Cover Page

Interior Design


4th Edition

A sketch depicting the interior design of rooms and hall.

Francis D. K. Ching • Corky Binggeli

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We spend the majority of our lives indoors, in the interior spaces created by the structures and shells of buildings. These spaces provide the physical context for much of what we do, and give substance and life to the architecture that houses them. This introductory text is a visual study of the nature and design of these interior settings.

The purpose of this primer is to introduce to students of interior design those fundamental elements that make up our interior environments. It outlines the characteristics of each element and presents the choices we have in selecting and arranging them into design patterns. In making these choices, emphasis is placed on basic design principles and how design relationships determine the functional, structural, and aesthetic qualities of interior spaces.

This fourth edition retains the organizational scheme of the third edition, with text and illustrations updated and added to cover sustainability standards, resource usage, and recent developments in the design of interior spaces. The section on lighting reflects current design practice, lamp and fixture styles, especially the growing use of light-emitting diodes (LEDs). The coverage of furnishings responds to changes in the work environment. New residential topics include accessory dwelling units (ADUs) and touchless kitchen faucets, among others. Standards and codes incorporate current International Code Council (ICC) and Americans with Disabilities Act (ADA) requirements. Finally, the Bibliography and Glossary have been updated.

This exploration of the ways and means of developing interior spaces begins with space itself, for it is the prime material with which the interior designer must work.

Chapter 1: Interior Space proceeds from a general discussion of architectural space to the particular characteristics of interior space in three dimensions and introduces the components of a building. The adaptive reuse of existing buildings and movement within buildings are addressed.

Chapter 2: Interior Design outlines a method for translating programmatic needs and requirements into three-dimensional design decisions. Interior architecture is introduced, as well as designing in existing buildings and historic preservation. The use of artisanal products and resiliency is addressed. Topics including design for an aging population and for children are covered, as are coworking spaces. Sustainable design rating systems and standards are updated as well. Three-dimensional printing and virtual reality are also introduced.

Chapter 3: A Design Vocabulary explores the fundamental elements and principles of visual design and applies each of them to the unique field of interior design. New information on photoreceptors in the mammalian retina and strategies for creating emphasis by using lighting and color together are presented.

Chapter 4: Interior Building Elements describes the major categories of interior elements and discusses how each affects the functional and aesthetic development of interior spaces. New options in glass wall systems and the importance of views of nature are introduced. Coverage of elevators is expanded to include machine-room-less (MRL) elevators.

Chapter 5: Interior Environmental Systems outlines the environmental control systems that must be integrated with a building's structure and the layout of the interior spaces. The role of the interior designer in educating the client about building systems is addressed. Updates in the types of plumbing fixtures are added, as is information on wireless electrical systems. Information on problems with flame retardant chemicals is also included.

Chapter 6: Lighting and Acoustics addresses the lively and ever-present interaction of light and sound with the interior environment. Recent changes in the process of lighting design and daylighting are addressed, including the increasing use of LEDs and lighting controls. Changes in the use of incandescent, fluorescent, and high-intensity discharge (HID) lamps are also covered. Current changes in the lighting industry are discussed. The integration of acoustical design into interior design practices is included, as is the importance of acoustic privacy and sound masking.

Chapter 7: Finish Materials introduces the palette used by interior designers to modify the architectural elements of interior spaces. Consideration of functional criteria is expanded to include hydrophobic properties. Finish flooring covers electrostatic discharge (ESD) issues. Coverage of bamboo flooring, terrazzo, and carpet cushions is expanded, and information on carpet recycling is updated. Coverage of composite wood panels, particleboard, medium-density fiberboard (MDF), and vacuum-formed 3D panel products and solid surfacing materials is added, and information on lead paint is expanded. Ceiling finish coverage now includes canopies and clouds.

Chapter 8: Furnishings discusses basic types of movable and built-in components within the built environment. New topics include coverage of furnishings manufactured to cross the residential/commercial barrier, and those designed to avoid undesirable materials, along with other subjects, such as Health Product Declarations (HPDs), sit-stand furniture, innovations in solar shading, and artisanal crafts.

