The interior design guide
Open Rayon

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.

Get startedKnowledge base

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.

Open the Lexicon

Use the guide in your AI assistant.

Connect Claude or ChatGPT.

The guide has an MCP server, so your assistant can search it, read its pages and cite them while it answers you. It is free, read-only, and needs no account or key.

Connect to Claude
Open docs
All sections

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.

Keep reading.

Where to go next.

Sections.

Keep reading.

Where to go next.

Survey,

measuring what is there.

Every design starts from the space as it is. A survey records its dimensions, shape, details and condition; the record is then redrawn as a clean plan. Done well, everything designed afterwards fits.

Survey.

Capture the space.

Record the room’s dimensions, geometry, architectural details and existing condition. Three techniques do it, each with its own equipment and accuracy. Choose one, or combine them: a scan for the whole, a laser meter for what must fit.

Manual surveySmartphone LiDARProfessional 3D scanning

Manual survey.

Pen, paper and a laser meter.

The traditional method, still the most reliable for a single measurement. A laser distance meter measures by bouncing a beam off the far surface; a tape does for short runs.

  1. Step 1: Sketch the room

    Draw the plan roughly, on paper or a tablet: walls, doors, windows, recesses and anything fixed. It needs no scale, only the room's proportions, and enough space around it to write the numbers.

  2. Step 2: Measure the perimeter

    Start at the entrance and work clockwise round the room, one wall after another, so nothing is skipped and every figure has its place on the sketch.

  3. Step 3: Record the dimensions

    Write the overall length of each wall, then the segments that make it up: from the corner to each opening, the opening, and on. Add recesses, projections and wall thicknesses at doorways.

  4. Step 4: Locate the services

    On the same dimensioned sketch, mark the sockets, switches, radiators, visible pipes and ventilation outlets, each with its distance from a corner and its height.

  5. Step 5: Measure the heights

    Record the floor-to-ceiling height in several places, then door and window heights, sill heights, skirtings, cornices and any change of level. Each height is measured from the finished floor.

Smartphone LiDAR.

A scan in your pocket.

LiDAR measures distance with pulses of light. Recent iPhones and iPads carry the sensor, and apps built on Apple’s RoomPlan recognise walls, doors, windows and furniture as they scan, and draw a floor plan from them.

  1. Step 1: Prepare the room

    Open the inside doors, draw back curtains and move what you can away from the walls. A scanner can only record what it can see.

  2. Step 2: Scan the space

    Walk slowly round the room with the phone at chest height, pointing it at the walls, floor, ceiling, doors and windows. Keep moving steadily: quick turns leave gaps.

  3. Step 3: Cover every viewpoint

    Point the phone into each corner, recess and opening. Alcoves and the far sides of furniture are where scans most often leave geometry out.

  4. Step 4: Verify the measurements

    Check the dimensions that matter with a laser meter: overall lengths, openings, and anything fitted. Where the scan and the meter disagree, the meter wins.

Professional 3D scanning.

Laser scanners and capture platforms.

For large spaces, complex buildings and detailed records. A terrestrial laser scanner stands on a tripod and measures millions of points around it.

  1. Step 1: Plan the scan positions

    Choose positions that see every room and corridor, with each scan overlapping the next so they can be joined. Mark them on a sketch plan.

  2. Step 2: Align the scans

    Join the separate scans into one, a step called registration. Software matches the shapes the scans share, or targets placed in the room, until the scans sit together.

  3. Step 3: Generate the spatial data

    Produce what the project needs: a navigable 3D capture, a point cloud (the room as millions of measured points) or a mesh, its surface as triangles.

  4. Step 4: Extract the drawings

    Cut the point cloud with a horizontal plane, about 1 m above the floor, to get a plan; vertical cuts give sections and elevations. Draw over the cut, rather than tracing every point.

Plan reconstruction.

From survey to a clean CAD plan.

