Design & Build vs Architect-Led: London Renovation Routes Compared (2026)

You've decided to renovate. Now you have to decide who you're actually going to hire, and that single choice will shape your budget, your timeline, and how many sleepless nights you have between now and handover.

Most London homeowners researching a £50,000 to £200,000 renovation discover there are roughly four ways to get the work done: hire a design-and-build firm that handles everything, appoint an architect and tender the drawings to a separate contractor, bring in a project management firm to coordinate trades you've hired separately, or run the job yourself by booking each trade direct. Each route has a place, a cost, and a different person holding the risk. This article walks through all four honestly.

The four ways to deliver a London renovation

People use these labels loosely, and a "design and build" firm in one quote can mean something different from the same label on another. The distinctions below are how the industry uses the terms when contracts get drawn up.

1. Design and build

One company designs your project, prices it, builds it, and signs it off with Building Control. You sign a single contract. One project manager runs the job from first survey to snagging list. The firm carries trades in-house or has long-standing subcontractors they manage directly. Drawings are produced by an in-house designer or a retained architect. The price is fixed before work starts, with a separate provisional sum for variable items you've agreed (kitchen, tiles, specialist finishes).

On cost, design-and-build sits in a useful middle ground. Design fees are typically rolled into the build price rather than billed separately. Contingency expectations are 5% to 10% of contract value for a renovation without major structural unknowns, and 10% to 15% if you're opening up a Victorian rear addition where the brickwork and drainage are anyone's guess until the plaster comes off. The hidden cost most people miss is variation pricing: if you change the spec mid-build, the firm prices the change as a one-off, and that price can carry a healthy margin. Lock the spec down before contract and this stops being an issue.

The risk position is the part most homeowners don't appreciate until something goes wrong. With design-and-build, the contractor carries buildability risk. If the design doesn't work on site, that's their problem to redesign and reprice, not yours to pay for. Timeline is usually 8 to 20 weeks for a standard rear extension and kitchen, 16 to 30 weeks for a full house renovation, assuming Building Control is straightforward.

2. Architect-led with separate contractor

An architect (RIBA Chartered, ideally) produces the design through RIBA Plan of Work stages 1 to 4, then you go to tender. Three or four contractors price the same drawings, you pick one, and the architect can stay on through construction (stages 5 to 6) to administer the contract on your behalf. Serious architectural projects have followed this route for decades and it produces the best design outcomes on paper.

It's the most expensive route by some distance. Architect fees on a residential renovation typically run 8% to 12% of build cost for full service (design through to contract administration), or 5% to 7% if you only want them to take you to planning and tender. On a £120,000 build, that's £6,000 to £14,400 in design fees alone. Structural engineer fees sit on top, usually £1,500 to £4,000. The build itself, tendered competitively, often comes in 5% to 15% higher than a design-and-build equivalent because the contractor is pricing a fixed scope with no flex and adds risk margin for anything the drawings don't fully specify.

Risk is split. The architect carries professional indemnity on the design. The contractor carries the build risk. You sit in the middle holding two contracts, and if a problem on site is caused by an ambiguous drawing, you can end up watching the architect and contractor argue about whose fault it is while you pay for both their time. A good architect administering the contract well prevents this. A disengaged one does not. Timeline is typically 6 to 9 months longer than design-and-build, because design through planning to tender to start on site is rarely under four months.

What you get for the extra money is design quality and independent oversight. For complex sites, listed buildings, or anywhere the architecture is genuinely the point, this route earns its keep.

3. Project management firm

A project manager (or PM firm) coordinates trades on your behalf. You hold the contracts with each trade. The PM schedules them, checks the work, handles materials procurement, and reports to you. Fees are typically 8% to 15% of build cost, or a fixed monthly retainer. PMs come from quantity surveying, construction management, or site management backgrounds.

The cost looks attractive on paper because there's no main contractor margin on labour and materials. You pay trade rates direct plus the PM's fee. On a £100,000 renovation that might be £8,000 to £15,000 in PM fees rather than the £15,000 to £25,000 a main contractor would build in. Savings only materialise if the PM runs a tight ship. Delays, reordered materials, trades down-tooling because a previous trade overran, all land on your bill rather than being absorbed by a fixed-price contractor.

The risk position surprises homeowners. You are the legal client of every trade. If the electrician's work fails Building Control, you chase the electrician. If the plumber damages the new floor the joiner just laid, you mediate. If a trade goes bust mid-job, you find another one and pay them again. The PM advises and coordinates, but the contracts are yours. Many PMs are excellent and homeowners with the temperament for this route swear by it. Others regret it once the third change of trade has cost them six weeks and £8,000 they didn't budget for.

