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The ground plane is the most fundamental element of interior design. It’s the surface that supports all the activities, construction, and furnishings that make up any interior space. As a basic enclosing surface, the ground plane, like the overhead plane, represents a significant percentage of the total surface area defining any room or space. It not only provides structural support and a walking surface but also contributes significantly to the character and definition of the interior environment.

The ground plane must remain flat and level. Unlike walls, ceilings, furniture, and other interior elements that can be angled, curved, and irregular, a floor must essentially be a smooth surface, with only occasional interruptions with ramps or stairs. The interior designer must express any design statement with material, color, pattern, shape, or a change in level.

Floors support two types of elements, fixed and movable. Fixed elements include construction such as partitions, cabinetry, and other raised floors. Movable elements include furniture, equipment, and temporary constructions. Fixed elements generally are perceived as part of the architecture of a space, while movable elements read as furnishings.

The ground plane can be a neutral background for furniture and other elements or it can be a major design statement in itself. The texture, color, and shapes of the flooring material can also change the scale and character of the space in which it’s used.

The interior designer can use the ground plane as a major design element, while meeting all of the functional requirements of support, safety, durability, and accessibility. This section discusses some of the design concepts that the designer can use to begin thinking of the ground plane as a significant element and gives some practical starting points for detailing.

Refer to Section 11 for more ideas on how to make transitions between ground planes.

---- Ground plane concepts (a) none (b) directional (c) directional, off grid (d) simple line division (e) dynamic line (f) island (g) line (h) pattern (i) pattern within pattern (j) coordinate with overhead (l) coordinate with furniture (k) contrast with overhead

--- Stair placement concepts (a) extended (b) recessed (c) parallel (d) full length (e) shaped (g) wrap around upper lower upper lower upper lower upper lower upper lower upper lower upper lower upper lower upper lower upper lower upper lower upper lower (h) offset (j) splayed (k) angled splayed (i) angled straight (f) recessed fan (l) half splay


Because of the planar nature of floors and the strict needs for safety, accessibility, and other functional requirements, there are fewer possible structural concepts that the designer can use than might be possible with the ceiling plane or with vertical barriers. However, even with these limitations, the designer can develop a strong design statement by using flooring creatively and in conjunction with the ceiling plane, vertical barriers, changes in level, and other built-in construction.


When sufficient space is not available for changes in level, the designer can use the material, color, texture, and line of flooring materials as well as changes of these elements within a single plane to express the design intent of the space. --- shows some of these basic approaches.

Of course, the simplest approach is to use a single material as a background for the activities, furniture, and other construction within the space. The flooring material can be plain, textured, neutral, or boldly colored. The flooring can have a strong directional line which can affect the dynamic, proportion, and scale of a space.

However, as with ceiling patterns, a strong directional pattern should be run perpendicular to the length of a space. Large patterns should generally be used with large spaces and small patterns with smaller spaces. Small patterns in a large space will sometimes be perceived as an overall tone rather than individual visual texture.

Changes in material can be used to define space or for functional reasons. E.g., hard surface flooring may be required next to carpet for durability in a high-traffic area or for water resistance next to wet areas. The material changes may be made with a simple line or more complex patterns.

Special patterns can also be designed as a design feature or to direct movement. Flooring variations in a single plane are even more effective when coordinated with changes in ceiling plane or material or used in conjunction with furniture groupings. Although islands of different flooring can also be created with area rugs, these may present a tripping hazard and may be difficult to maintain in commercial uses.

The ground plane can be used most effectively to define space when a level change is possible. Of course, this requires sufficient ceiling space, but even a slight rise is sufficient to create a noticeable difference and create the effect desired. In addition to the change in level itself, the line of transition can be treated in various ways.

The designer can use stairs or ramps alone to make the transition or simply have the change in level interrupted with railings or other features.


Of course, when there is a change in level, the designer must provide a way to move from one level to the other. This requires steps and usually an adjacent ramp. Moving up and down just a few inches or a few feet within a space requires a different design response than moving from one floor level to another. Although there are some similar requirements of safety and comfort, floor-level changes often require stairs that meet egress requirements, while minor level changes are usually considered monumental stairs. This section only discusses small changes in level requiring one to five steps as might be used for a small level change.

One of the first decisions the designer must make is the height of the level change and the number of steps. Although a platform with a single step up is the easiest and least expensive to construct, single steps are inherently dangerous and should usually be avoided. However, with careful design and inclusion of handrails and visual clues identifying the level change, single-step level changes may be used.

