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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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.

Keep reading.

Where to go next.

Lexicon.

The shared vocabulary.

Every page links here on a concept's first use. Each entry gives a short, plain definition.

Foundations 30

Hue

Hue is a colour’s family: red, yellow, blue-green and so on, its position on the colour wheel. It is what most people mean by “colour”, and usually the least important of the three dimensions in a room.

Value

Value is how light or dark a colour is, independent of its hue. A pale blue and a pale pink can share the same value.

Saturation

Saturation (or chroma) is a colour’s intensity: how far it is from grey. High saturation is vivid; low saturation is muted, dusty or greyed.

Complementary colours

Complementary colours sit opposite each other on the colour wheel, such as blue and orange or red and green. Placed together they intensify each other; mixed, they neutralise to grey.

Analogous colours

Analogous colours sit next to each other on the colour wheel, such as yellow-green, green and blue-green. They share a common hue, so they harmonise easily.

60-30-10 rule

The 60-30-10 rule is a rule of thumb for colour proportion: about 60% dominant colour, 30% secondary and 10% accent. It describes how much of each colour a room shows, not how many colours it has.

Anthropometrics

Anthropometrics is the measurement of the human body: heights, reaches, widths and how they vary between people. It is the data behind every seat height, worktop and doorway.

Proxemics

Proxemics is the study of how people use distance between one another, described by the anthropologist Edward T. Hall. He named four zones: intimate (to 45 cm), personal (45–120 cm), social (1.2–3.6 m) and public (beyond).

Plan

A plan is a horizontal section through a building, cut about 1.2 m above the floor and viewed from above. Cut walls are drawn heaviest or filled; everything below the cut is drawn lighter.

Section

A section is a vertical cut through a building or room, taken along a line marked on the plan. It shows heights and levels: ceilings, floors, sills, steps and the spaces between them.

Elevation

An elevation is a straight-on, flat view of one face of a wall or building, with nothing cut. It shows what sits on the surface and at what height.

Axonometric

An axonometric is a three-dimensional drawing in which parallel lines stay parallel, unlike a perspective. Lengths along each of its three axes can be measured.

Scale

Scale is how big an object is relative to the room it sits in and to the human body. A piece can be well proportioned in itself and still be out of scale for its room.

Proportion

Proportion is the size relationship between the parts of a thing, and between the parts and the whole. It is why a cabinet on slim legs reads elegant and the same cabinet on stubby legs reads clumsy.

Visual weight

Visual weight is how heavy an object looks, whatever it actually weighs. Darkness, size, solidity, saturation and texture add weight; light colours, legs and open frames take it away.

Hierarchy

Hierarchy is the order in which the eye reads a room. Good rooms have one dominant element, a few secondary ones, and everything else in support.

Focal point

A focal point is the element the eye lands on first when you enter a room. It can be architectural (a fireplace, a view) or created (art, a coloured wall, a striking piece).

Rhythm

Rhythm is the repetition of a shape, colour, material or interval that carries the eye through a space. It turns separate objects into one composition.

Contrast

Contrast is the difference in tone, texture, scale or form between elements. Too little and a room reads flat; too much and it reads restless.

Negative space

Negative space is the empty area around and between objects. It gives important pieces room to read and gives the eye somewhere to rest.

Prospect and refuge

Prospect and refuge is a theory from landscape psychology (Jay Appleton): people prefer spots where they can see out while protected behind. It explains why the corner banquette fills first and the chair with its back to the door stays empty.

Reverberation

Reverberation is how long sound lingers in a room after its source stops. Hard, parallel surfaces lengthen it; soft, porous and irregular ones shorten it.

Airborne sound

Airborne sound travels through the air: voices, music, a television. It reaches the next room through walls, doors and any gap.

Impact sound

Impact sound starts when something strikes the structure, such as footsteps, a dropped object or a slammed door, and travels through floors and walls.

Noise reduction coefficient

The noise reduction coefficient (NRC) is a single number for how much sound a material absorbs across the speech range, from 0 (all reflected) to 1 (all absorbed).

Flanking path

A flanking path is a route sound takes around a wall rather than through it: through a shared floor, ceiling, duct or joint.

Mean radiant temperature

Mean radiant temperature is the average temperature of all the surfaces around a person, weighted by how much of their view each one takes up.

Operative temperature

Operative temperature combines the air temperature with the mean radiant temperature into one number closer to what a person feels.