Timeline depends entirely on the PM's diary and how well they sequence trades. A well-run PM-coordinated job can match a design-and-build timeline. A poorly run one drifts indefinitely.

4. Direct trades hire

You become the project manager. You find a builder, electrician, plumber, plasterer, kitchen fitter, tiler, decorator. You sequence them, order materials, sign off the work, and apply for Building Control yourself (or your builder does on the small parts they're responsible for).

This route can produce the lowest headline cost because you've stripped out every layer of management. On a kitchen refurbishment, a small bathroom job, or a single-trade replacement (rewire, boiler swap), it's often the right answer. People save thousands going direct on jobs of that size.

On anything bigger, the cost picture changes. Savings get eaten by the things you didn't know to plan for. Skip hire booked on the wrong day. Electrician arriving before the chasing is finished. Steel beam arriving on a Friday with nobody on site to receive it. Each of these costs money and time. The honest version of this route is that it works brilliantly for homeowners who have done it before, have flexible time during the working week, and have a good gut for spotting when a trade is winging it. For first-timers on a £100,000-plus renovation, the saving rarely survives contact with reality.

Risk is entirely yours. If a trade does work that fails Building Control, you pay to redo it. If two trades disagree about who damaged what, you decide. If a trade walks off mid-job, you find a replacement. There is no contract to lean on beyond what you've put in writing, and most trades work off a quote, not a contract. Direct-hire jobs realistically run 30% to 50% longer than the same scope under a main contractor, because nobody is paid to keep the programme on track.

Side-by-side comparison

Factor	Design and build	Architect-led	PM firm	Direct trades
Total cost predictability	High (fixed price, defined variations)	Medium (tendered fixed price, but design fees and variations can add up)	Low to medium (depends on PM and trade reliability)	Low (you absorb every overrun)
Single point of contact	Yes — one PM, one contract	No — architect and contractor, sometimes structural engineer too	One PM, but multiple trade contracts	None — you are the contact
Design quality ceiling	Good to very good for standard residential work	Highest — bespoke architectural design	Depends on who you appoint to design	Depends on what you draw or commission
Risk allocation	Contractor carries buildability and trade risk	Split between architect (design) and contractor (build)	Homeowner carries trade risk; PM carries coordination risk	Homeowner carries everything
Typical timeline (mid-size reno)	4 to 8 months end to end	10 to 16 months end to end	6 to 12 months end to end	8 to 18 months end to end
Best for	One number, one team, predictable handover	Architecturally ambitious projects, listed buildings, complex sites	Construction-literate homeowners with time to engage	Small jobs, single-trade work, experienced self-managers
Watch-outs	Lock the spec before contract; variations cost more later	Design fees plus build can stretch the budget; pick an architect who actually administers the contract	Check PM references on troubled jobs, not just smooth ones	Be realistic about your time and tolerance for problems

Which route is right for you?

It depends on the project, your appetite for involvement, and how much design ambition is driving the brief. Here's how the choice usually breaks down at three project sizes.

Small extensions (£30,000 to £60,000)

At this size, the maths almost always favours design-and-build, or direct hire for single-trade-heavy jobs. The fixed costs of an architect-led process (design fees, tender period, contract administration) eat too much of a small budget. A loft conversion, a single-storey rear extension under 20 square metres, a full bathroom refit. These are bread-and-butter design-and-build work, and cost certainty is worth more than a bespoke design that's constrained by the existing house geometry anyway.

If you want something visually distinctive, you can still get a small project from an architect, but expect design fees of £4,000 to £7,000 on top of the build. On a £40,000 job, that's a significant share of budget going to drawings. For most homeowners at this scale, our kitchen extension route through a single contractor produces a better cost-to-quality outcome.

Mid-range renovations (£80,000 to £130,000)

This is the bracket where the choice gets genuinely interesting. Design-and-build is the most popular route at this size for good reason: fixed price, single contact, defined timeline. But this is also where a good architect can add real value, particularly if you're doing a full house refurbishment or working with a property that has unusual constraints (split levels, awkward staircase, side return that needs careful daylight modelling).