--- illustrates some of the ways short runs of steps can placed relative to the level changes they serve. Straight, relatively narrow stairs are the most efficient and safest. Wide stairs extending the full length of the level change, create more of a design feature and allow movement over a wider area. Wide stairs may require intermediate handrails for safety. Refer to the later section in this section on constraints for a discussion of code requirements. These types of stairs can be made safer by extending the depth of the tread beyond the code minimum of 11 in. (279 mm).

Although stairs can be curved in plan or wrapped around an angle, these are inherently more dangerous and should be used carefully with sufficient handrails and nosing marking.. Other variations can be used. These provide a variation in the straight run of stair but still provide for a walk path perpendicular to the width of the stairway, which is safer than walking at an angle to each tread. Splayed forms can be used to direct movement either at the top or bottom of the stair.


Accessibility codes generally require ramps be provided for any change in level. They may be used alone or in conjunction with steps. Because ramps require significant amounts of floor area, the designer typically limits the height of an optional platform created strictly for design reasons to minimize the length of ramp required. However, in some situations the length along a ramp may be used for other purposes. E.g., in a retail store, a display may be built next to one side of a ramp, so the ramp serves for both circulation and merchandising.

--- illustrates some of the conceptual ways ramps can be placed relative to level changes and in conjunction with steps. In most cases, especially in public areas, both stairs and ramps should be provided. Some people with mobility problems find it easier to use stairs than walk a longer distance along a ramp. Ideally, the starting and ending points of both stairs and adjacent ramps should be in the same area.

The designer should decide on how to place stairs and ramps based first on the height the ramp must serve. A 21 in. (533 mm) level change will require a much longer ramp than a 7 in. (178 mm) change, which may require a switchback con figuration rather than a straight run.

--- Ramp placement concepts (a) extended (b) recessed (c) full length (f) parallel, with stairs (e) full length, with stairs (i) adjacent upper lower upper lower upper lower upper lower upper lower lower upper lower (d) parallel, ramp only upper lower upper lower upper lower upper lower upper lower upper note: diagrams not to scale (g) separated upper ends (h) switchback (j) wrap around (k) angled (l) switchback extended


More than any other design element, the ground plane requires the most attention to its functional requirements. The floor of any space must provide a stable, safe means of movement for people and a structurally sound platform for furniture and other construction. Because of the amount of use the floor experiences, it must also be durable for the type of use it’s put to and relatively easy to clean and otherwise maintain. The ground plane should also provide the desired sense of movement and control of circulation. Some of the other functional requirements include accessibility for all users, comfort, water resistance, and sustainability.

Regardless of the approach the designer may take with the ground plane, these functional requirements must be met. Refer to Sections 2 and 3 for further discussion of basic constraints and functional requirements of details.


For the ground plane, constraints typically include the fire resistance of the finish floor material and its support as well as the structural integrity and safety of the floor. For changes in level, code requirements for safety and accessibility must also be considered.

Fire Resistance of Floor Finishes

The IBC regulates the use of some finish flooring materials. These include textile coverings or those composed of fibers, which is mainly carpet. The IBC specifically excludes traditional flooring such as wood, vinyl, linoleum, terrazzo, and other resilient floor coverings that are not composed of fibers.

The IBC requires textile or fiber floor coverings to be one of two classes as defined by NFPA 253, the Flooring Radiant Panel Test. The NFPA 253 test measures the flame spread in a corridor or exitway that is under the in fluence of a fully developed fire in an adjacent space.

Class I materials are more resistant to flame spread than Class II materials.

In Groups I-1, I-2, and I-3 occupancies (such as assisted living facilities, hospitals, nursing homes, and jails) the flooring finishes in exit enclosures (stairways), exit passageways, and corridors must be Class I in a non-sprinklered building and at least a Class II in a sprinklered building. Practically, because the IBC also requires all I occupancies to be sprinklered, either Class I or Class II is permissible. In other areas of Groups I-1, I-2, and I-3 occupancies, the flooring must be a Class II material.

For all other occupancy groups, the IBC requires that textile floor coverings be a Class II material in nonsprinklered buildings. In sprinklered buildings, textile flooring must meet the requirements of 16 CFR Part 1630, Standard for the Surface Flammability of Carpets and Rugs.

