Design and Build vs Using a Separate Architect and Builder for a House Extension in Essex

A design and build company in Essex looks after the drawings, planning application, structural engineering and builder introduction as one service, whereas with a separate architect you coordinate each stage yourself and only appoint a builder once planning is approved.

Neither route is automatically better. Design and build suits most standard house extensions, loft conversions and side extensions, while a separate architect can make more sense for listed buildings or highly ambitious one-off designs. This guide compares the two on process, cost and risk, so you can decide which fits your project.

We are Kirkwood, a design company working across Essex, so we do have a view. We use our own model as an example of design and build done well, but we will be straight about when it isn’t the right fit.

Contents

What does a design and build company actually do?

A design and build service takes your project from first idea to a buildable scheme under one roof. In practice, one company handles:

The initial design consultation
The architectural drawings
The planning application, or a Lawful Development Certificate where the project falls under permitted development
Structural engineering
Building Regulations drawings
An introduction to a vetted builder

You deal with one team throughout. When you need an answer, there is one place to ask, rather than three companies passing the question between them.

Design and build is not one fixed model, though. Some companies are design-led, and some are builders with a designer in-house, so it is worth asking where a company’s strength lies and who is responsible for each stage.

Here is how that works at Kirkwood. When a client comes to us, it starts with a free Discovery Call. Our design team then prepares the design, and we handle planning permission on your behalf. Our structural engineering is done in-house, and we produce the Building Regulations drawings. We then introduce a builder we have worked with, and we support you and the builder through the build.

What does the traditional route (separate architect and builder) involve?

On the traditional route, you appoint each professional yourself. It usually runs like this:

You appoint an architect to produce the drawings and handle the planning application.
You appoint a structural engineer, usually as a separate appointment.
Once planning is approved, you put the build out to tender with several builders and compare their quotations.
You appoint the builder you choose and manage that relationship.

That makes you the coordinator. You pass information between the architect, the engineer and the builder, chase answers and spot any gaps between what each of them has done.

That is not a criticism. For large, complex or very individual projects that call for specialist architectural input, this route can work very well, and it gives you direct control over every design decision. The trade-off is your time and effort, and the fact that you are the one holding the pieces together.

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Design and build vs separate architect — a side-by-side comparison

Here is how the two routes compare at a glance.

	Design and build (e.g. Kirkwood)	Separate architect + builder
Single point of contact	Yes — one team through the design stages and into the build	No — architect, structural engineer and builder are separate appointments
Cost transparency	Professional fees usually agreed upfront	Costs can escalate as separate quotes come in
Planning and drawings	Handled in-house	Architect handles them; you coordinate
Builder relationship	Company introduces a vetted builder	You find and appoint the builder separately
Risk if something goes wrong	One company is responsible for design and specification	Responsibility can be disputed between parties
Flexibility / one-off design	Good for most home extensions	Better for highly complex or unique projects
Timeline	Streamlined — no handoff gaps between stages	Can be slower because of coordination between parties
Typical cost	Professional fees agreed upfront; build cost depends on the builder’s quote.	Architect’s fees often 5–15% of build cost, plus separate engineering and Building Regulations fees; build cost varies by builder

Treat the table as a general guide rather than a rule. A well-run traditional project can be smooth, and a badly run design and build project can still go wrong, so the company you choose matters as much as the route.

Cost comparison — is design and build cheaper?

Not automatically. Design and build is more cost-certain, which is a different thing from cheaper.

With design and build, you know what you are paying for the professional side before work starts. At Kirkwood, architectural design, structural engineering and Building Regulations are charged as separate items, so you can see what each one costs. On one of our Chelmsford projects, the total professional fees came to £4,935. That is one example rather than a typical price, because every project differs.

On the traditional route, an architect’s fees typically run at 5–15% of the build cost. The structural engineer’s and Building Regulations fees then come on top, and the builder quotations that follow can vary significantly. Because the architect’s fee rises with the build cost and the builder’s price isn’t known until after planning, the final total is harder to predict at the start.

So which is cheaper? It depends on the builder you end up with and how tightly the project is controlled. A traditional project can come in lower if you tender well, or higher if the scheme grows or the quotes surprise you. Design and build gives up some of that variation in exchange for certainty, with the design shaped around a realistic budget from the outset.

Remember too that professional fees are only part of the budget. The build itself is the bigger figure, so ask for realistic build cost guidance early, before the design is fixed.

Whichever route you take, compare like for like and get the scope of every fee in writing. Our guide to the questions to ask before appointing a design company covers what to check.

Which route is right for your project?

Design and build usually works best for

Standard house extensions
Kitchen extensions
Loft conversions
Side extensions
Most projects up to around £200,000 build cost

These are well-trodden projects with predictable planning and structural requirements, so the benefits of one team are strongest: fewer handoffs, clearer costs and a smoother path to site.