Since interior design is to a great extent a visual art, drawings are used extensively in this book to convey information, express ideas, and outline possibilities. Some of the illustrations are quite abstract; others are more specific and particular. All of them, however, should be viewed essentially as diagrams that serve to demonstrate design principles or to clarify the relationships existing among the elements of design.

The goal of interior design education is to prepare students to be responsible, well-informed, skilled professionals who make beautiful, safe, and comfortable spaces that respect the earth and its resources. The field of interior design encompasses both visual and functional design, as well as basic knowledge of building materials, construction, and technology. This introduction to interior design is therefore broad in scope. The intent, nevertheless, is to treat the subject with clarity, make it as accessible as possible, and stimulate further in-depth study and research.

A sketch depicting the interior portion of a house.
Interior Space

Space is a prime ingredient in the designer's palette and the quintessential element in interior design. Through the volume of space we not only move; we see forms, hear sounds, feel gentle breezes and the warmth of the sun, and smell the fragrances of flowers in bloom. Space inherits the sensual and aesthetic characteristics of the elements in its field.

Space is not a material substance like stone and wood. It is inherently formless and diffuse. Universal space has no defining borders. Once an element is placed in its field, however, a visual relationship is established. As other elements are introduced into the field, multiple relationships are established between the space and the elements, as well as among the elements themselves. Space is formed by our perception of these relationships.

A sketch depicting the space present between the two persons.

The geometric elements—point, line, plane, and volume—can be arranged to articulate and define space. In architecture, these fundamental elements become linear columns and beams, planar walls, floors, and roofs.

A sketch depicting column, two columns, columns and beam, wall, floor, and roof. A zoomed view of these components is depicted in the right hand side.

In architectural design, these elements are organized to give a building form, differentiate between inside and outside, and define the boundaries of interior space.

A sketch depicting a building in space.

A building's form, scale, and spatial organization are the designer's response to a number of conditions—functional planning requirements, technical aspects of structure and construction, economic realities, and expressive qualities of image and style. In addition, the architecture of a building should address the physical context of its site and the exterior space.

A building can be related to its site in several ways. It can merge with its setting or dominate it. It can surround and capture a portion of exterior space. One of its faces can be made to address a feature of its site or define an edge of exterior space. In each case, due consideration should be given to the potential relationship between interior and exterior space, as defined by the nature of a building's exterior walls.

Buildings affect and are affected by conditions of their sites and the wider environment. Selecting and developing sites to reduce site disturbance, stormwater runoff, heat island effects, and light pollution contribute to sustainable design.

A sketch (left) depicting dominating, merging, surrounding, fronting, and defining an edge buildings. A sketch (right) depicting exterior walls.

A building's exterior walls constitute the interface between our interior and exterior environments. In defining both interior and exterior space, they determine the character of each. They may be thick and heavy, expressing a clear distinction between a controlled interior environment and the exterior space from which it is isolated. They may be thin, or even transparent, and attempt to merge inside and outside.

Windows and doorways, the openings that penetrate a building's exterior walls, are the spatial transitions between exterior and interior space. Their scale, character, and composition often tell us something about the nature of the interior spaces that lie between them.

Special transitional spaces, belonging to both the outside world and the inside, can be used to mediate between the two environments. Familiar examples include a porch, a veranda, or an arcaded gallery.

Many single-family residences have steps at all entrances that present barriers to people with physical disabilities. Visitability is a movement to construct new homes so that they can be readily lived in and visited by people with mobility impairments.

A sketch depicting thin- and thick exterior walls.
A sketch (left) depicting spatial transitions of a building. Four sketches (right) depicting different view of a house interior.
A sketch depicting the entrance of a house.

Entrances mark the transition from here to there.