This is also known as the methenamine pill test or simply the pill test. It’s also referred to by other designations, DOC FF-1, Standard Test Method for Flammability of Finished Textile Floor Covering Materials and ASTM D2859, Standard Test Method for Ignition Characteristics of Finished Textile Floor Covering Materials. All carpet sold and manufactured in the United States must pass the pill test.

Because all carpet in the United States must pass the pill test and because nearly all manufacturers of resilient and hard-surface materials provide products that meet a Class I or II classification, specifying finish flooring is usually not a problem when detailing platforms, stairs, and ramps.

Fire Resistance of Structural Flooring Components

In addition to finishes, the IBC regulates the types of materials that can be used to construct raised platforms, stairs, and ramps. These are classified generally as combustible or noncombustible. Combustible materials include wood, while noncombustible materials include steel framing, concrete, and masonry.

For the purposes of fire and life safety, buildings are classified into one of five categories, Type I, II, III, IV, or V. The classification is based on the fire resistance of certain building components such as the structural frame, bearing walls, floor construction, and roof construction. Type I construction is the most fire resistive, and Type V is the least fire resistive. E.g., the structural frame of a Type I building must have a 3-hour rating, while the frame in a Type III building must only have a 1-hour rating. In combination with occupancy groups, building type limits the area and height of buildings. Homes and small, one to three-story buildings are typical of Type V construction.

In Type I and Type II construction, any sub floor framing must be noncombustible or the space between the fire-resistant floor of the building and the platform, stair, or ramp must be solidly filled with noncombustible materials or fire-blocked in accordance the IBC. Refer to the IBC for more information on construction types and detailed requirements.

Some jurisdictions may allow the use of fire-retardant-treated wood to build low platforms or stairs in Types I and II buildings. In all cases, the interior designer should verify the type of construction and the requirements of the local authority that has jurisdiction before detailing level changes and stairs and ramps.

There are special requirements for wood finish flooring in Type I and Type II buildings.

Wood flooring may be attached directly to embedded or fire-blocked wood sleepers or directly cemented to the top of the fire-resistant structural floor. Wood flooring can also be attached to wood framing if it meets the requirements described in the preceding paragraph. For Types III, IV, and V buildings, wood framing may be used for any type of floor.

Refer to Section 2 for more information on fire tests for finish materials and construction assemblies.

--- Accessible ramps max. 30" (760) max. 30' (9140 mm) curb or barrier landing 60" (1525) min. ; 12" (305) min. level handrail extension 34"-38" (865-965) 34"-38" (865-965) handrail level handrail extension handrail continuous if ramp continues (a) schematic ramp elevation (b) edge protection options extended floor curbs rail barrier 12 1 12" (305) min.

4" (100) min.

< 4" (100) 36" (915) min.


Slip Resistance and Tripping

Two common safety problems with ground surfaces are slipping and tripping. All surfaces should have slip resistance appropriate for the use. E.g., the floor of a public lobby where snow and water are tracked in should be more slip resistant than a private office. As discussed in Section 2, slip resistance is commonly measured by the coefficient of friction (COF) and is a number ranging from 0 to 1. A COF of 0.5 is considered a minimum value for floors. For accessible routes a COF of 0.6 is recommended for level interior surfaces and 0.8 for ramps. Refer to Section 2 for more information.

Tripping on level surfaces generally occurs because of a slight change in level between two different materials or between the same materials installed, so the edges are not flash.

When two materials abut, the designer should detail the joint so that the two surfaces are as flash as possible. ADA requirements for accessibility limit any change in level with a vertical surface to 1/4 in. (6.4 mm). A change in level of up to 1/2 in. (13 mm) may be 1/4 in. (6.4 mm) vertical and 1/4 in. (6.4 mm) beveled with a slope not steeper than 1:2 (13 mm); that is, 1/4 in. (6.4 mm) high and 1/2 in. (13 mm) horizontal. Further, ADA requirements limit the pile height of carpet to a maximum of 1/2 in. (13 mm) measured from the top of the carpet to the backing. Ideally, there should be no vertical changes in level from one material to another with all changes made with sloped or beveled surfaces or transition materials. See ---- for details of some transitions.


In addition to the accessibility requirements for floor surfaces stated above, the designer must also consider other accessibility issues when detailing ramps and stairs.

Ramps cannot slope more than 1 unit in height for every 12 units in length. Thus, a ramp rising 14 in. (356 mm) must be at least 14 ft. (4267 mm) long in horizontal projection.

