Home Extension Drawings Explained: Plans, Elevations, Sections
- Jun 9
- 5 min read
If you're applying for planning permission, getting a builder to quote, or just trying to understand what your architect has sent you, the drawing pack for a home extension is the most important document you'll see.
We're a Kettering-based team that designs and builds home extensions in Northamptonshire. Here's a clear guide to the full pack of drawings a home extension needs, what each one shows, and why it matters. With real examples from a single storey rear extension we recently completed.
What drawings do you need for a home extension?
A standard home extension drawing pack includes existing drawings (plans and elevations of the house as it currently is), proposed drawings (plans and elevations showing the extension), sections (cuts through the building showing construction), a site plan, a location plan, and a block plan. Together they cover everything planning officers, building control inspectors and contractors need to assess and build the extension.
The exact pack depends on the council, the size of the extension, and whether you're going through full planning permission or relying on permitted development. As a rule, you'll need:
Existing drawings. Plans and elevations showing the house as it stands today.
Proposed drawings. Plans and elevations showing the house with the extension built.
Sections. Vertical cuts through the building showing how it's put together.
Site plan. Your property and its immediate surroundings, usually at 1:200 or 1:500.
Location plan. A wider zoomed-out plan, usually at 1:1250, showing the property in context.
Block plan. The position of buildings within the site boundary.
Construction notes. Technical specifications for materials, foundations, insulation, drainage and so on.
Below we walk through each in turn, with real examples from a recent project.
Existing drawings
Existing drawings show the house as it currently stands. They're produced from a measured survey, where the designer or a surveyor visits the property and records every wall, window, door and ceiling height.
Most planning applications require both existing and proposed drawings side by side, so the council can see exactly what's being changed. Existing drawings usually include:
Existing floor plans, one for each storey
Existing elevations, one for each face of the property (typically four)
Existing sections, if the project affects the structure significantly
Skipping or skimping on existing drawings is a common reason for planning applications being rejected as invalid. The council needs the existing condition to assess the impact of the proposal.
Proposed plans and elevations
Proposed plans and elevations are the drawings most homeowners picture when they hear "extension drawings". They show the house as it will look once the extension is built.
The proposed ground floor plan shows the new layout: where the walls go, where doors and windows are positioned, where the kitchen, dining or living spaces sit. The elevations show each face of the property with the extension included. What it will look like from the rear garden, from each side, and from the front if affected.
The drawing above is from a single storey rear extension project we recently completed. The plan (top left) shows the ground floor with new extensions added to the rear of the property, including a rear entry hall with level access for wheelchair users. The rear elevation (top right) shows the back of the house with the new windows and roofline. The two side elevations show how the extension reads from either neighbour's perspective. Notes around the drawings flag the specific decisions: extension set back 100mm from the boundary fence, existing doors re-used, level access at the rear, existing inspection chamber relocated.
Planning officers spend most of their time on the proposed plans and elevations. They want to see scale, massing, materials, and impact on neighbours. These drawings carry the weight of the application.
Sections and construction notes
Section drawings cut vertically through the building. They show how the floor, walls, ceiling and roof are built, and how each layer connects to the existing structure. A good set of sections demonstrates that the extension will meet current building regulations: insulation thicknesses, foundation depths, drainage routes, structural connections.
The drawing above shows the section drawings and construction notes from the same project. Section A-A and Section B-B cut through different parts of the extension, showing the foundation depths, cavity wall construction, insulation layers, roof build-up, and connection to the existing house. The notes column on the left specifies every material and standard the build has to meet, from the 150mm cavity insulation in the external walls, to the 300mm of loft roll insulation in the pitched roof, to the radon sump below the floor slab.
Building control inspectors live in these drawings. They want to see that every part of the extension meets the relevant regulation: Part L for energy efficiency, Part A for structure, Part H for drainage, Part K for safety glazing.
This level of detail is also what separates a buildable drawing from a pretty one. If the sections aren't right, the builder either has to interrupt the build to fix decisions on site, or the work fails inspection later.
If you're planning a double storey extension drawings set, the sections become more important still, because the upper floor's structure, fire separation and stair details all need to be drawn out before any concrete is poured.
Site plan, location plan and block plan
These three context drawings are mandatory for any planning application. They show the council where your property sits and what surrounds it.
Location plan. Usually at 1:1250 scale. Shows your property edged in red, with at least two named roads visible. Sourced from Ordnance Survey or a paid plan supplier.
Site plan. Usually at 1:200 or 1:500 scale. Shows your property and the immediate area in more detail, with the proposed extension footprint indicated.
Block plan. Shows the buildings within your site boundary and their relationship to one another. Often combined with the site plan on smaller projects.
Most councils require all three, plus the proposed and existing drawings, before they'll validate an application. Missing any of them sends your application back to the start.
Planning drawings vs building regulation drawings
There's an important distinction here that catches a lot of homeowners out.
Planning drawings are produced for the planning application. They focus on appearance, scale, impact on neighbours, and adherence to local planning policy. They're usually drawn at 1:100 or 1:50.
Building regulation drawings are produced for building control. They focus on technical compliance: structure, insulation, fire safety, drainage, glazing. They're usually drawn at 1:50 with detailed sections and construction notes.
Most extensions need both. The planning drawings come first, and the building regulation drawings follow once planning is granted. Some designers produce one combined set; others split them. Either way, you need both before any work can start on site.
Planning permission takes 8 weeks from validation in the standard case. Building regulation approval can run in parallel or follow after.
Who produces home extension drawings?
The three main routes for getting drawings produced:
An architect. RIBA-chartered, charges a percentage of construction cost. Best for design-led, complex or sensitive projects. The most expensive option.
An architectural technologist or designer. Cheaper than a full architect. Produces fully compliant drawings for standard projects. The most common route for typical UK home extensions.
A draughtsperson or CAD designer. The cheapest option. Produces functional drawings to a brief. Best when you already have a clear design in mind and just need it documented.
Whichever you choose, ask to see examples of completed projects. Drawings that have actually been built, and that have passed planning and building control, are the test.
Get a quote for an extension in Northamptonshire
If you're planning an extension in Kettering or anywhere else in Northamptonshire and want one team to handle the drawings, planning and build, speak to our team. Finance is available through Phoenix Financial Consultants if you'd rather spread the cost.
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