Thermal mass

Thermal mass is a material’s ability to store heat and release it later. Stone, concrete, brick and tile have a lot; timber and plasterboard have little.

Solar gain

Solar gain is the heat a room receives from the sun through its windows.

Running a project 7

Brief

A brief is the client’s statement of what the project must achieve: who it is for, what it must include, the budget, the timescale and any fixed constraints.

Program

A program, or space schedule, turns the brief into spatial requirements: each activity, its users, its target area and the spaces it must sit near.

Concept

A concept is the central idea a design is built on: a layout strategy, a mood and a material direction that answer the brief together.

Design development

Design development is the stage that turns an approved concept into a resolved design: fixed layouts, chosen finishes, sized joinery and coordinated services.

Tender

A tender is the process of asking contractors to price the same set of documents, so their prices can be compared like for like.

Specification

A specification is the written description of what is to be supplied and how it is to be installed: products, materials, finishes, standards and workmanship.

Snagging

Snagging is the inspection near the end of a project that lists defects and unfinished work, called snags, for the contractor to put right before handover.

Surfaces 7

Undertone

An undertone is the underlying hue inside a colour, such as the green in a grey or the pink in a beige. It hides on its own and shows up next to other colours or as the light changes.

LRV

LRV (light reflectance value) is the share of visible light a colour reflects, from 0 for black to about 100 for pure white. Most paint makers print it on the chip.

Metamerism

Metamerism is when two colours match under one light and differ under another. It happens because the materials reflect different mixes of wavelengths.

Sheen

Sheen is how much light a finish reflects, from flat matt through eggshell and satin to gloss. Higher sheen is tougher and easier to wipe, but shows every flaw in the surface.

Colour drenching

Colour drenching is painting walls, trim, doors and often the ceiling in one colour. Edges and junctions disappear, so the room reads as one volume.

Junction

A junction is where two materials or planes meet: floor to wall, wall to ceiling, tile to timber. It is where workmanship shows, and where most perceived quality is decided.

Shadow gap

A shadow gap is a small recessed reveal, often around 10 mm, left between two planes instead of a direct joint. It reads as a crisp dark line and hides small imperfections.

Space planning 7

Circulation

Circulation is the set of routes people walk through a room or a home. Good circulation is direct, clear of furniture, and never cuts through a conversation area.

Clearance

Clearance is the minimum free space needed to use or pass a piece of furniture or a fixture. It is set by the body: knees, a chair pushed back, a door or drawer swung open.

Sightline

A sightline is the line of view from a key point, such as the front door or the sofa, to what sits at the end of it. Designers use sightlines to frame what should be seen and hide what shouldn’t.

Zoning

Zoning divides an open space into areas by use, such as cooking, eating and sitting, without building walls. Rugs, light, ceiling changes, furniture backs and changes of floor mark the zones.

Adjacency

Adjacency is which spaces need to sit next to each other, and which must be kept apart. Kitchen next to dining, bathroom near bedrooms, front door away from the sofa’s back.

Bubble diagram

A bubble diagram is a quick sketch of a plan’s zones as loose circles, sized roughly by area and linked by how people move between them. It fixes relationships before shapes.

Test fit

A test fit is placing real furniture at real size into a plan to prove the layout works. It catches what a room schedule hides: doors that hit sofas, beds with no way round.

Furnishing 4

Anchor piece

The anchor piece is the largest or most important piece a layout is built around, usually the sofa, bed or dining table. Everything else is sized and placed relative to it.

Grounding

Grounding is visually tying a group of furniture together so it reads as one zone. A rug is the usual tool, but light, a change of floor or a ceiling feature can do it too.

Patina

Patina is the change a surface takes on through age, light and use. Some materials improve with it; others just wear.

Martindale

Martindale is the standard abrasion test for upholstery fabric, counted in rub cycles before visible wear. The higher the count, the longer the fabric survives daily use.

Electricals 10

First fix

First fix is the stage when cables, pipes and back boxes go in, before walls are plastered and floors finished. After it, moving a socket or light point means cutting into finished surfaces.

Layered lighting

Layered lighting combines ambient, task and accent light from several sources at different heights. Each layer is switched or dimmed on its own so the room can change mood.

Ambient light

Ambient light is the general background light that lets people move around safely. It sets a room’s overall brightness but rarely its character.

Task light

Task light is focused light for a specific activity: reading, cooking, working. It is brighter than ambient light and aimed at the work surface.

Accent light

Accent light is directional light that picks out an object or surface: art, texture, a plant. It works by contrast, so its surroundings must be dimmer.