However, whenever possible ramps should be designed with a slope less than 1:12, both to make it easier for people to use and also to allow for any construction tolerances when the ramp is constructed.

Ramps must be at least 36 in. (915 mm) wide between handrails. Handrails must be provided on both sides of the ramp when the rise is greater than 6 in. (150 mm). Level landings are required at the top and bottom of each ramp run. The landing must be at least as wide as the width of the ramp for straight runs and at least 60 in. (1525 mm) square when the ramp turns 90 degrees or at least 60 in. (1525 mm) deep at a switchback. Other requirements for accessible ramps are shown.

---- Stair requirements 11" (279) min.

4" (102) min.

7" (178) max.

34"-38" (864-965) note: IBC SI equivalents are slightly different than ADA requirements due to rounding 12" (305) min.

TT guard on open stairs min. 42" (1067) above nosing handrail returned to wall, to newel post, or floor

-- Code Requirements

Building codes regulate the type, number, and width of egress stairways as well as detailed requirements for treads, risers, and handrails. Most of these are part of the architecture of a building. However, for the types of stairs described in this section that consist of only a few risers and are often detailed by interior designers, the code requirements for step design and handrails still apply.

In most cases, the IBC requires handrails on both sides of stairs. The exceptions for interior use include the following:

_ Aisle stairs in some situations

_ Stairways in dwelling units

_ Spiral stairways

_ Single risers in Group R-3 occupancies

_ Changes in room elevation of three or fewer risers within dwelling units and sleeping units in Group R-2 and R-3 occupancies ( E.g., apartments, dormitories, and non-transient hotels, and occupancies where the occupants are primarily permanent in nature not otherwise classified as R-1, R-2, or R-4) However, even if handrails are not required, they should be provided for safety and convenience.

The basic requirements for stairways and handrails are shown. The ends of handrails must return to a wall, guard, or the walking surface or be continuous to the handrail of an adjacent stair flight (or ramp run in the case of ramps). Refer for more guidelines on stair design.

On open stairways, the IBC requires that a separate guard or low wall, in addition to the handrail, be provided at 42 in. (1067 mm) above the height of the nosing. The guard must be solid or designed so that there are no openings that allow the passage of a sphere 4 in. (102 mm) in diameter. Refer to the IBC for exceptions to this requirement.

The issue of where handrails are required for monumental stairs (those not required for egress) can be confusing and sometimes contradictory. Of course, handrails should always be located on each side of any stairway. When the width of the stairway exceeds 60 in. (1524 mm), the IBC requires intermediate handrails such that all portions of the stairway width required for egress capacity are within 30 in. (762 mm) of a handrail. Thus, a wide stair that serves a small occupant load for egress purposes may not need intermediate handrails.

E.g., assume that a wide monumental stair serves a raised platform on the first floor of a retail store and has handrails on both sides. Each handrail would be within 30 in. (762 mm) of egress width for a total of 60 in. (1524 mm). The IBC requires a minimum egress width for stairways of 0.3 in. (7.63 mm) per occupant served or, minimum width (inches) = occupant load × 0.3in.

Knowing that 60 in. is available the maximum occupant load that can be served by these two handrails is, 60 in. = occupant load × 0.3in./occupant max. occupant load = 60 in. 0.3in./occ. max. occupant load = 200 occupants If the platform serves fewer than 200 occupants an intermediate handrail would not be required. For a mercantile occupancy on the first floor, the IBC states a maximum floor allowance per occupant of 30 sq. ft. In terms of a formula, occupant load = floor-area 30 sq. ft./occ.

If the maximum occupant load for the handrails is 200 then, 200 occupants = floor area 30 sq. ft./occ.

max. floor area = 200 × 30 max. floor area = 6000 sq. ft. (557 m^2).

Thus, the platform could be up to 6000 sq. ft. in area before intermediate handrails would be required. However, the IBC also requires that monumental stairs have handrails located along the most direct path of egress travel. The issue then would be whether the sides of the stairway are along the most direct path. This can be subject to interpretation. When the issue is questionable, the designer should consult with the authority having jurisdiction for the required location of intermediate handrails.

Handrails should be designed so that people can both grip them with maximum effect and hold them by friction when pulling up or descending. A circular shape with a diameter of 1-1/2 in. (38 mm) is generally the best, but other shapes are allowed. See ---- for the allowable limits on handrail profiles according to the IBC. The Type II handrail shown in (b) is allowed in private homes and in selective residential situations in commercial applications.