Upon entering a building, we sense shelter and enclosure. This perception is due to the bounding floor, wall, and ceiling planes of interior space. These are the architectural elements that define the physical limits of rooms. They enclose space, articulate its boundaries, and separate it from adjoining interior spaces and the outside.

Floors, walls, and ceilings do more than mark off a simple quantity of space. Their form, configuration, and pattern of window and door openings also imbue the defined space with certain spatial or architectural qualities. We use terms such as grand hall, loft space, sun room, and alcove not simply to describe how large or small a space is, but also to characterize its scale and proportion, its quality of light, the nature of its enclosing surfaces, and the way it relates to adjacent spaces.

A sketch depicting the spatial qualities (form, scale, light, outlook) of a building.

Interior design necessarily goes beyond the architectural definition of space. In planning the layout, furnishing, and enrichment of a space, the interior designer should be acutely aware of its architectural character as well as its potential for modification and enhancement. The design of interior spaces requires, therefore, an understanding of how they are formed by the building systems of structure and enclosure. With this understanding, the interior designer can effectively elect to work with, continue, or even offer a counterpoint to the essential qualities of an architectural space.

A sketch depicting the interior design of a room.
The sketch depicting the layout for continuation, contrast, and counterpoint.
The sketch depicting the basic shell, modified architectually, or through interior design.
A sketch depicting the superstructure (top) and the foundation (bottom) of a building.

Buildings typically consist of physical systems of structure, enclosure, and building services equipment.

Structural Systems

These systems must work together to support the following types of loads:

Dead Loads: How a building is constructed determines its dead load, which is a static vertical load comprising the weight of its structural and nonstructural components, including any equipment permanently attached to the structure.

Live Loads: How a building is used determines its live load, which is a movable or moving load comprising the weight of its occupants and any mobile equipment and furnishings. In cold or wet climates, collected snow and water impose an additional live load on a building.

Dynamic Loads: Where a building is located determines its potential to bear a dynamic load, which can change suddenly due to the forces of wind and earthquakes.

A house's sketch depicting different types of building loads. These loads including wind load, snow load, live loads, dead loads, and earthquake are depicted in the sketch.

Enclosure System

Building Services

A sketch depicting the building envelope that consists of exterior walls, windows, doors, and roof, which protect and shelter interior spaces from the exterior environment.
A sketch outlining building services.
The sketch depicting the structural system of a building.
The sketch depicting the structural system of a building.

A building's structural system is formed according to the geometry of its materials and the way they react to the forces applied to them. This structural form and geometry, in turn, influence the dimensions, proportion, and arrangement of the interior spaces within the building volume.

The two basic linear structural elements are the column and the beam. A column is a vertical support that transmits compressive forces downward along its shaft. The thicker a column is in relation to its height, the greater its load-bearing capacity and its ability to resist buckling resulting from off-center loading or lateral forces.

A beam is a horizontal member that transmits forces perpendicular to itself along its length to its supports. A beam is subject to bending and deflection, which result in an internal combination of compressive and tensile stresses. These stresses are proportionally greater along the upper and lower region of a beam's cross section. Increasing depth and placing material where stresses are greatest optimize a beam's performance.

Figure depicting the effects of compression and tension on beams. The length and breadth of the beam are represented by L and D, respectively.

Beams are subject to bending.

Figure depicting the effects of compression and tension on beams. The length and breadth of the beam are represented by L and D, respectively.

Increasing a beam's depth enables it to span greater distances.

Columns mark points in space and provide a measure for its horizontal divisions. Beams make structural and visual connections across space between their supports. Together, columns and beams form a skeletal framework around interconnected volumes of space.

A linear structural system may suggest a grid layout of repetitive spaces, but floor, wall, and ceiling planes are necessary for the support and enclosure of interior space. Floor and ceiling planes, which define the vertical limits of space, may consist of planar slabs or a hierarchical arrangement of girders (large primary beams) and beams and joists (a series of smaller, parallel beams). Walls and partitions need not be load-bearing and do not have to be aligned with the columns of a structural frame, except where serving as shear walls and providing for lateral stability. They are free to define the horizontal dimensions of space according to need, desire, or circumstance.

