What drawings do I need for a house extension?
An extension needs more than a picture of the finished house. The right drawing package records what is there, explains what will change and develops the details needed for the next stage.
For projects in England. Requirements depend on the property, proposal and application route; check the current local authority requirements for your site.
Start with the building you have.
A measured survey provides a reliable starting point for the design. Existing floor plans, elevations and relevant sections record the layout, external appearance and levels. Old estate-agent plans can help explain your ideas, but their dimensions and detail may be insufficient for design work.
Agree what the survey includes. Access, changes in level, visible structure, boundaries and drainage may need further investigation. A measured drawing does not establish the condition of hidden structure or replace specialist surveys.
Show what you want to change.
A typical extension drawing package may include a location plan, site or block plan, existing and proposed floor plans, elevations and sections. Floor plans show the arrangement of spaces; elevations show the outside of the building; sections explain heights and relationships between levels.
For a planning application in England, government guidance requires a location plan and, in most cases, additional drawings describing the development. Drawings need an identified scale; plans must show north. The local authority’s validation requirements determine what else is needed for your proposal.
Check the planning route early. Some extensions may fall within permitted development rights, subject to conditions and restrictions. That does not remove the need to consider building regulations or other applicable consents.
What an elevation tells you.
Our Billericay residential design study pairs existing and proposed front elevations. Comparing them makes changes to the entrance, roof forms and window arrangement easier to discuss than a render alone. The exterior visualisations then help communicate the proposed appearance.
This is an example of how a drawing communicates change, not a complete extension application package. The sheet is labelled Preliminary; it does not establish planning approval or completed construction.
Explore the Billericay design studyThen resolve how it will be built.
Once the design direction is established, technical drawings and specifications develop matters such as construction build-ups, insulation, drainage, ventilation and relevant fire safety requirements. Structural design and calculations may require a structural engineer. The package needs coordination between the appointed designers.
Planning permission and building regulations approval are different; a project may need both. Planning drawings alone should not be assumed to provide everything a contractor needs to price or build the work. Agree whether tender information, construction details and support during building are included in your appointment.
Source: GOV.UK — building regulations approval. Read our comparison of the two drawing stages.
Before commissioning your drawings.
- Share the address, existing drawings, photographs and any previous planning decisions.
- Describe the rooms or improvements you need, your budget range and intended timing.
- Ask which surveys, drawing stages and applications the fee covers.
- Confirm who appoints specialists and whether their fees, application fees and revisions are included.
- Ask what information will be ready for the contractor, and what remains to be developed.
You do not need a finished design brief to start. Clear priorities help scope the first stage around your property.
Tell us about your project.
Share the property, what you want to change and how far you have got. We can discuss the architectural work needed for the next stage.
Tell us about your project