---- Sub floor Tolerances Required for Finish Floors Finish Floor Material Required Sub floor Tolerance Wood flooring strip flooring and parquet flooring wood sub floor: 1/4 in. in 10 ft. (6 mm in 3 m) strip flooring and parquet flooring concrete sub floor: 1/8 in. in 10 ft. (3 mm in 3 m) cushioned flooring concrete sub floor: 3/16 in. in 10 ft. (5 mm in 3 m) laminated flooring concrete sub floor: 1/8 in. in 10 ft. (3 mm in 3 m) mastic cushioned concrete sub floor: 1/4 in. in 10 ft. (6 mm in 3 m) steel channel concrete sub floor: 1/8 in. in 10 ft. (3 mm in 3 m) Ceramic tile portland cement mortar bed 1/4 in. in 10 ft. (6 mm in 3 m) dry-set or latex-portland cement mortar, thin set 1/4 in. in 10 ft. (6 mm in 3 m) organic adhesive or epoxy adhesive 1/16 in. in 3 ft. (2 mm in 1 m) with no abrupt irregularities more than 1/32 in. (0.8 mm) Stone flooring stone tile wood sub floor: 1/16 in. in 3 ft. (1.6 mm in 900 mm) stone tile on thin bed mortar concrete sub floor: 1/8 in. in 10 ft. (3 mm in 3 m) Terrazzo concrete sub floor: 1/4 in. in 10 ft. (6 mm in 3 m).


Flooring design and detailing must be coordinated with flooring tolerances, light reflectance and acoustic requirements, durability needs, and desired circulation patterns. In addition, the design of the ground plane should be coordinated with the overhead plane and how the connections between the floor and the partitions are made. Refer to Sections 7 and 10 for design ideas on overhead planes and how to make the floor-to-wall transition.

Tolerance Coordination

When carpet is used, the flatness tolerance of the sub floor is typically not a concern. However, when hard-surfaced finish flooring is specified, the sub floor on which it’s placed must be within certain tolerances for a successful installation.

Some industry-standard tolerances for sub flooring are given. ---- lists some requirements for the installation of finish flooring. In many cases, existing sub flooring may exceed the requirements for a successful installation and the interior designer will need to develop details or specifications to have the sub flooring brought into compliance with finish flooring requirements. If this includes using a leveling compound, the finish surface may be raised higher than adjacent flooring. Grinding or patching existing sub floors will increase costs. In new construction, the interior designer may coordinate with the architect to create recessed areas for thick flooring material before the floor is constructed to minimize this problem.

Light Reflectance and Acoustic Coordination

For lighting design, the r eflectance of the ground plane is generally the least important surface, coming after the ceiling and the walls. This allows the interior designer to specify nearly any color and texture for the floor finish without adversely affecting light quality.

The floor's sound absorption can significantly affect the overall acoustic quality of the space and should be selected with care. A hard-surface floor, such as wood or resilient tile, will both r eflect sound and increase the sound transmission to the floor below, both of which may be undesirable. E.g., the sound absorption average (SAA) (similar to the older NRC or noise reduction coefficient) of 1/2-in. pile carpet on padding is about 0.50, while the SAA of wood flooring is about 0.10. This means that carpet will absorb five times the sound of the wood flooring in certain frequency ranges. Likewise, footfalls on wood flooring can be easily transmitted to the floor below. If this is unacceptable, other detailing options (such as sound-deadening board) must be used to minimize the sound transmission, increasing cost and detailing complexity. Using carpet would be a simpler approach.


Detailing flooring material on concrete or wood substrates is usually straightforward. The main detailing concerns for flooring other than carpet are accommodating the total thickness of the finish material, making transitions from one material to another, and allowing for tolerances and movement of the sub floor. If terrazzo or thick-set tile or stone is used the ability of the floor to carry the additional weight must be verified with a structural engineer.



For most commercial and residential applications either wood strip flooring or thin parquet or laminated flooring is used. Other types of wood flooring, such as plank, block, and resilient floor systems are not discussed in this section.

Wood strip flooring is installed over a suitable nailing base by blind nailing through the tongue of each strip of tongue-and-groove strip. ---- shows the typical methods of detailing wood strip flooring over both wood and concrete floors. For wood structures, the sub floor should plywood, particleboard, or other suitable underlayment with a minimum thickness of 1/2 in. (13 mm). A layer of 15 lb. asphalt felt may be laid to prevent squeaking and act as a vapor barrier.