Linear structural systems are cumulative by nature and eminently flexible. They allow for growth, change, and the adaptation of individual spaces to their specific uses.

A sketch of a building depicting the development of space by addition and defining space by subtraction.
A sketch of a building depicting non-load-bearing partitions and structural grid.

Small beams or lintels are required to span openings in bearing walls.

Varying degrees of spatial enclosure are possible with walls, depending on the size and location of openings within their planes.

The two principal types of planar structural elements are the load-bearing wall and the horizontal slab. A bearing wall acts as a long, thin column in transmitting compressive forces to its support or foundation.

Window and door openings within a bearing wall tend to weaken its structural integrity. Any opening must be spanned by an arch or a short beam called a lintel to support the wall load above and allow compressive stresses to flow around the opening to adjacent sections of the wall.

A common pattern for bearing walls is a parallel layout spanned by floor joists and roof rafters, or by horizontal slabs. For lateral stability, pilasters and cross walls are often used to help brace bearing walls.

Figure depicting pilasters and cross walls used to help brace bearing walls.

While linear structural elements outline the edges of spatial volumes, planar elements such as bearing walls define the physical limits of space. They provide a real sense of enclosure and privacy as well as serve as barriers against the elements.

A slab is a horizontal, rigid, usually monolithic plate. A common example is a reinforced concrete slab. A slab is able to support both concentrated and distributed loads because the resulting stresses can fan out across the plane of the slab and take various paths to the slab supports.

When supported along two edges, a slab can be considered a wide, shallow beam extending in one direction. Supported along four sides, a slab becomes a two-way structural element. For greater efficiency and reduced weight, a slab can be modified in sections to incorporate ribs.

When integrally connected with reinforced concrete columns, flat slabs can be supported without beams. They form horizontal layers of space punctuated only by the shafts of the supporting columns.

Figure depicting a sketch of a building where slabs are supported by a framework of beams and columns or by a masonry or concrete bearing wall.

Slabs may be supported by a framework of beams and columns or by a masonry or concrete bearing wall.

A building sketch depicting two-way flat slabs thickened at their column supports define horizontal layers of space.

Two-way flat slabs thickened at their column supports define horizontal layers of space.

Figure depicting four types of slabs.
The sketch depicting a volumetric structural system that consists of a three-dimensional mass.

Composite systems combine linear, planar, and volumetric elements into three-dimensional compositions of form and space.

A volumetric structural system consists of a three-dimensional mass. The mass of the material occupies the void of space. The volume of interior space is carved out of the mass. The efficiency of engineering methods and the strength of modern building materials have limited the use of pure volumetric structural systems, although three-dimensional computer design is changing this; an example is the Walt Disney Concert Hall designed by Frank Gehry. At a small scale, stone and clay masonry units can be seen to be volumetric structural elements. At a larger scale, any building that encloses interior space can be viewed as a three-dimensional structure that must have strength in width, length, and depth.

A sketch depicting Walt Disney Concert Hall, Los Angeles, California, Frank Gehry, 2003.

Walt Disney Concert Hall, Los Angeles, California, Frank Gehry, 2003

Most structural systems are in fact composites of linear, planar, and volumetric elements. No one system is superior to all others in all situations. For the structural designer, each presents advantages and disadvantages, depending on the size, location, and intended use of a building. An interior designer should be aware of the character of the interior spaces each system defines.

An interior design depicting partitions, ceilings, and furniture.

Although a building's structural system sets up the basic form and pattern of its interior spaces, these spaces are ultimately structured by the elements of interior design. The term “structure” is not used here in the sense of physical support. It refers to the selection and arrangement of interior elements such that their visual relationships define and organize the interior space of a room.

Non-load-bearing partitions and suspended ceilings are often used to define or modify space within the structural framework or shell of a building.

