# Do I Need an Architect for My Extension — or Is There a Third Option?

> Do you need an architect for a house extension? When design + CA is essential, when DIY management works, and when a client-side PM is the third option — without skipping design.

Author: Ben Murrell, Homeowners Project Manager · Published: 2026-09-20 · Category: Project Management · Areas: South West London
Canonical: https://www.homeownersprojectmanager.co.uk/blog/architect-or-manage-your-build-yourself-third-option

You have planning approval, a set of drawings you love and a builder lined up. Now comes the question most homeowners do not think about until late: **who is actually going to run the job?**

Most people think there are two answers. You pay your architect to carry on through the build, or you manage it yourself and save the fee. Both can work. But there is a third option that often gets the best of both, and on the right project it pays for itself.

I project manage residential renovations and extensions across South West London. Here is how I would think about the choice — including the times when your architect really is the right person for the job.

## Option 1: Your architect manages the build

Many architects offer a service beyond design, often called contract administration. It covers the construction stage of the RIBA Plan of Work. They inspect the works, issue instructions to the builder, value the work done and certify payments.

**Where this works well:**

- **Complex or high-design projects.** If your scheme depends on precise detailing — frameless glazing, hidden structure, a bespoke staircase — the person who designed it is well placed to protect it.
- **Formal contracts.** On larger projects under a [JCT contract](https://www.homeownersprojectmanager.co.uk/blog/jct-contracts-explained-for-homeowners), a named contract administrator who understands the paperwork is valuable.
- **Listed buildings and conservation areas.** Where design decisions on site need to stay in line with consents, the architect’s continued involvement gives real peace of mind.
- **A strong existing relationship.** If you trust your architect, they are responsive and they know your builder, carrying on together is often the easiest path.

**The trade-offs:**

- **Cost.** Architects usually charge for the construction stage as a percentage of build cost or as a separate fee, and it is often a big part of the total.
- **Time on site.** Most architects run several projects at once and visit site at set intervals, often fortnightly. Problems on a build do not wait for the next visit.
- **Focus.** Their training and business are built around design. Many are excellent on site, but chasing deliveries, comparing supplier quotes and sorting the day-to-day problems between trades is not always where their time goes — and it is not always what they are paid for.

## Option 2: You manage it yourself

Plenty of homeowners take this on, usually to save money. On a small, simple project with a builder you trust, it can work.

**Where this works well:**

- Smaller, straightforward jobs such as a kitchen refit, a bathroom or redecoration.
- You have time during the working day to be on site and answer calls.
- You have some construction experience, or a builder you have used before and trust completely.

**The trade-offs:**

- **Reading the drawings.** Architectural and structural drawings are technical documents. Missing a detail — a set-down for flooring, a beam bearing — gets expensive once it is built in.
- **Decisions on the spot.** Builders will ask questions daily. “Do you want the sockets here or there?” is easy. “The steel won’t sit where the engineer’s drawn it — what do you want to do?” is not.
- **Buying power.** Homeowners usually pay retail for materials, or accept whatever the builder prices in, with no easy way to check whether it is fair.
- **Time and stress.** Managing a build is effectively a part-time job, on top of your real one, often while you are [living in the house](https://www.homeownersprojectmanager.co.uk/blog/living-in-your-house-during-a-renovation).

## Option 3: An independent project manager

This is the option many people do not know about. A project manager sits between you, your architect and your builder. Their only job is to get your project built to the design, on budget and with as few surprises as possible.

Here is what that looks like when I am running a job.

### I sort problems on site, directly with the builder

Every build hits problems. You open a wall and find something unexpected, a delivery does not turn up, or a detail does not work as drawn. I have spent years on residential sites, so I can talk to the builder in their own language, understand the practical options and agree a fix the same day. Small problems do not get the chance to become expensive delays.

### I understand the drawings and protect the vision

I read architectural and structural drawings, and my job is to make sure what gets built matches them. When something needs to change on site, I make sure the change still delivers what you and your architect set out to achieve — not just whatever is easiest for the builder.