Turn the survey into an accurate, editable floor plan in Rayon. The order matters: scale first, then structure, then annotate.

  1. Step 1: Import and set the scale

    Bring the survey into Rayon: a DWG or DXF from a surveyor or scanning app, or a PDF, PNG or JPEG of a sketch or exported plan. At Import scale, draw a line over something you measured, a door is good, and type its real length.

  2. Step 2: Organise the drawing

    Put each kind of element on its own layer: walls, doors and windows, structure, fixtures, services, dimensions and annotations. Rayon's Layers carry colours and styles, so one change restyles every element on a layer.

  3. Step 3: Add the annotations

    Name each room and give its area, mark ceiling heights, and add the dimension strings the next phase needs, using Linear dimension, Text and Tag.

Checklist.

Before the design begins.

Go through both lists before programming starts. A dimension missed now costs far more to correct once the design depends on it. Your ticks are kept in this browser, so you can come back to them on site.

Survey

Plan reconstruction

Keep reading.

Where to go next.

Previous

2 · Running a project

Next

3 · Surfaces

Questions.

What people ask most about surveying.

How do you measure the square footage of a room?

Measure the length and the width of the floor and multiply them: a room 4.80 m by 3.60 m is 17.3 m², or about 186 sq ft (1 m² is 10.76 sq ft). Split an L-shaped or irregular room into rectangles, work out each one and add them. Measure between the finished walls, at floor level, and leave out chimney breasts and other projections.

How do you measure a room for a floor plan?

Sketch the room first, then measure clockwise from the door: each wall’s overall length, then the segments to and across every opening. Add the depth of recesses and projections, both diagonals to check the corners, and the ceiling, sill and door heights. A laser distance meter does it faster and more precisely than a tape.

How do you draw a floor plan from measurements?

Draw the longest wall first at scale, usually 1:50 for a room, then add the others in the order you measured them, checking each corner against the diagonals. Draw the walls with their thickness, place the openings by their distances from the corners, and finish with door swings and dimensions. In CAD, import a scanned or photographed sketch and set its scale from one known length before tracing.

What is a floor plan?

A floor plan, or plan, is a drawing of a room or building seen from above, as if cut horizontally about 1.2 m above the floor. It shows walls, doors, windows and fixed elements at scale, with their dimensions, and is the base for every other drawing of the project.

What is the standard ceiling height?

In most new homes, ceilings are between 2.40 and 2.60 m high; older houses often have 2.70 to 3.00 m or more on the main floors. Building rules set a minimum, commonly around 2.20 to 2.50 m for habitable rooms, but the figure varies by country, so check the local code. Always measure the real height in several places: floors and ceilings are rarely level.

What are as-built drawings?

As-built drawings record a building as it was actually built, including every change made on site, and are handed over at the end of a project. A measured survey of an existing building produces something similar, existing-condition drawings, which are the starting point for any new design.

What is LiDAR?

LiDAR (light detection and ranging) measures distances by sending out pulses of light and timing how long each takes to bounce back. Repeated thousands of times a second in every direction, it builds a 3D record of a space. Phones and tablets use a small LiDAR sensor; survey scanners use far more powerful ones.

Which iPhones have a LiDAR scanner?

The Pro and Pro Max iPhones have one, from the iPhone 12 Pro onward, as do iPad Pro models from 2020. The standard and Plus models do not. Apps built on Apple’s RoomPlan use it to scan a room and draw its floor plan.

What is Matterport?

Matterport is a platform for capturing buildings as navigable 3D models, often called digital twins, viewed online. It works with its own cameras, with some phones, and with laser scanners. Its measurements are only as reliable as the device used: a 360° camera capture is a good visual record, a laser scan a measured one.

What is a point cloud?

A point cloud is the raw result of a 3D scan: millions of measured points, each with its position and often its colour, that together describe the surfaces of a space. Drawings are made from it by cutting it with planes, horizontal for plans, vertical for sections and elevations, and drawing over the cut.

Units