The color, texture, and pattern of wall, floor, and ceiling surfaces affect our perception of their relative positions in space and our awareness of the room's dimensions, scale, and proportion.

Figure (left) depicting furniture grouping and a dominant element. Figure (right) depicting artificial lightning and daylighting.

Within a large space, the form and arrangement of furnishings can divide areas, provide a sense of enclosure, and define spatial patterns.

Lighting, and the light and dark patterns it creates, can call our attention to one area of a room, deemphasize others, and thereby create divisions of space.

Even the acoustic nature of a room's surfaces can affect the apparent boundaries of a space. Soft, absorbent surfaces muffle sounds and can diminish our awareness of the physical dimensions of a room. Hard surfaces that reflect sounds within a room help to define its physical boundaries. Echoes can suggest a large volume.

Finally, space is structured by the way we use it. The nature of our activities and the rituals we develop in performing them influence how we plan, arrange, and organize interior space.

An interior sketch depicting color, texture, and pattern.

Color, texture, and pattern

An interior sketch (left) depicting communication and movement. An interior sketch (right) depicting individual and group activities.

Interior spaces are formed first by a building's structural system, further defined by wall and ceiling planes, and related to other spaces by windows and doorways. Every building has a recognizable pattern of these elements and systems. Each pattern has an inherent geometry that molds or carves out a volume of space into its likeness.

It is useful to be able to read this figure–ground relationship between the form of space-defining elements and that of the space defined. Either the structure or the space can dominate this relationship. Whichever appears to dominate, we should be able to perceive the other as an equal partner in the relationship.

It is equally useful to see the alternating figure–ground dominance occurring as interior design elements, such as tables and chairs, are introduced and arranged within an interior space.

When a chair is placed in a room, it not only occupies space, it also creates a spatial relationship between itself and the surrounding enclosure. We should see more than the form of the chair. We should also recognize the form of the space surrounding the chair after it has filled some of the void.

As more elements are introduced into the pattern, the spatial relationships multiply. The elements begin to organize into sets or groups, each of which not only occupies space but also defines and articulates the spatial form.

The dimensions of interior space, like spatial form, are directly related to the nature of a building's structural system—the strength of its materials and the size and spacing of its members. The dimensions of a space, in turn, determine a room's proportion and scale and influence the way it is used.

One horizontal dimension of space, its width, has traditionally been limited by the materials and techniques used to span it. Today, given the necessary economic resources, almost any architectural structure is technically possible. Wood or steel beams and concrete slabs can span up to 30 feet (9 m). Wood or steel trusses can span even farther, up to 100 feet (30 m) or more. Longer roof spans are possible with space frames and a variety of curved structures, such as domes, suspension systems, and membranes supported by air pressure.

Within the bounds of structural necessity, the width of an interior space should be established by the requirements of those who use the space and their need to set boundaries for themselves and their activities.

Building designers have traditionally developed spatial relationships by sketching and model building. Computer-aided design (CAD) and building information management (BIM) software systems are changing the way that building designers work. These computer technologies allow designers to build interactive three-dimensional computer models of buildings, and to coordinate building systems as they design.

Modeling a building with a 3D CAD system can provide higher productivity, rapid generation of design alternatives, and removal of errors that result from disparities between different drawings. However, these systems do require special design and management skills.

The other horizontal dimension of space, its length, is limited by desire and circumstance. Together with width, the length of a space determines the proportion of a room's plan shape.

A square room, where the length of the space equals its width, is static in quality and often formal in character. The equality of the four sides focuses our attention in on the room's center. This centrality can be enhanced or emphasized by covering the space with a pyramidal or dome structure.

To deemphasize the centrality of a square room, the form of the ceiling can be made asymmetrical, or one or more of the wall planes can be treated differently from the others.

Figure depicting a pyramidal or dome structure.

Pyramids, domes, and similar roof forms can emphasize the centrality of square spaces.

