What Are Building Regulations Drawings and What Should They Include?

You have designed your extension.

Perhaps planning permission has been granted, or you have established that the work can proceed under Permitted Development.

The builder is now asking for drawings.

This is where homeowners often discover that planning drawings and Building Regulations drawings are not the same thing.

Building Regulations drawings take the architectural proposal into its technical stage.

Rather than principally showing what the building will look like, they develop and communicate how the proposed work is intended to satisfy the applicable technical requirements and how key parts of the construction relate to one another.

For a typical extension, loft conversion or substantial alteration, that can involve considerably more information than was needed for planning.

Planning drawings generally establish matters such as:

• existing and proposed layout;

• size and position of an extension;

• external appearance;

• roof form;

• windows and doors; and

• relationship with the existing property.

Those drawings allow a planning proposal to be understood.

They do not necessarily resolve how the building will be constructed.

Building Regulations address a different set of questions.

These can include:

• structure;

• fire safety;

• resistance to moisture;

• ventilation;

• sanitation;

• drainage;

• thermal performance;

• access;

• electrical safety; and

• other requirements relevant to the particular project.

That is why obtaining planning permission should not normally be treated as the end of the design process.

For many projects, it marks the transition from planning design into technical design.

There is no universal drawing checklist that applies identically to every project.

The information must suit the work being proposed.

Current local-authority Full Plans requirements demonstrate this. Kingston requires technical design drawings and an associated Building Regulations specification, while Enfield identifies relevant floor plans, elevations, cross-sections, specifications and calculations.

Chelmsford's current guidance similarly calls for existing/proposed plans and elevations, a vertical construction section, drainage information and a specification explaining how compliance will be achieved.

For a typical domestic project, the technical package might therefore contain the following.

Proposed Floor Plans

The proposed plans develop the architectural arrangement.

Depending upon the project they can identify:

• wall construction;

• openings;

• doors;

• windows;

• structural elements;

• ventilation provisions;

• drainage;

• room uses;

• stairs; and

• other relevant technical information.

They are not merely a duplicate of the planning floor plan.

Technical Sections

Sections are particularly valuable because many Building Regulations issues happen through the construction rather than across the plan.

A section through an extension can communicate the relationship between:

ground → foundation → floor → external wall → roof → existing house.

That makes it possible to understand junctions that cannot be adequately explained on a floor plan alone.

Construction Details

Some parts of a building benefit from enlarged technical details.

Examples might include:

• wall-to-floor junctions;

• wall-to-roof junctions;

• roof edges;

• openings;

• thresholds;

• interfaces with existing construction; and

• other project-specific junctions.

The purpose is not to fill a drawing sheet with standard details.

A useful detail should resolve something that actually matters to the proposed building.

Construction Specification

Drawings frequently work alongside written technical notes or specifications.

These can define proposed materials, construction principles and applicable performance requirements.

This is important because not every piece of technical information is best communicated graphically.

A good technical package therefore combines:

drawings + specifications + calculations + specialist information where required.

Structural Information

Architectural technical drawings do not replace structural engineering.

Where structural work is proposed, the project may require calculations and details prepared by a structural engineer.

Merton's current Full Plans guidance specifically identifies structural calculations for work such as loft conversions, removal of load-bearing walls and creation of structural openings.

That might include:

• beams;

• columns;

• lintels;

• structural alterations;

• roof modifications;

• foundations; or

• other engineered elements.

The architectural and structural information should then be coordinated.

A beam should not exist in one designer's calculation while colliding with a window, ceiling or drainage route on somebody else's drawing.

Drainage

Extensions frequently affect drainage.

A project may encounter:

• existing foul drains;

• surface-water drainage;

• inspection chambers;

• new bathrooms or utility rooms;

• rainwater disposal;

• public sewers; or

• drainage running beneath the proposed footprint.

That information should be investigated early enough to influence the design.

Drainage discovered only when excavation begins can become an expensive site problem.

Thermal Design

Alterations to the building envelope introduce thermal-performance requirements.

That can affect:

• new floors;

• external walls;

• roofs;

• windows;

• doors;

• rooflights;

• existing elements affected by the work; and

• overall energy-performance calculations where applicable.

This area has also changed recently.

The Government published new Approved Documents L and F on 24 March 2026 as part of the Future Homes and Buildings Standards changes, with earlier editions continuing to apply to buildings that remain subject to earlier regulatory standards.

That is a useful example of why technical specifications should be prepared against the regulatory requirements applicable to the actual project, rather than copied uncritically from an old drawing.

Ventilation

As buildings become more thermally controlled and airtight, ventilation needs to be designed rather than treated as an afterthought.

Depending on the work, the design may need to consider:

• background ventilation;

• extract ventilation;

• purge ventilation;

• kitchens;

• bathrooms;

• utility rooms; and

• ventilation implications of altered existing rooms.

