Planning a home extension is exciting. It is also one of those projects where the paperwork matters just as much as the design itself.
Before your builder can price the work properly, before your local authority can assess your application, and before building control can approve the technical details, you will need the right set of drawings.
The exact drawings depend on the size, location and complexity of your extension. A simple rear extension will usually need less detail than a two-storey extension, a listed building project or work in a conservation area. Even so, most projects follow a similar route: existing drawings, proposed plans, planning drawings, building regulations drawings and, where needed, structural information.
Here is what homeowners usually need to prepare.
Existing drawings show your home as it stands now. They normally include existing floor plans and elevations, showing the current layout, walls, doors, windows, roof form and external appearance.
These drawings are useful because they give everyone a clear starting point. Your designer can see what is being altered, your local planning authority can compare the current building with the proposal, and your builder can understand the scope of change.
For many projects, a measured survey is the first step. This helps ensure the drawings are accurate before design work begins.
Proposed floor plans show how the extension will change your home. These plans set out the new layout, including walls, openings, doors, windows, kitchen arrangements, utility spaces and circulation through the house.
This is often where homeowners start to see how the extension will actually work day to day. A good plan is not only about adding space. It should consider light, movement, storage, connection to the garden and how the new area relates to the rest of the home.
For planning purposes, proposed plans help the local authority understand the scale and layout of the development. For builders, they help form the basis of pricing and construction.
Elevations are drawings of the outside of the property. They usually show the front, rear and side views of the house, both existing and proposed.
These drawings are particularly important for planning applications because they show how the extension will look from the outside. They include details such as roof shape, window positions, door openings, external materials and overall height.
If your extension is close to neighbouring properties, elevations can also help explain its relationship with boundaries, outlook and privacy.
A location plan shows where your property sits in relation to surrounding roads, plots and buildings. A block plan gives a closer view of the site, including boundaries, access, nearby structures and the position of the proposed extension.
These are typically required for planning applications and lawful development certificate applications. They help the local authority assess the proposal in context, rather than looking at the extension in isolation.
A roof plan may be needed where the roof design is more involved. This can show ridges, valleys, rooflights, flat roof areas, drainage falls and how the new roof connects to the existing building.
This is especially useful for side returns, wraparound extensions, two-storey extensions and projects where water drainage or roof junctions need careful thought.
Sections cut through the building to show height, structure and build-up. They may include floor levels, ceiling heights, foundation depths, roof construction and insulation.
Detail drawings go a step further. They show how specific junctions are built, such as where a flat roof meets an existing wall, how damp proofing is handled, or how insulation continues through a floor or roof.
These drawings become more important at the building regulations stage, when the focus moves from what the extension looks like to how it will be built safely and correctly.
Planning drawings are used to support a planning application or a lawful development certificate. They usually include existing and proposed plans, elevations, site plans and sometimes sections.
Their purpose is to show the size, scale, appearance and impact of the extension. Planning drawings are not usually detailed enough for construction. They are there to help the local planning authority decide whether the proposal is acceptable in planning terms.
Some extensions fall under permitted development, meaning a full planning application may not be needed. However, it is often sensible to apply for a lawful development certificate, as this gives formal confirmation that the work was lawful at the time it was carried out.
Building regulations drawings are different from planning drawings. They are technical documents that show how the extension will comply with building standards.
They can cover structure, insulation, ventilation, fire safety, drainage, electrics, accessibility and energy performance. These drawings are submitted to building control, either through the local authority or an approved inspector.
Even if your extension does not need planning permission, it will usually still need building regulations approval. This is a common point of confusion. Planning deals with whether you can build. Building regulations deal with whether it is built safely and properly.
Western Building Consultants support clients with building regulations applications, technical specifications and plans, helping turn early design ideas into buildable, compliant details.
If your extension involves steel beams, removing load-bearing walls, new foundations, large openings or significant roof changes, structural information will usually be needed.
A structural engineer may provide calculations and drawings showing beams, lintels, columns, padstones, joists, rafters and foundation requirements. These are used by building control and your builder.
Skipping this stage can lead to delays, redesigns or problems on site. It is far better to resolve structural questions before work begins.
Yes. Clear drawings help builders price the job accurately and reduce assumptions. Without proper drawings, quotes can vary widely because each builder may be interpreting the project differently.
Good drawings also reduce the chance of disputes during the build. Everyone can work from the same information, with fewer grey areas around specification, layout and detail.
Most home extensions will need:
The right package depends on the property and the type of extension. A modest single-storey rear extension may be relatively straightforward. A two-storey extension, listed building, conservation area property or complex structural alteration will need more detailed input.
At Western Building Consultants, we help homeowners move from early ideas through to planning, technical design and building regulations approval. With architectural, surveying and technical expertise under one roof, we can guide your project from concept to completion with clear advice at each stage.
The right drawings can save time, reduce uncertainty and help your project move forward with fewer delays. Western Building Consultants can prepare the plans and technical information you need for planning, building regulations and construction.
Get in touch with our team to discuss your extension and find out what drawings your project will need.