Figure depicting the centrality of a square room, the form of the ceiling made asymmetrical, or one or more of the wall planes treated differently from the others.
Figure (top) depicting pyramids, domes, and similar roof forms that emphasize the centrality of square spaces. Figure (bottom) depicting the placement of architectural elements, such as windows and stairways, are deemphasize the centrality of square spaces.

The placement of architectural elements, such as windows and stairways, can deemphasize the centrality of square spaces.

Horizontal dimensions alone do not determine the ultimate qualities and usefulness of a space. They only suggest opportunities for development.

Square rooms are rare and distinctive. More often, a room will have a length greater than its width. A rectangular space, normally spanned across its width, is eminently flexible. Its character and usefulness are determined not only by its proportion of width to length, but also by the configuration of its ceiling, the pattern of its windows and doorways, and its relationship to adjacent spaces.

When the length of a space is greater than twice its width, it tends to dominate and control the room's layout and use. Given sufficient width, the space can be divided into a number of separate but related areas.

A space whose length greatly exceeds its width encourages movement along its long dimension. This characteristic of linear spaces makes them suitable for use as gallery spaces or as connectors of other spaces.

Linear spaces may be subdivided with furnishings or by architectural elements.

Both square and rectangular spaces can be altered by addition or subtraction, or by merging with adjacent spaces. These modifications can be used to create an alcove space or to reflect an adjoining element or site feature.

Figure depicting the curvature of a wall.

The radius of the curvature of a wall depends on the scale and flexibility of the material used to build it.

The nature of building materials and the techniques used to assemble them have traditionally established rectangular spaces as the norm. Curvilinear spaces are exceptional and usually reserved for special circumstances. However, the advent of 3D CAD systems has made the design and construction of curvilinear spaces more feasible.

The simplest curvilinear space is a circular one. It is compact and self-centering. Although it creates a focus on its center, a circular space also relates to the surrounding space equally in all directions. It has no front, back, or sides, unless these are defined by other elements.

An elliptical space is more dynamic, having two centers and unequal axes.

Other curvilinear spaces can be seen as transformations of circular or elliptical spaces that have been combined in an overlapping manner. The use of three-dimensional computer modeling is increasing the ease of designing complex curves.

Within a rectilinear context, a curvilinear space is highly visible. Its contrasting geometry can be used to express the importance or uniqueness of its function. It can define a freestanding volume within a larger space. It can serve as a central space about which other rooms are gathered. It can articulate the edge of a space and reflect an exterior condition of the building site.

Curved walls are dynamic and visually active, leading our eyes along their curvature. The concave aspect of a curved wall encloses and focuses space inward, while its convex aspect pushes space outward.

An important consideration when we are dealing with a curvilinear space is the integration of furniture and other interior elements into its volume. One way of resolving conflicting geometries is to arrange interior forms as freestanding objects within the curvilinear space. Another is to integrate the form of built-in furniture and fixtures with the curved boundaries of the space.

Figure depicting the walls curving to respond to an exterior condition. On the left, the circular space is situated as a freestanding object. On the right, circular space is serving as an organizing element.

Walls curving to respond to an exterior condition

Figure (left) depicting curved walls that are dynamic and visually active, leading our eyes along their curvature. The concave aspect of a curved wall encloses and focuses space inward, while its convex aspect pushes space outward. Figure (right) depicting the furnishings placed as freestanding objects within a curvilinear space or be integrated within the curved forms.

Furnishings may be placed as freestanding objects within a curvilinear space or be integrated within the curved forms.

The third dimension of interior space, its height, is established by the ceiling plane. This vertical dimension is as influential as the horizontal dimensions of a space in forming the spatial quality of a room. Design of the ceiling is an important element of interior design.

While our perception of a room's horizontal dimensions is often distorted by the foreshortening of perspective, we can more accurately sense the relationship between the height of a space and our own body height. A measurable change in the height of a ceiling seems to have a greater effect on our impression of a space than a similar change in its width or length.

Varying the ceiling height can have a powerful effect on the perceived scale of a space.