For concrete structures, either of the two methods may be used. Placing the floor on wood sleepers gives a more resilient floor and provides an air space that allows excess moisture to escape. However, it requires more space and can be problematic when installing it next to a thinner floor. The method, using a 3/4 in. (19 mm) thick plywood or particleboard base, requires less total height but can still pose problems when abutted to much thinner flooring such as resilient tile. In all cases it’s important to provide a minimum 3/4 in. (19 mm) expansion space at the perimeter of the room to allow for expansion and contraction of the flooring.

Parquet and laminated flooring can be glued or loose laid over wood or concrete sub floors. However, when such flooring is placed on a concrete sub floor, especially a slab on grade, it’s critical that moisture not be present and the slab be level to within 1/8 in. in 10 ft. (3 mm in 3 m).

--- Wood strip flooring 2 x (38) joist wood base partition min. 5/8" (16 mm) plywood or oriented strand board 15 lb. asphalt felt or building paper, loose laid provide 3/4" (19) minimum expansion space blind nail wood base partition blind nail concrete slab provide 3/4" (19) minimum expansion space (a) flooring on wood subfloor (b) flooring on concrete (c) flooring on sleepers on concrete 3/4" x 2 1/4" (19 x 57) tongue and groove flooring 3/4" x 2 1/4" (19 x 57) tongue and groove flooring 3/4" (19) plywood laid loose with 1/4" to 1/2" (6 m to 13 mm) gap between panels wood base partition 6 mil polyethylene 3/4" (19) expansion space 3/4" x 2 1/4" (19 x 57) tongue and groove flooring 2" x 4" (50 x 100) wood sleepers @ 12" o.c., random lengths; set in asphalt mastic, stagger end joints 4" (100)

--- Thin wood flooring (b) parquet flooring on concrete (c) laminate flooring (a) parquet flooring on wood subfloor closed-cell foam backing wood base laminate flooring partition provide 1/4" (6) to 1/2" (13 mm) min. expansion space new or existing subfloor mastic wood base partition provide 3/4" (19) minimum expansion space provide 3/4" (19) minimum expansion space parquet flooring mastic parquet flooring min. 1/2" (13 mm) plywood or particleboard with an underlayment or a combination subfloor underlayment

--- Ceramic tile flooring 2 x (51) joist 16" (400) o.c. 1 1/4" (32) concrete subfloor 3/4"- 1" (19-25) plywood or particleboard with an underlayment or a combination subfloor underlayment dry-set or latex-portland cement mortar portland cement mortar tile grout tile grout ceramic tile ceramic tile glass mesh mortar unit welded wire fabric antifracture membrane (a) tile on wood subfloor (b) tile on full mortar bed over concrete

-- -- Stone flooring concrete slab (a) thin set on concrete subfloor adhesive (b) thin set on wood frame subfloor (c) full mortar bed on concrete subfloor 1 1/4" (32) concrete subfloor

±1/2" (13)

±1/2" (13) stone flooring dry-set or latex-portland cement mortar stone tile stone flooring portland cement mortar welded wire fabric anti-fracture membrane


Ceramic tile or quarry tile must be laid over a suitable substrate using one of several formulations of mortar, or with adhesive. The joints are filled with grout. Refer to Ceramic Tile: The Installation G uide by the Tile Council of North America for a complete description of all the tile-setting methods. The two basic methods of detailing are the thin-set method and the full-mortar-bed method. Both of these are shown.

With the thin-set method tile is laid on a suitable substrate, commonly a glass mesh mortar unit specifically manufactured for tile installation. This is a cementitious panel nailed to the sub floor. The tile is then laid on a thin coating of dry-set or latex-portland cement mortar.

The sub floor must be rigid to prevent cracking.

When excessive d eflection is expected (more than about 1/360 of the span) or on precast and post-tensioned concrete floors, a full-mortar-bed detail should be used. With this method, the tile and reinforced mortar bed are separated from the structural floor with an antifracture membrane to allow the two floor components to move independently. In addition to providing for movement, this system allows minor variations in the sub floor level to be corrected with the mortar. This is the preferred method (along with a waterproo fing membrane) for tile floors in commercial showers or where continuous wetting will be present. Because of the overall thickness required, this is one finish flooring detail that should be placed on a sub floor depressed about 1-1/2 in. (38 mm), if possible.