The applicable strategy depends on the project and regulatory standard.

Fire Safety

Fire-safety requirements vary considerably depending upon the building and work proposed.

A simple single-storey extension presents different issues from a loft conversion that creates another storey.

Technical design may therefore need to address matters such as:

• escape;

• doors;

• protected routes;

• alarms;

• internal linings;

• structural fire resistance; and

• relationships between new and existing accommodation.

This is another reason not to treat Building Regulations drawings as a generic template.

This distinction is fundamental.

Building Control assesses regulatory compliance.

The designer remains responsible for the design within their scope.

Since October 2023, England's Building Regulations dutyholder regime has made those responsibilities much more explicit.

Government guidance states that designers must plan, manage and monitor their design work and take reasonable steps to ensure that the design, if built, complies with the relevant Building Regulations. Designers working on part of a project must also consider how their design interacts with other design work.

For domestic clients, where there is more than one designer or contractor, the regulations also establish Principal Designer and Principal Contractor arrangements; if the domestic client does not make those appointments, the designer and contractor in control can acquire those roles automatically.

So:

Building Control checks.
Designers design.
Engineers engineer.
Contractors build.

Those functions interact, but they are not interchangeable.

Not necessarily.

There can be considerable overlap, particularly on straightforward domestic work.

But the terms describe different objectives.

A Building Regulations package is principally developed to demonstrate and communicate regulatory compliance.

A comprehensive construction package may go further into matters such as:

• setting out;

• bespoke junctions;

• detailed schedules;

• finishes;

• manufacturer-specific requirements;

• coordination between trades; and

• information required for procurement and construction.

The appropriate level of information depends upon the project and the service commissioned.

Homeowners should therefore avoid assuming that the phrase “Building Regulations drawings” automatically means every drawing a builder could possibly require.

The scope should be defined.

A builder can only price what has been defined.

If three contractors receive only a planning drawing, they may make three different assumptions about:

• roof construction;

• floor construction;

• insulation;

• drainage;

• steelwork;

• glazing;

• openings; and

• other technical elements.

Their prices may therefore appear comparable when their assumptions are not.

Technical drawings cannot eliminate every uncertainty in an existing building.

But they can substantially reduce avoidable ambiguity.

That improves the basis for:

Building Control assessment → structural coordination → contractor pricing → construction.

This follows directly from yesterday's ADS article.

A Building Notice can allow eligible smaller projects to proceed without the same formal pre-construction plan approval provided by Full Plans. GOV.UK describes Building Notice as a route for smaller projects and confirms that it does not provide formal approval in the way Full Plans does.

But:

less information required for the application does not automatically mean less information required to design the building properly.

The builder still needs sufficient information.

Structural elements still require design.

Regulatory requirements still apply.

And the dutyholder responsibilities still apply.

That is why the decision about what technical information the project needs should not be reduced to the minimum paperwork required to lodge a Building Control application.

Ideally, establish:

1. What you are building

The architectural design should be sufficiently resolved.

2. The planning position

Planning permission, Permitted Development, Lawful Development Certificate or another route should be understood.

3. Existing construction

The designer needs reliable information about the building being altered.

4. Structural implications

Identify where structural engineering is likely to be required.

5. Drainage constraints

Especially where an extension is proposed over or close to existing drainage.

6. Building Control route

Decide whether Full Plans or another available route is appropriate.

Then the technical design can be developed around a coherent project rather than a collection of assumptions.

Do I need Building Regulations drawings for an extension?

Where a Full Plans application is being made, detailed technical information will normally form part of the submission. The precise drawings, specifications and calculations depend upon the extension.

Are planning drawings enough for my builder?

Sometimes they may show enough geometry to understand the concept, but they do not necessarily resolve the technical construction. For substantial work, relying on planning drawings alone can leave important matters to assumptions on site.

Does the structural engineer prepare all the Building Regulations drawings?

Normally not. The structural engineer typically deals with the structural design within their appointment. Architectural technical information covers the wider building design, and the two need coordination.

Does Building Control approve the builder?

No. Building Control's regulatory role should not be confused with appointing, supervising or warranting the contractor.

Can I reuse details from another extension?

Standard construction principles can be useful references, but the technical solution must suit the actual property, design and regulatory requirements. Existing ground conditions, drainage, structure, geometry and junctions can differ significantly.

Do drawings guarantee Building Regulations approval?

No professional drawing package should be described as a guarantee of approval. Building Control independently assesses the submission, may request additional information or amendments, and subsequently inspects relevant stages of construction.

Architectural Drawing Studio develops residential projects beyond the planning stage into coordinated technical Building Regulations information.

Depending upon the project, that can include proposed technical plans, sections, construction details, specifications and coordination with structural-engineering information.

The objective is not simply to produce more drawings.

It is to answer important construction questions before the builder has to answer them on site.