High ceilings are often associated with feelings of loftiness or grandeur. Low ceilings may connote cavelike coziness and intimacy. However, our perception of the scale of a space is affected not by the height of the ceiling alone, but by its relationship to the width and length of the space as well.

A ceiling defined by the floor plane of the room above it is typically flat. A ceiling created by a roof structure can reflect its form and the manner in which it spans the space. Shed, gable, and vaulted ceiling forms give direction to space, while domed and pyramidal ceilings emphasize the center of a space.

Lowering part of a ceiling can foster intimacy, modify acoustics, or add visual texture. Interior soffits, canopies, and clouds can be used to partially lower a ceiling at its perimeter, or over areas of interest.

Figure depicting the roof structure of a building.

The roof structure can sometimes be left exposed, giving texture, pattern, and depth to the ceiling plane.

Figure (top) depicting the structure of shed, gable, and vaulted ceilings. Figure (bottom) depicting the pyramids and domes that emphasize the centrality of a space.

Although individual spaces may be designed and formed for a certain purpose or to house certain activities, they are gathered together within a building's enclosure because they are functionally related to one another, are used by a common group of people, or share a common purpose. How interior spaces are related to one another is determined not only by their relative position in a building's spatial pattern, but also by the nature of the spaces that connect them and the boundaries they have in common.

Floor, wall, and ceiling planes serve to define and isolate a portion of space. Of these, the wall plane, being perpendicular to our normal line of sight, has the greatest effect as a spatial boundary. It limits our visual field and serves as a barrier to our movement. Openings created within the wall plane for windows and doorways reestablish contact with the surrounding spaces from which the room was originally cut.

Doorways provide physical access from one space to another. When closed, they shut a room off from adjacent spaces. When open, they establish visual, spatial, and acoustical links between spaces. Large open doorways erode the integrity of a room's enclosure and strengthen its connection with adjacent spaces or the outdoors.

The thickness of the wall separating two spaces is exposed at a doorway. This depth determines the degree of separation we sense as we pass through the doorway from one space to another. The scale and treatment of the doorway itself can also provide visual clues to the nature of the space being entered.

The number and location of doorways along a room's perimeter affect our pattern of movement within the space, and the ways we may arrange its furnishings and organize our activities.

The widths of door openings affect the ease of movement for people and furnishings. A 36-inch (914-mm) wide doorway is reduced to about 32 inches (813 mm) when the thickness of the open door and that of its hardware are taken into consideration. Clear openings of less than 32 inches (813 mm) become barriers to standard wheelchairs, affecting accessibility, visitability, and aging-in-place.

Figure (top) depicting the doors fitted in the rooms. The sketch (bottom) depicting the model of a room where doors are indicated by arrows.

Doorway locations affect our patterns of movement and activities within a room.

Figure depicting the open door of a room.

Windows let light and air into the interior spaces of buildings and provide views of the outdoors, or from one space to another. Their size and placement, relative to the wall plane in which they occur, also affect the degree of separation between an interior space and the exterior environment. Views to the outside and natural ventilation are important elements in sustainable design.

Windows framed within a wall plane attract our attention with their brightness and outlook but maintain the enclosure provided by the wall. Large windows and glass walls attempt, at least visually, to merge indoor and outdoor space. The visual treatment of the window frames in each case can either emphasize or minimize the perceived limits of interior space.

Interior windows can, in a similar manner, visually expand a room beyond its physical boundaries and allow it to become an integral part of the surrounding interior space.

Stairways are also important forms of spatial transitions between rooms. An exterior set of steps leading to a building's entrance can serve to separate private domain from public passage and enhance the act of entry into a transitional space such as a porch or terrace. Entrances without steps support visitability and aging-in-place.

Interior stairways connect the various levels of a building. The manner in which they perform this function shapes our movement in space—how we approach a stairway, the pace and style of our ascent and descent, and what we have an opportunity to do along the way. Wide, shallow steps can serve as an invitation, while a narrow, steep stairway may lead to more private places. Landings that interrupt a flight of steps can allow a stairway to change direction and give us room for pause, rest, and outlook.

