The interior design guide
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The interior design guide. A definitive knowledge base for interior designers.

From first principles to the finishing touches: shell, surfaces, space planning, furniture, electrics, plumbing and joinery, in the order a project runs.

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The Lexicon.

Every term, in plain words.

From hue and light reflectance to bonding and kick space, every term the guide uses has a short definition, what to know in practice and the pages that use it.

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The interior design guide.

A definitive knowledge base for interior designers.

Eleven chapters take a home from first principles to the moment you show it to the client. Start with Foundations and read in order, or search for a topic, a term or a rule of thumb.

Chapters.

Eleven steps, from principles to presentation.

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Where to go next.

Sections.

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Where to go next.

Codes and rules,

finding and following the requirements that apply.

Every interior answers to rules that protect the people who use it. This page shows how to find which ones apply, design to them, and carry them through to completion.

Rules and scope.

Establish which requirements apply before designing.

Start by telling apart three kinds of document. Regulations are law: building codes and the rules that enforce them. Technical standards describe how to test, size or build something, and become mandatory when a regulation cites them. Guidance explains one accepted way to comply. Then pin down the project: where it is, what the building is used for, how many people will be in it and what work is proposed. These decide which codes apply, which editions and which local amendments. In a renovation, investigate what is already there, including the structure, the services, any protected features and possible hazardous materials such as asbestos. Alterations, and above all a change of use, can trigger requirements that the existing building never had to meet.

Office
Restaurant
The same tenancy as an office, then as a restaurant. The new use brings new checks and changes others.

Work through these steps before drawing anything. They establish which rules apply, which editions and amendments are in force, and what the existing building and the proposed changes will demand. Record the answers as you go: they become the reference every later decision is checked against.

  1. 01LocateIdentify the jurisdiction and the authorities responsible for approvals.
  2. 02ClassifyRecord the existing and proposed use, the occupant capacity and the scope of work.
  3. 03SurveyIdentify existing constraints and the specialist investigations needed.
  4. 04Check triggersInvestigate the requirements that the proposed changes bring with them.
  5. 05RecordList the applicable sources and editions, and the questions still open.

Safety.

Prevent everyday injuries and enable safe escape.

Safety covers two situations. In an emergency, people must reach a place of safety: escape routes, exits, travel distances and widths, and the fire and smoke separation that protects them, including doors, finishes and the services that pass through fire-resisting walls. Every day, people must move around without harm: stairs and changes in level, guarding at drops, glazing people might walk into, slippery floors and collision risks. Furniture changes the usable width of a route, so test layouts with chairs pulled out and doors open. A product is only as good as its application: a fire-rated door or a slip-resistant tile performs as tested only within the complete assembly it was tested in. See circulation and clearance.

Everyday use
Emergency
Furniture moved
One floor read for everyday hazards, then for escape, then with a cabinet pushed into the route.

Review each layout with these checks, on the plan and again with the furniture in place, doors open and chairs pulled out. Repeat them whenever the layout changes: a moved partition or a new piece of storage can narrow a route or block an exit.

  1. 01Trace escapeCheck routes, travel distances, widths and exits against the applicable requirements.
  2. 02Test movementAccount for furniture in use, door swings and changes in level.
  3. 03Review hazardsCheck stairs, guarding, glazing and floor surfaces.
  4. 04Check separationCoordinate fire-resisting walls, doors and service penetrations.
  5. 05Verify specificationsConfirm the required performance of finishes and assemblies.

Accessibility.

Enable people with different disabilities to use the space.

Treat accessibility as a continuous journey: arriving, entering, moving around, using the facilities, receiving information and leaving safely, including in an emergency. Design for mobility, visual, hearing and cognitive needs, not only for wheelchair users: clear floor space alone does not make a space accessible. Identify the obligations that apply. In the United States these are the ADA Standards for Accessible Design, issued under the Americans with Disabilities Act, together with state and local codes, which can be stricter. Elsewhere the equivalents are national and local provisions, such as Part M of the Building Regulations in England, the Equality Act 2010 in the United Kingdom, or EN 17210 in Europe. Then decide, with the client, where the design should go beyond the legal minimum: inclusive design serves far more people than any rule requires.

Entrance
Reception
Workstation
Toilet
One journey through an office: at each stop, a different requirement comes into play.

Walk the plan as a disabled visitor would, from the street to every space they need and back out in an emergency. Test each step for people with mobility, visual, hearing and cognitive needs, not only for wheelchair users.

  1. 01IdentifyEstablish which accessibility rules apply to the project and to the alterations.
  2. 02ConnectTrace an accessible route to the spaces and amenities people need.
  3. 03Test operationCheck doors, manoeuvring space, controls, seating and work surfaces.
  4. 04Check facilitiesReview toilets, washing areas and other amenities against the relevant requirements.
  5. 05CommunicateConsider readable signage, contrast, lighting, and audible and visual information.
  6. 06Review evacuationCoordinate provisions for occupants who may need assistance to leave.

Comfort and services.

Provide healthy indoor conditions and coordinate essential systems.

Codes also set the conditions people live and work in: ventilation, lighting, acoustics, thermal comfort and, increasingly, energy use. The guide covers each in its own page: Light, Acoustics and Temperature. In wet areas, add drainage, waterproofing and protection against scalding from hot water. Interiors and services meet everywhere: partitions change how air moves, ceilings carry lights, detectors and sprinklers, and joinery can hide the equipment that needs servicing. Bring in specialists early, compare the layouts drawn by each of them, and keep every control, valve and access panel reachable: an attractive layout must also let the building work.

Conditions
Services
Conflicts
A room with its ceiling void open: light and air, then the services, then the conflicts a new partition and a cupboard create.