A separate architect may suit you better if

Your building is listed and needs specialist knowledge
The project is highly individual or architecturally ambitious
It is a commercial development

Kirkwood doesn’t suit every project, and neither does any other design company. If you are planning something at that end of the scale, a specialist architect is likely to serve you better, and it is better to know that before you commit to anyone.

The £200,000 figure is a rule of thumb rather than a cut-off. A simple project above it can still suit design and build, and a small but unusual one may not.

If your project sits between the two, ask yourself how much control you want over every design decision, and how much time you can realistically spend coordinating.

The design and build process at Kirkwood Build

This is the sequence we follow when a client chooses design and build with us:

Free Discovery Call. We talk through your property and what you want to achieve, and look at which planning route is likely to apply. You can book a free Discovery Call online.
Design. Our design team prepares the design and drawings.
Planning. We prepare and submit the planning application, or a Lawful Development Certificate where the project falls under permitted development.
Structural engineering. The structural calculations are produced in-house, alongside the design.
Building Regulations. We produce the technical drawings your builder and building control will work from.
Builder introduction. We introduce a vetted builder we have worked with. You should still compare proper quotations before you commit.
Support through the build. We continue to support you and your builder while the work is under way.

For a sense of how long each stage takes, see our guide to how long a house extension takes.

What to look for in a design and build company in Essex

When you are comparing design and build Essex companies, whether Kirkwood or anyone else, these are the points that separate a good one from a poor one:

Who does the structural engineering. Is it done in-house, or passed to another company?
What the fee includes. Ask for the scope in writing, covering drawings, planning, engineering and Building Regulations.
Whether you can speak to previous customers, ideally in your area with a similar project.
Local planning knowledge. Essex has several planning authorities, including Chelmsford City Council, Brentwood Borough Council and Basildon Council, and experience of the one covering your home helps.
Honesty about planning. Nobody can guarantee permission, so be wary of anyone who says they can.
Where the service ends. Find out who deals with problems during the build, and who you speak to.

Project details at a glance — what Kirkwood handles end to end

Initial design consultation through a free Discovery Call
Architectural drawings
Planning permission, or a Lawful Development Certificate where permitted development applies.
Structural engineering, in-house
Building Regulations drawings
Introduction to a vetted builder
Support for you and your builder through the build

Not sure which route suits your house extension? Book a free Discovery Call and the Kirkwood team will tell you honestly whether design and build is the right fit, or whether you would be better served elsewhere.

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No, you don’t need a registered professional carrying that specific title for a house extension. What you do need is proper planning drawings, structural engineering, and building regulations drawings, and Kirkwood produces all three in-house for extensions across Chelmsford, Brentwood, Billericay, Wickford, Basildon, Rayleigh, Leigh-on-Sea, Southend, and the surrounding areas of Essex.

Frequently Asked Questions

Is design and build cheaper than using a separate architect in Essex?

Not by default, but it is usually easier to predict. With design and build, you know the professional fees before work starts. The traditional route typically means architect’s fees of 5–15% of build cost, separate engineering and Building Regulations fees, and builder quotations that can differ widely. What you pay overall depends on the builder you choose.

Does a design and build company do the architectural drawings?

Yes. The drawings are where our service starts. After a free Discovery Call, the Kirkwood design team prepares the design and drawings, which then feed into the planning application, structural engineering and Building Regulations stages.

What happens if something goes wrong with a design and build company?

You have one company to go back to for the design and specification, rather than waiting for several parties to agree whose job it was. Once the build is under way, Kirkwood stays involved with you and the builder, and can review the design or structural information if something unexpected turns up.

Do I still need planning permission with a design and build company?

Yes, the rules are the same whichever route you use. The difference is that the design and build company handles the process for you. Some extensions fall under permitted development and may only need a Lawful Development Certificate, while others need a full householder application. Our guide to permitted development vs planning permission explains how to tell which applies.

Can Kirkwood Build cover my area of Essex?

Yes. Kirkwood works across Essex, including Chelmsford, Billericay, Wickford and Leigh-on-Sea, and Brentwood (see our Brentwood architects page), along with the surrounding towns. If you are not sure whether your address is covered, mention it on your Discovery Call.

Explore our Services

Architectural Design

Designing Extensions That Suit Your Budget

Council Permissions

Help You Get Approval For Your Project

Structural Engineering

Complete Structural Engineering Service

Kitchen Extension Design

A kitchen is the heart of a home

Single Storey Design

Bespoke designs tailored to your needs

Double Storey Design

Let Us Help Maximise Space And Create More Comfort

Loft Conversion Design

Turn Your Loft Into Family Living Space

Garage Conversion Design

Changing Your Garage Into Extra Living Space

Jamie Lindsay is the founder of Kirkwood Build and has over 15 years of experience in residential construction, architectural design, and home extensions across Essex. He specialises in helping homeowners navigate the design, planning, and building process, sharing expert advice on extensions, renovations, and property improvements through the Kirkwood Build blog.