Designers are becoming more concerned with creating opportunities for movement within interior workplace spaces. One result of this has been the increasing use of wide stairs as seating areas, often connecting work or presentation spaces.

Active design focuses on the role of designers in dealing with the urgent health crises of obesity and related diseases such as diabetes. Active design guidelines go beyond Leadership in Energy and Environmental Design (LEED) programs to address people's varying needs and educate designers about opportunities to increase daily physical activity and include measures such as making stairs more visible and inviting. They seek to increase stair use by providing a conveniently located stair for everyday use, posting motivational signage to encourage stair use, and designing visible, appealing, and comfortable stairs.

The space a stairway occupies can be considerable, but its form can be fit into an interior in several ways. It can fill and provide a focus for a space, run along one of its edges, or wrap around a room. It can be woven into the boundaries of a space or be extended into a series of terraces.

The sketch depicting the reconfiguration of an existing space that requires removal of walls and construction of new ones.
The sketch depicting the addition of new space in the house.

The architectural planning and design for a new building take into account the nature of the activities to be housed; the spatial requirements for form, scale, and light; and the desired relationships among the various interior spaces. When an existing building is to be used for activities other than those for which it was originally intended, however, activity requirements must be matched with the existing conditions. Where a misfit occurs, a modification of the existing spaces may be required.

Today, many interior renovations involve changes to existing buildings. Where the design involves changes in the building's use, the process is referred to as adaptive reuse. Reusing existing buildings can help preserve the historic qualities and architectural character of a built environment.

Two major types of alteration can be considered. The first involves structural changes in the boundaries of interior space and is more permanent in nature than the second. The second type of alteration involves nonstructural modifications and enhancement accomplished through interior design.

The acceptance of formerly forbidden accessory dwelling units (ADUs) offer opportunities to create residential units in existing owner-occupied one- to three-family buildings in certain neighborhoods. The ADUs create an opportunity to evolve older residences to meet 21st-century housing needs, while promoting long-term occupancy and neighborhood stability.

A structural change may involve removing or adding walls to alter the shape and rearrange the pattern of existing spaces, or to add on new space. When making such alterations, it is extremely important to understand the distinction between load-bearing walls and non-load-bearing partitions. It is, therefore, always advisable to consult a professional engineer or architect when making structural changes to a space.

Within the boundaries of a space, the existing pattern of openings can also be altered. Windows may be enlarged or added for better daylighting or to take advantage of a view. A doorway may be moved or added for better access to a room space or to improve the movement paths within the space. A large doorway may be created to merge two adjacent spaces. Any new or enlarged opening in a load-bearing wall requires a lintel or header sized to carry the wall load above the opening.

To add a stairway, daylight a space with skylights, or create a vertical relationship between two levels of space, structural changes in the floor or ceiling plane may be required. Alterations in these horizontal structures of a building may require that the edges of any new openings be reinforced and supported by a system of beams, columns, posts, or bearing walls.

Sketch depicting the structural support required along edges of new floor and roof openings.

Structural support is required along edges of new floor and roof openings.

Sketch depicting new wall opening, space is extended outward (top) and an existing opening is enlarged (bottom).
Sketch depicting new wall opening, space is extended outward (top) and an existing opening is enlarged (bottom).
Sketch depicting the vertical expansion in the room.

Even as we deal with specific design issues and with different aspects of a building's interior spaces, we should be mindful of the overall structure and patterns of the architecture. In particular, any changes in the physical boundaries of a space must be carefully planned so that the structural integrity of a building is not disturbed. Major structural changes in a space, therefore, require the assistance of a professional engineer or architect.

Interior spaces can be modified and enhanced with nonstructural alterations, however. While structural changes alter the physical boundaries of space, nonstructural alterations are based on how we perceive, use, and inhabit space. These are the types of changes commonly planned and executed by interior designers.