Coordinate the interior with the services before the design is fixed, when changes are still cheap. Lay each specialist's drawings over your own, look for clashes between partitions, ceilings, joinery and equipment, and keep every point that needs maintenance within reach.

  1. 01Review conditionsIdentify the applicable indoor-environment and energy requirements.
  2. 02Check layoutsConsider how room depth, partitions and occupancy affect light, air and sound.
  3. 03Resolve wet areasCoordinate fixtures, drainage and moisture protection.
  4. 04Overlay servicesCompare the ceiling, lighting, electrical, ventilation and fire-safety layouts.
  5. 05Preserve accessKeep equipment, controls and maintenance points accessible.

Checks and approvals.

Carry requirements from design decisions through to completion.

Keep a simple record of each requirement: where it comes from and how the design responds. Building-control approval, which checks compliance with the building regulations, is separate from planning permission, which controls use and appearance, and from other permissions such as landlord, heritage or licensing consents. Agree who prepares, coordinates and checks each requirement, who submits what and when, and who attends which inspections. Collect evidence for products and assemblies, and recheck every substitution and site change: an equivalent product is not equivalent until its evidence says so. At the end, keep the completion records and the operating information, so the finished interior can be used and maintained as intended.

Plan
Specification
Installation
Completion
Substitution
One fire-resisting door, from the plan to its completion evidence. A substitute leaf resets every check.

Carry each requirement from the first drawings through to the finished interior. Make sure every decision has an owner, every product has its evidence, and every change on site is checked again before it is built.

  1. 01AssignIdentify who prepares, coordinates and checks each requirement.
  2. 02DocumentLink each requirement to drawings, details and specifications.
  3. 03SubmitEstablish the permissions required and their timing.
  4. 04Recheck changesReview substitutions and site changes before they are carried out.
  5. 05Close outCollect inspection records, certificates, as-built information and operating instructions.

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Where to go next.

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2 · Running a project

Questions.

What people ask most about codes and rules.

What is a certificate of occupancy?

It is the document the local building department issues to confirm that a building, or a space within it, complies with the codes and can be occupied for its intended use. It is usually needed after new construction, after a major renovation and whenever the use changes, for example when an office becomes a restaurant. Without it, a tenant may not be allowed to open.

What is a building permit, and does an interior project need one?

A building permit is permission from the local building department to carry out specific work, followed by inspections. Interior projects usually need one when they move or remove walls, alter the structure, change the layout of rooms or exits, or add or alter electrical, plumbing, gas or ventilation work. Painting, new flooring and like-for-like cabinet replacements often do not. The rules vary by place, so check with the local department before the design is fixed.

What does ADA compliant mean?

It means a space meets the 2010 ADA Standards for Accessible Design, the technical rules under the Americans with Disabilities Act. They apply to public accommodations, commercial facilities and state and local government buildings in the United States, including shops, restaurants, offices and hotels. Private homes are generally not covered, although state and local codes may add their own requirements.

What are the requirements for an ADA-compliant bathroom?

Under the 2010 ADA Standards, a single-user toilet room needs a 60 inch turning circle or a T-shaped turning space, a door with at least 32 inches of clear width, a toilet centred 16 to 18 inches from the side wall, grab bars on the side and rear walls mounted 33 to 36 inches above the floor, a sink no higher than 34 inches with knee space below, and a mirror whose reflecting surface starts no higher than 40 inches. Controls must work with one hand, without tight grasping or twisting.

What is the maximum slope of an ADA ramp?

The 2010 ADA Standards allow a running slope of no more than 1:12, which is one inch of rise for every 12 inches of run. Each run may rise at most 30 inches before a level landing, the cross slope may not exceed 1:48, and a ramp that rises more than 6 inches needs handrails on both sides. A gentler slope is easier for everyone.

What is the ADA counter height?

Sales and service counters need a section at least 36 inches long and no higher than 36 inches above the floor, so a wheelchair user can approach and be served. Work surfaces and dining surfaces for public use should be 28 to 34 inches high, with knee clearance below.

What is the minimum ADA door width?

A door must give at least 32 inches of clear width, measured with the door open at 90 degrees between the face of the door and the opposite stop. Thresholds may be no higher than half an inch, bevelled, and the door needs clear manoeuvring space on both sides and hardware that works without tight grasping.

What is an egress window?

An egress window is a window large enough for people to escape through and for firefighters to enter. In the United States, the International Residential Code requires one in every sleeping room and in habitable basements, with a net clear opening of at least 5.7 square feet, at least 24 inches high and 20 inches wide, and a sill no more than 44 inches above the floor. A basement bedroom without one cannot legally be called a bedroom.

What is the standard height of a handrail?

Both the International Residential Code and the International Building Code set stair handrails at 34 to 38 inches above the stair nosings. In England, Approved Document K sets 900 to 1000 mm. Handrails must be continuous and easy to grip, and accessible routes often need one on each side.

What is the building code for stairs?

Under the International Residential Code, a stair in a home may have risers of at most 7¾ inches and treads of at least 10 inches, with at least 6 feet 8 inches of headroom. The International Building Code is stricter for other buildings: risers of 4 to 7 inches and treads of at least 11 inches. Keep every riser and tread in a flight the same size: uneven steps cause falls.

What is a fire-rated door?

A fire-rated door is a complete door assembly, including the leaf, frame, hinges, closer, seals and any glazing, that has been tested to hold back fire for a set time, such as 20, 60 or 90 minutes. It carries a label, must close and latch on its own, and only performs as tested when installed as tested. Changing any part, from the hinges to a vision panel, can void the rating.

Units