With both the thin-set and full mortar bed methods of tile installation, it’s important to provide for movement joints to prevent or control cracking. Movement joints (sometimes called expansion joints) are required for large expanses of tile and where the tile abuts re straining surfaces, such as at columns, walls, and pipes. They are also required where backing materials change and where dissimilar floors occur. They are not required in small rooms or corridors less than 12 ft. (3660 mm) wide. ---- illustrates one type of tile movement joint, and ---- gives the recommended joint widths and spacing.

--- Terrazzo flooring concrete slab construction joint control joint 1/2" (13) (a) monolithic terrazzo floor 3/4" (19) terrazzo 1" or 1 1/2" (25 or 38) radius (b) monolithic terrazzo base zinc, brass, or plastic divider strip, T- or L-shape zinc, brass, or plastic divider strip, T- or L-shape 1/2" (13) monolithic terrazzo


Like ceramic tile, stone flooring can be installed with either the thin-set method or the full-mortar-bed method. The full-mortar-bed method, while much heavier, is used when the sub floor is uneven, where excessive d eflection or movement is expected, or when the stone varies in thickness, as with slate or sandstone. For most installations, current cutting and fabrication technology make it possible to use thin tiles of natural stone rather than the traditional 3/4 in. (19mm) thick stone on a full mortar bed. However, for thin-set applications, the floor must be level as given and not subject to d eflection or movement more than about 1/720 of the span.

--- shows three methods of placing stone flooring on wood and concrete floors.

With the thin-set method, a uniform thickness of stone is set on the sub floor with a special thin-set mortar or with an adhesive. The total thickness is about 1/2 in. (13 mm) depending on the thickness of the stone tile. The full-mortar bed method requires a layer of mortar from 3/4 in. to 1-1/4 in. (19 mm to 32 mm).

Stone floors can be set with the joints tightly butted together or with spaces between joints. If there is a gap in the joint, it must be filled with grout or a portland cement/sand mixture that can be color-coordinated with the stone. Several types of grout are available that are resistant to chemicals, fungi, and mildew. Latex grout is available and provides some flexibility when slight movement in the floor is expected.


Terrazzo is a composite material that consists of marble, quartz, granite, or other suitable stone chips in a matrix that is cementitious, modified cementitious, or resinous. It’s typically poured in place but can also be precast. Terrazzo is generally not detailed and specified by interior designers as a finish material. Because of the additional weight and thickness required, it’s usually part of the architecture of the building. It’s also messy to install and requires time for pouring, curing, and grinding to complete the process. However, terrazzo can be precast to avoid much of the on-site work required of standard installations. Terrazzo does provide a very durable floor and the colors and styles of the mixture can be varied between areas enclosed by the divider strips. It’s also possible to design very ornate patterns using curved divider strips and different color stone matrices.

There are various types of terrazzo installation methods, including the sand cushion, bonded, monolithic, and thin-set methods. The sand cushion and bonded methods are very heavy and require total installation thicknesses up to 2-1/2 in. (64 mm) thick. These are usually designed as part of the original architecture of a building.

Monolithic terrazzo installations are applied directly to a concrete sub floor, as shown. Terrazzo bases can be poured at the same time and provide a cove base. This type of terrazzo installation is about 1/2 in. (13 mm) thick and weighs about 7 lb. per ft^2 (3.4 kg/m2). The sub floor must be structurally capable of supporting the extra weight without excessive d eflection. Divider strips must be placed to provide areas of approximately 200 ft^2 to 300 ft^2 (19 m^2 to 28 m^2 ) in rectangular areas. The area of each area should not be more than 50% longer than the width. Joint location should be coordinated with building joints.

Thin-set terrazzo is similar to monolithic but only requires from 1/4 in to 3/8 in. (6 mm to 10 mm) thickness and weighs about 3 lb. per ft^2 (1.5 kg/m^2 ). Thin-set terrazzo must use epoxy, polyester, or poly-acrylate matrices with special types of divider strips.

--- Flooring transition strips edge divider snap down trim tile/carpet divider reducer transition edge round edge varies, 1/8"-1/2" (3-13) varies, 3/16"-3/4" (5-19) 1/8" (3) varies.


