What Drawings You Need for a Double Storey Extension: A Builder's Guide

You're planning a double storey extension. Maybe a quote has come back and the word "drawings" keeps appearing. Maybe an architect has talked you through a fee proposal and you're trying to work out what's standard, what's optional, and what your builder actually needs to start work.

We're a Kettering-based team that designs and builds home extensions across Northamptonshire. We produce these drawings in-house and use them on site every week. Here's a plain-English run-through of what you need, who produces it, when, and what it tends to cost.

What drawings do you need for a double storey extension?

A double storey extension typically needs three sets of drawings: planning drawings (submitted to your local council for planning permission), building regulations drawings (for building control approval), and structural calculations (produced by a structural engineer). Each set has a different purpose and arrives at a different stage of the project.

All three are needed before construction starts. They aren't optional, and skipping a stage usually means delays, rework, or being asked to expose finished work months later so it can be inspected.

The four sets of drawings, explained

Existing drawings (the measured survey)

These show what's already there. Existing room layouts, floor and ceiling heights, doors, windows, external walls and roof lines. Everything else gets designed off these, so they need to be accurate. A measured survey usually takes half a day on site, and the drawn-up version arrives within a week.

Planning drawings

The formal package submitted to your local council for planning permission. The set typically includes:

• A location plan (1:1250 scale, showing where the property sits in the area)

• A site or block plan (1:500 scale, showing the property within its plot)

• Existing floor plans, elevations and sections

• Proposed floor plans, elevations and sections of the extension

The council uses these to decide whether the extension is acceptable from a planning point of view. The look, the size, the impact on neighbours, the loss of light, how it sits within the street. Almost all double storey extensions need planning permission. Permitted development rights rarely apply to two-storey work.

Building regulations drawings

A more technical package showing how the extension will actually be built. They cover insulation specifications, fire safety, drainage, ventilation, glazing performance, foundations, structural elements, and how each junction is detailed. Electrical and plumbing layouts are often included in this set on domestic projects.

These are reviewed by a building control surveyor (either the council's own team or an approved private inspector) to confirm the build complies with the current building regulations. Dry to read, but essential. They protect the homeowner and become evidence of compliance when you sell.

Structural calculations

Produced by a structural engineer, not the architect or builder. They cover the loads on key elements: steel beams, foundations, masonry, lintels. They're required because a double storey extension changes how loads travel through your home.

We commission these from independent structural engineers on every two-storey job.

The beginning of a double storey home extension in Irthlingborough

Planning drawings vs building regulations drawings

This is the most common point of confusion. Planning approval and building regulations approval are not the same thing, and the drawings serve different purposes.

Planning drawings are about what the building looks like and where it sits. They get submitted before any work starts, and the council reviews them against local planning policy.

Building regulations drawings are about how the building is constructed. Building control checks them to confirm the structure, fire safety, insulation, drainage and ventilation all meet current standards.

You can technically apply for building control approval after planning has been granted, but it's smarter to have both packages ready together. It avoids redesigning details twice and stops the build losing time waiting for paperwork. The Planning Portal publishes the official guidance on both processes if you want to read the formal rules.

Who produces double storey extension drawings?

There are several routes, each with different strengths.

An architect. A RIBA-registered architect produces planning and building regulations drawings, typically charging a percentage of the construction cost.

An architectural technician or designer. Cheaper than a full architect. Produces compliant drawings without the design flair or in-depth planning negotiation.

A structural engineer. Engaged in addition to whichever option above, for the calculations.

How long does it take to get the drawings ready?

For a standard double storey extension, a realistic timeline is:

• Survey and proposed drawings: 2 to 3 weeks

• Planning application (drawings prepared plus council decision period): 8 to 12 weeks total

• Building regulations drawings: 2 to 4 weeks

That's three to four months from first sketch to having everything signed off, before any spades go in the ground. Compressing this rarely works. Councils can take their full eight weeks to determine a planning application, and they often do. If the council comes back with objections or requests amendments, add another four to eight weeks.

How much do double storey extension drawings cost?

Costs depend on the size of the extension, the complexity of the design, and who produces them. As a rough UK guide:

• Architect (planning + building regs drawings): 8 to 12% of construction cost

• Architectural technician: 2 to 5% of construction cost

• Structural engineer: £600 to £1,500 for a standard job

• Planning application fee: £258 (England, householder application)

• Building control application fee: typically £500 to £1,000

Get a quote for a double storey extension in Northamptonshire

If you're planning a two-storey home extension in Corby, or anywhere else in Northamptonshire, speak to our expert team about what you're looking for. We'll come back with a realistic figure and timeline. Finance is available through Phoenix Financial Consultants if you'd rather spread the cost.