Wall washing

Wall washing lights a wall evenly from fittings set back from it, usually in the ceiling. Because we judge brightness by vertical surfaces, a washed wall makes the whole room feel brighter and larger.

Colour temperature

Colour temperature describes how warm or cool white light looks, in kelvin (K). Lower is warmer: a warm home bulb is about 2700 K, daylight roughly 5000–6500 K.

CRI

CRI (colour rendering index) measures how faithfully a light shows colours compared with a reference light, on a scale up to 100. Low-CRI light makes wood, fabric and skin look dull or grey.

Lux

Lux measures how much light falls on a surface, in lumens per square metre. It is what a light meter reads, and different tasks need different levels.

Lighting scene

A lighting scene is a preset combination of circuits and dim levels, recalled with one switch or button. Typical living-room scenes are day, evening and late.

Plumbing 5

Soil stack

The soil stack is the vertical pipe that carries waste from WCs and sinks down to the drain, and vents the system above the roof. Every WC needs a short, falling route to it.

Fall

Fall is the slope a waste pipe needs so water drains by gravity, written as a ratio or millimetres per metre. Without enough fall, pipes block and smell.

Thermostatic valve

A thermostatic valve mixes hot and cold to a set temperature and holds it when pressure changes elsewhere in the house. It stops a shower scalding when someone runs a tap.

Wet room

A wet room is a bathroom where the shower floor is level with the rest and the whole room is waterproofed (tanked) and drains to a floor gully. There is no tray and often no screen.

Underfloor heating

Underfloor heating runs warm-water pipes or electric mats under the floor finish, so the whole floor becomes a low-temperature radiator. It frees the walls of radiators.

Joinery & millwork 5

Carcass

The carcass is the box structure of a cabinet: sides, base, top and back. Doors, drawers and fronts hang on it, and they carry the look.

Scribe

A scribe is a strip of material left oversized and cut on site to follow an uneven wall, floor or ceiling. It is how fitted joinery meets an imperfect building without gaps.

Plinth

The plinth is the recessed base under cabinets, also called a kickboard or toe kick. It lets you stand close to the worktop without kicking the doors.

Shelf span

Shelf span is the unsupported length of a shelf between its supports. Longer spans and heavier loads make shelves sag over time.

Millwork

Millwork is the decorative finishing timber of a room: skirtings, architraves, cornices, panelling and mouldings. In the UK it is usually grouped under joinery.

Openings 5

Door schedule

A door schedule is the table that lists every door on a project, each with a reference (D01, D02…) that matches the plan. It records size, swing, leaf and frame finish, ironmongery and any fire or acoustic rating.

Window schedule

A window schedule lists every window with its reference (W01, W02…), opening size, sill and head heights, glazing, opening type and frame finish. It sits beside the elevations rather than replacing them.

Structural opening

A structural opening is the raw hole in the wall, before frames, linings and plaster go in. It is always larger than the finished door or window it receives.

Ironmongery

Ironmongery is the hardware on doors and windows: handles, hinges, locks, stops, closers and pulls. It is the part of an opening people touch every day.

Threshold

A threshold is the transition at the foot of a doorway, where floor finishes, levels and seals meet. It decides whether a door is level, draught-proof and step-free.

Finishing 4

Hanging line

A hanging line is a shared centre height for art, so pieces of different sizes still align. Galleries typically use about 145–150 cm from the floor, close to average eye level.

Fullness

Fullness is the ratio of curtain fabric width to the width of the track or pole. More fullness means deeper folds and a richer drape.

Vignette

A vignette is a small composed group of objects on one surface: a console, a shelf, a side table. It works like a still life, with varied heights, a clear hierarchy and space around it.

Editing

Editing is removing pieces until every remaining one earns its place. It is usually the last step of a good room, and the hardest one for clients.

Rendering 4

Ambient occlusion

Ambient occlusion darkens the places ambient light struggles to reach: corners, the gap under a sofa, the line where furniture meets the floor. It is what makes objects look grounded rather than pasted on.

Global illumination

Global illumination simulates light bouncing between surfaces, so a white wall lifts the shadows beside it and an oak floor warms the ceiling. Without it, renders look harsh and flat.

PBR material

A PBR (physically based rendering) material describes a surface with real-world properties: base colour, roughness, metalness and bumps. It behaves correctly under any light.

Camera height

Camera height is how high the virtual camera sits for an interior view. Too high and the room looks like a plan; too low and furniture looms.

Units