Interior Railing Manufacturers | Manufacturer Web Site | Comments American Railing Systems Aluminum and stainless steel with standard selection of picket or glass in fill ATR Technologies, Inc. Aluminum tube railings with picket or glass in fill; custom designs offered Big D Metalworks Stainless steel and wood systems with glass and perforated metal in fill panels Blumcraft Glass rail systems with metal and wood caps.

Including lighted rail systems and wall mounted handrails Construction Services, Inc. Custom railing and handrail systems in a variety of materials and styles C.R. Laurence Company Glass railing systems Hollaender Manufacturing Tube railing systems with pickets, wire mesh, and perforated metal in fill Livers Bronze Co. Variety of railing systems with metal and wood with glass, picket, and rail in fill; contemporary and traditional Newman Brothers, Inc. Metal and wood railing systems with glass in fill P&P Artec Stainless steel railings with picket or glass in fill RamiDesigns Stainless steel railing systems with picket, rail, and glass in fill The Wagner Companies Variety of contemporary and traditional styles in all materials

---- Transition Strip Manufacturers | Manufacturer Web Site Comments Ceramic Tool Company Edge, joint, bar, and carpet trim, and ramp transitions Genotek Wide variety of carpet trims, reducers, edge dividers, thresholds, movement joints, and transition edges, including adjustable transitions Johnsonite Transitions in a wide variety of colors for various thicknesses and material types, including reducers, edge guards, T molding, adaptors, wheeled traffic transitions, and expansion joint seals as well as stair treads and nosing strips National Metal Shapes Variety of trim shapes and styles in metal and vinyl for all flooring materials Schluter Systems Provides a wide variety of products for different materials and material thicknesses.


Whenever one flooring material abuts another on the same level, there must be some type of transition to prevent damage to the edges and to hold them secure. This is true whether they are the same type of material or different materials. As discussed there are three basic ways of making floor transitions: by simply abutting the two materials, by placing a protective edge between them, and by using a third material as a transition strip.

Abutting two materials without an intermediate material usually only works when the two materials are the same type and are relatively hard. E.g., two different types of stone flooring can be successfully abutted with a simple grout joint as long as the finish surfaces are flash. Stone can be placed next to ceramic tile with the same conditions. Conversely, the seam of two different types and pile heights of carpet is susceptible to damage unless a transition strip is placed over it.

Some type of protective edge is usually required when two materials abut. This can be as simple as a metal angle or a manufactured transition strip designed for specific types of flooring. (a) shows the application of a protective edge angle. Refer to ---- for common sizes of stainless steel and brass shapes that can be used to protect the edge of wood or stone flooring.

There are many types of manufactured wood, plastic, and metal transition strips made for various materials and material thicknesses. --- shows some common transition strips.

Refer to ---- for a listing of some of the manufacturers of transition strips. Most resilient and wood flooring manufacturers supply their own line of transition strips.

The designer can also detail custom transition strips and make them a design feature between two flooring materials. These types of strips can be beveled to accommodate the thicknesses of the flooring and made any convenient width. See (b) and (c) for two different types of floor transition details using a separate transition strip. The details show a beveled stone strip but hardwood transition strips can also be used.

Handrails, Guards, and Stairways

As discussed in a previous section of this section, handrails are required on both sides of all stairways used for egress and on monumental stairs if they are used for egress. They should also be provided wherever needed for safety. --- shows the basic requirements for handrail design. In addition, the handrail design on an open stair as well as guards cannot allow the passage of a 4 in. (102 mm) sphere. Guards are only required if the change in elevation exceeds 30 in. (762 mm), but they should be used in all situations for safety.

When a change in level occurs the transition can be made in a number of ways as discussed. The interior designer can detail custom railings and guards from wood, metal, or some combination of materials. However, in most cases, standard manufactured railing systems are used. These are available in a variety of styles and materials and are custom modified by the supplier to fit the exact requirements of the project. ---- lists some of the many manufacturers of railing systems while ---- lists manufacturers of cable rail systems.

Guards can be designed with wood or metal top rails and with in fills of glass, pickets, horizontal rails, mesh, perforated metal, or solid panels. All-glass railings may be used with a top rail or without a rail for an open appearance while providing for safety. See --- for one type of glass guard detail. This detail can also be used for stairways with the addition of a handrail.

Stairs must be provided for raised platforms more than 7 in. (178 mm) high. For most interior design work in spaces with low ceilings platform height is limited, requiring only two or three steps. These are easily constructed of wood or metal framing. Refer to Section 3 for guidelines on stair design.


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