### I find materials that do the same job for less

This is where I usually earn my fee. A specification often names a particular product because it is the one the designer knows, not because it is the only one that works. I can often suggest alternatives with the **same performance** — thermal, structural, fire or finish — for **as little as half the price**. Where the look really matters, we keep the specified item. Where nobody will ever see it, there is no reason to pay a premium. More on this in [how product knowledge saves money on a renovation](https://www.homeownersprojectmanager.co.uk/blog/how-product-knowledge-saves-money-on-a-renovation).

### I source materials and get competing quotes

I go to suppliers directly, get competing quotes and use [trade relationships](https://www.homeownersprojectmanager.co.uk/blog/why-industry-contacts-save-homeowners-money) to get prices you cannot get on your own. I also check builders’ quotes line by line so you know what you are paying for. **My aim is for the savings from suppliers to fully cover my fee — and to show you the figures.** You should not have to take that on trust; you will see where every saving came from. See [does a project manager’s fee pay for itself?](https://www.homeownersprojectmanager.co.uk/blog/does-a-project-manager-fee-pay-for-itself)

### Your project is my main focus

This matters more than people expect. An architect’s business is built around winning and delivering design work, and your build is one of several jobs competing for their time. Mine is built around running builds. When your project is on site, it gets my full attention: regular site visits, fast answers to the builder’s questions, and one person you can call who knows exactly where everything stands.

## The best option: a project manager working alongside your architect

This is not really a choice between architect and project manager. On most projects, **the best result comes from both working together**, each doing what they do best.

- **Your architect** owns the design. They answer design questions, sign off changes that affect the look and feel, and deal with planning and consents.
- **I own delivery.** I run the site day to day, manage the builder, source materials, control costs and keep the programme moving.

Your architect gets fewer phone calls about skip deliveries and missing fixings, and can spend their time on the decisions that need a designer. You get the design you paid for, delivered by someone whose full attention is on building it well. Often the combined cost is less than paying the architect for full contract administration — especially once supplier savings are counted. For how the two roles divide in more detail, see [client-side PM vs architect contract administration](https://www.homeownersprojectmanager.co.uk/blog/client-side-pm-vs-architect-contract-administration-sw-london).

## And the main contractor?

The builder is the fourth name in this conversation, and it is worth being clear about what they do and do not cover. A good main contractor manages their own trades, their own programme and their own margin — that is the job. But their commercial interest is in their own profitability, not in minimising your spend. That is not a criticism of builders; it is simply the structure of the relationship, and it is why it helps to have someone on the other side of the table who has no stake in it.

Most projects need an architect and a main contractor regardless. The genuinely optional role is the third one — and whether you need it comes down to how much time you have, how comfortable you are reading a construction quote line by line, and how much is riding on the budget.

## How to decide

As a rough guide:

- **Small, simple job, a builder you trust and time on your hands** — manage it yourself.
- **High-design, listed or complex scheme, with an architect keen to stay involved on site** — your architect, ideally with a project manager handling the day-to-day running.
- **Extension, loft or full renovation with approved drawings, and you want cost control and someone on site regularly** — an independent project manager, working with your architect where needed.
- **Not sure how well your architect and builder will work together** — a project manager as the link between them.

The size of the project matters, but so does the relationship. If you and your architect work well together and they are keen to stay involved, that is a real asset — and a project manager can work alongside them rather than replace them. If their involvement is winding down after planning, or the construction fee is more than you had planned for, a project manager fills the gap without losing the vision.

## Talk it through

If you are in South West London and weighing up how to run your build, I am happy to look at your drawings and talk through the options — including whether you need me at all. For some projects the honest answer is that your architect or a good builder has it covered. For many others, the savings alone make the case. [Get in touch](https://www.homeownersprojectmanager.co.uk/contact).

Related: [client-side PM vs architect contract administration](https://www.homeownersprojectmanager.co.uk/blog/client-side-pm-vs-architect-contract-administration-sw-london) and [what a project manager costs](https://www.homeownersprojectmanager.co.uk/project-manager-cost).

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Homeowners Project Manager — independent client-side project management for homeowners in South West London. Contact: 07525 474 849 · https://www.homeownersprojectmanager.co.uk/contact