Architectural Drawings for London Home Projects: What You Need and When

Architectural drawings are produced in a sequence of stages, each with increasing detail and information. Understanding the stages helps you know what you are commissioning and what you have received.

RIBA Plan of Work: the Royal Institute of British Architects Plan of Work is the standard project process framework used in UK construction. It has eight stages (0–7) from Strategic Definition through Handover. For a typical London residential project, the most relevant stages are:

Stage 1 — Preparation and Briefing: defining what the project is, the client's requirements, the site, and the procurement strategy. No drawings at this stage — it is a briefing and information-gathering stage.

Stage 2 — Concept Design: initial design concepts explored and developed. Drawings at this stage are schematic — floor plans, section sketches, and study models — showing the spatial arrangement and design intent but not full dimensional accuracy. Used to agree the design direction before committing to detailed design.

Stage 3 — Spatial Coordination (formerly Design Development): the design is developed to full geometric accuracy. All spaces are properly dimensioned; the structural strategy is coordinated with the architecture; the envelope (wall, roof, and floor specifications) is defined. These are the drawings typically used for a planning application.

Stage 4 — Technical Design (Working Drawings): the fully detailed drawings used for Building Control submission and contractor pricing. Include structural details, drainage, M&E layout, specification of all materials and finishes, door and window schedules, and construction details.

Stage 5 — Manufacturing and Construction: the actual construction information issued to site — shop drawings, subcontractor coordination, site instruction drawings. Produced during construction in response to specific site conditions.

A planning application for a householder extension or loft conversion in London requires a defined set of drawings. Understanding exactly what is required avoids wasted cost (commissioning too much) or application refusal (submitting too little).

Site location plan (scale 1:1250 or 1:2500): shows the application site in the context of the surrounding area — streets, neighbouring buildings, and site boundary (typically red-lined). Usually produced from an Ordnance Survey base map. Required for all planning applications.

Existing and proposed block plan (scale 1:500): shows the site and immediately adjacent land, with the building footprint on the site (existing and proposed). Required where the proposal changes the footprint.

Existing plans (scale 1:50 or 1:100): floor plans of the existing building (as-built), showing all rooms, walls, windows, doors, staircases, and dimensions. These must be a true record of the existing building, not an assumed or desk-study plan.

Proposed plans (scale 1:50 or 1:100): floor plans showing the proposed changes — new rooms, demolished walls (typically shown hatched), and new walls (shown solid or hatched differently). All new and existing elements must be clearly distinguished.

Existing and proposed elevations (scale 1:50 or 1:100): elevations of all affected external elevations (the elevation to which the extension is attached, and the elevations from which the extension is visible). Elevations show the full height of the building, materials, window positions, and relationship to adjacent buildings.

Existing and proposed sections (sometimes required): cross-sections through the building and extension, showing floor-to-ceiling heights, roof pitches, and the relationship between the new and existing volumes.

Design and access statement: for applications in conservation areas or for larger schemes, a written explanation of the design approach and how it responds to the site and local context.

Building Control drawings are required for Building Regulations approval (Full Plans application) or for the inspector's reference during construction (Building Notice route). They contain significantly more information than planning drawings.

Structural information: foundation design and specification; structural steel schedules (UB/UC sizes, lengths, connections); structural timber specification (floor joist size, spacing, span tables reference); and lintels schedule. This information is typically produced by a structural engineer and incorporated into the architectural drawing set.

Thermal specification: wall, roof, and floor U-value calculations; insulation specification (product, thickness); thermal bridging analysis at junctions; and evidence of compliance with Part L of Building Regulations.

Fire safety information: escape route plans; fire door positions; smoke alarm layout; and fire protection of structural elements where required.

Drainage: drainage layout plan showing internal drainage runs, locations of inspection chambers, gradients, and connection to the public sewer or surface water drainage system. Sanitary fitting positions and waste pipe routes.

Ventilation: mechanical ventilation locations; duct routes; and confirmation of compliance with Part F.

M&E (mechanical and electrical): electrical layout (socket positions, lighting points, circuit breakdown, consumer unit); plumbing schematic (hot and cold water, heating flow and return, boiler or heat pump); and underfloor heating layout if applicable.

Construction details (scale 1:10 or 1:5): large-scale details at critical junctions — wall head, cill, and jamb details at windows; eaves details; parapet details; threshold details at doors; and junction between new and existing construction. These details are essential for Building Control compliance and for the contractor to build correctly.

A measured survey of the existing building is the starting point for all architectural drawings. It is a systematic measurement of the building as it actually exists — floor plan dimensions, ceiling heights, wall thicknesses, window and door positions, and external dimensions.

Why a measured survey matters: many older London houses were built with minor variations from the theoretical design — rooms are slightly off-square, walls are not perfectly plumb, ceiling heights vary from room to room. If architectural drawings are based on assumed or desk-study dimensions rather than actual measurements, errors and discrepancies will appear during construction.

How measured surveys are carried out: traditionally by tape measure and laser distance meter, with the measurements recorded on sketch plans and then transferred to CAD. Increasingly, 3D laser scanning (LIDAR) is used for complex or larger buildings — a scanner set up at multiple positions captures millions of data points that are processed into a precise 3D point cloud from which accurate drawings can be produced.

Who carries out the survey: the architect may carry out the measured survey themselves (included in their fee), or may commission a specialist measured-survey company. For simple residential projects, the architect typically does the survey. For more complex or larger properties, a specialist surveyor is more efficient.

Timing: the measured survey should be completed before any design work begins. Designing without measured survey data leads to designs that may not fit the existing building, requiring expensive revision at a later stage.

Architectural drawings are produced at defined scales — the ratio between the drawing dimension and the real-world dimension.

Common scales in residential architectural drawings:

1:1250 — site location plan (very small scale, large area context) 1:500 — block plan / site plan 1:100 — general arrangement plans and elevations (showing room layouts, window positions) 1:50 — more detailed plans and elevations (the standard scale for planning drawings) 1:20 — detail drawings for windows, doors, and thresholds 1:10 or 1:5 — construction details (showing layer-by-layer wall and roof construction)

What each scale tells you: at 1:100, a 5m room is drawn as a 50mm line on the drawing — room layouts, proportions, and overall dimensions are visible. At 1:10, a 200mm thick wall is drawn as a 20mm line — the individual components within the wall construction can be shown and dimensioned.

Scales for Building Control vs planning: planning drawings are typically 1:100 or 1:50. Building Control technical drawings include large-scale details at 1:10 or 1:5. If you have received drawings that are only 1:100 or 1:50, you have planning-level information, not construction-level information — a contractor cannot build accurately from these alone.

As-built drawings: at the end of the project, as-built drawings record what was actually constructed (which may differ from the design drawings due to site changes). As-built drawings are important for future reference — for subsequent building work, insurance purposes, and sale.