DO WE NEED DETAILED DESIGN DRAWINGS AND BUILDING REGULATIONS DRAWINGS?

Quick summary

For most home extension, conversion, and refurbishment projects, planning drawings alone are not enough to build from. Detailed design and Building Regulations drawings help avoid confusion on site, allow builders to price accurately, ensure legal compliance, and are usually required to achieve Building Regulations completion at the end of the project.

Planning approval is a major milestone, and it is completely understandable that many clients ask whether they really need to do any more drawings once permission is granted. It is also common for builders to say they can work straight from the planning set.

In our experience, for the vast majority of domestic projects, proceeding without a detailed design stage creates unnecessary risk and uncertainty. This guide explains why we normally recommend continuing beyond planning, what the detailed design stage actually does, and the limited situations where it may be reasonable not to.

WHAT PLANNING DRAWINGS ARE FOR

Planning drawings are produced to secure planning permission. Their role is to demonstrate scale, appearance, layout, and impact.

They are not intended to show:

• How the building will be constructed

• How structural, thermal, fire, or moisture requirements will be met

• Detailed levels, junctions, or interfaces

• The quality or performance standard you may be expecting

This is entirely normal. Planning drawings are doing exactly what they are meant to do.

WHAT DETAILED DESIGN AND BUILDING REGULATIONS DRAWINGS DO

Detailed design drawings take the approved planning scheme and turn it into something that can be properly built, checked, and signed off.

They typically include:

• Wall, roof, and floor build ups

• Structural coordination

• Insulation, fire safety, and moisture control detailing

• Drainage, ventilation, and services strategy

• Key dimensions, setting out information, and levels

• Quality and workmanship control

These drawings are usually submitted to Building Control as part of a Full Plans application and form the technical backbone of the project.

WHY THIS STAGE IS USUALLY WORTH IT

Reducing decisions made under pressure

Without a detailed design stage, many important decisions are pushed into the construction phase. That usually means decisions are made quickly, on site, often without the chance to properly consider cost, alternatives, or long-term implications.

Some site decisions are inevitable, but a completed design greatly reduces how many there are.

Clearer expectations between client and builder

One of the biggest sources of tension on projects is differing assumptions.

Clients may believe they are getting one level of specification, performance, or finish, while the builder is assuming something else entirely. Without detailed drawings or specifications, there is often no clear record of what was actually agreed.

A proper drawing set creates a shared reference point and helps protect both sides.

More accurate pricing and fewer surprises

Builders can only price what they can see. Where information is missing, assumptions have to be made.

Detailed drawings:

• Reduce ambiguity

• Allow quotes to be compared more fairly

• Lower the likelihood of variations and additional costs later

In many cases, the cost of the drawings is small compared to the financial uncertainty they help avoid.

A robust route through Building Regulations

For most projects, Building Regulations approval is required. There are two routes: Building Notice or Full Plans.

For anything beyond very minor work, we strongly recommend Full Plans. This requires a developed set of drawings so compliance can be checked before work starts, rather than relying entirely on site inspections and late changes.

THE COMPLETION CERTIFICATE, AND WHY THIS MATTERS

This is often the most important and least understood part of the process.

At the end of a project, Building Regulations completion is confirmed by issuing a completion certificate. This certificate is increasingly important for future sale, remortgaging, and legal compliance.

That certificate requires confirmation from:

• The client

• The Principal Designer

• The Principal Contractor

If we complete the detailed design stage, we are able to act as Principal Designer for the design phase and sign off the relevant documentation.

If the detailed design stage is not undertaken, we cannot sign this paperwork. At that point, responsibility for completing the design and acting as Principal Designer passes elsewhere, often unknowingly. This typically falls to the builder, or in some cases the client, neither of which is normally appropriate or understood at the outset.

This is where many projects encounter problems late on, even if the build itself has gone reasonably well.

WHEN MIGHT IT BE ACCEPTABLE NOT TO PROCEED?

There are limited situations where stopping after planning may be reasonable. This is usually where:

• The work is genuinely simple and low risk

• The builder is already appointed and well known to the client

• The builder is experienced in completing design work and managing Building Regulations

• Everyone is clear, in writing, who is taking on the Principal Designer role

• The client is comfortable relying on site decisions rather than drawings

Even in these cases, we would always recommend confirming responsibilities clearly before work starts.

OUR RECOMMENDED APPROACH

For most domestic projects, we recommend completing a proportionate detailed design and Building Regulations package. This does not mean overcomplicating things. It means removing uncertainty, clarifying responsibility, and giving everyone a solid technical baseline to work from.

In practical terms, it leads to:

• Better pricing

• Fewer surprises

• Clearer accountability

• A smoother route to Building Regulations completion

FINAL THOUGHTS

If you are being told that planning drawings are enough, it is worth asking what is being relied on instead. In most cases, the missing information does not disappear. It is simply dealt with later, under more pressure, with less clarity, and often at greater cost.

If you would like to talk through what level of drawings is appropriate for your project, or understand what responsibilities would sit where if you chose not to proceed, we are always happy to have that conversation.

This article is provided as general guidance only and does not constitute legal or professional advice. Always seek tailored advice specific to your project or situation.