition tiles.

Toilet and bathing room floor-finish requirements apply to all uses and occupancies except for dwelling units. Because motel and hotel rooms are typically not dwelling units, toilet room flooring in these uses must often comply with this section.

1210.2.2   Walls and partitions.   Walls and partitions within 2 feet (610 mm) of the front and sides of urinals, water closets, and service sinks are required to have a smooth, hard, nonabsorbent finish. Required finishes shall extend to a height of at least 4 feet (1,219 mm) above the floor and shall be of a type not adversely affected by moisture. Materials used as a base for tile or wall panels must satisfy the limitations set forth in Section 2509. Although the code does not specifically state that concrete walls must be sealed, concrete is not, strictly speaking, a nonabsorbent material and needs some type of surface treatment. Sealing is particularly important for concrete block walls.

Special wall finishes at water closets and urinals are not required for dwelling units, sleeping units, and toilet rooms not accessible to the public that contain only one water closet. Note that the exceptions for floor finishes and wall finishes are not the same. A private toilet room containing one water closet would be required to have flooring that complies with Section 1210.2.1, but there would be no special requirements for wall finishes.

In all occupancies, including dwelling units, penetrations of the water-resistant surfacing of the walls for the installation of accessories such as grab bars, towel bars, and so on, are required to be sealed to protect the structural elements from moisture. The intent of the code is that because the structural elements are not required to be moisture resistant, the penetrations should be sealed to protect the structural elements. Although sealing is required for all walls in a toilet room, sealing is obviously most critical in areas of water splash such as in showers or behind or adjacent to lavatories.

1210.2.3   Showers.   All showers must have floor and wall finishes that are smooth, nonabsorbent, and not affected by moisture. Wall finishes must extend not less than 72 inches (1,829 mm) above the drain inlet.