The decision comes down to this: how much does the design matter, and how much risk are you willing to absorb? If the answer is "I want a beautiful, considered design and I'm comfortable holding two contracts," go architect-led. If the answer is "I want a good design, delivered on time, with one team responsible for everything," go design-and-build. Both are legitimate. We see homeowners in Clapham, Battersea, Dulwich, and Greenwich split roughly down the middle at this budget.

Project management is a fair shout at this budget too, but only if you're personally engaged enough to be on email with the PM most days and on site at least weekly. Direct hire at this scale is doable but high-risk for first-timers.

Large or listed projects (£150,000 and above)

For a major structural job, a listed building, or anything where conservation officers are involved, architect-led is usually the right route. A conservation architect understands the heritage consenting process, knows which materials and methods will be accepted, and can negotiate with the local authority in a way that contractors generally can't. Running a Grade II listed renovation through a standard design-and-build firm is a recipe for delays and rejected applications.

The same applies to projects with serious structural complexity: full basement digs, major remodelling that changes the load path through the house, anything where the structural engineer's drawings will be referenced weekly on site. The independent oversight of an architect administering the contract pays for itself in problems caught early.

Design-and-build still has a place at this size on non-listed properties with conventional structural ambitions. A £180,000 full house renovation with a rear extension and loft conversion in a standard Victorian terrace sits comfortably in design-and-build territory if the contractor is properly accredited and has the team for it. Above £250,000, or on any property with planning sensitivities, architect-led is usually safer. Where design-and-build is the right call, our bathroom fitting and full-house renovation services cover most South London project types.

How All Well runs design-and-build projects

All Well is a design-and-build contractor based at Unit 1 Limes Avenue, Anerley SE20 8QR. Companies House 12721034. Founded by director Richard Pryce in 2020, with 57 verified Google reviews averaging 4.5 out of 5 at the time of writing.

The model is straightforward. One survey, one detailed quote, one fixed-price contract with defined provisional sums for client-selected items (kitchen, tiles, sanitaryware, flooring). One project manager from first visit to snagging list. The contract includes Building Control sign-off, structural engineer drawings where required, and all trade certifications: NICEIC for Part P electrical works, Gas Safe for boiler and gas works, FENSA for windows and doors, CHAS for site safety and contractor competence.

Fixed-price discipline matters because cost-plus contracts (where you pay actual cost plus a percentage margin) are how renovations end up 30% over the original quote. Pricing is locked at contract, with variations priced as separate written instructions before the work proceeds. If we've underestimated something that's our cost to absorb, not yours to pay.

We cover 25 South East and South West London boroughs from the SE20 base, with most projects within a 45-minute drive: Bromley, Lewisham, Southwark, Lambeth, Wandsworth, Croydon, Greenwich. Project sizes run from £40,000 single-room renovations to £250,000 full house refurbishments with extensions. For full house projects, see property renovation; for extension and remodelling work, our kitchen extensions page covers the rear addition route most South London homes take.

Frequently asked questions

Is design-and-build cheaper than architect-led?

Usually, yes, but not always, and the saving isn't the main reason to pick it. On a £100,000 renovation, design-and-build typically lands 10% to 20% cheaper end-to-end once you account for architect fees, structural engineer fees, contract administration, and the margin contractors add when pricing tendered jobs with no flex. The bigger advantage is cost certainty and a single point of accountability. Architect-led can come out ahead financially where design choices unlock real savings (smaller footprint that still works, smarter structural solution, materials specified to avoid waste).

Can I use an architect AND a design-and-build firm?

Yes, and this is more common than people realise. You can engage an architect to take you through stages 1 to 3 (concept and planning), then bring in a design-and-build firm for technical design, building regulations, and construction (stages 4 to 6). You get the architect's design quality on the parts that matter most, with the cost certainty and single-team delivery of design-and-build. Some architects prefer to administer the contract themselves, but plenty work this way happily on smaller projects where a full RIBA service would be disproportionate to the budget.

How do design-and-build firms make money, and do I lose design quality?

Design-and-build firms make money on the build margin, the same way any contractor does. Design work is usually carried within that margin rather than billed separately, which is why the headline cost can look lower. Whether you lose design quality depends on who you hire. A firm with an in-house designer or retained architect can produce work as good as most independent architects on standard residential renovations. Where it falls short is on architecturally ambitious projects: listed buildings, contemporary new builds, design-led extensions where the architecture is the point. On a conventional rear extension and kitchen, the design quality gap is smaller than the marketing on either side suggests.

What if I already have architect drawings? Can a design-and-build firm take them on?

Yes. Most design-and-build firms will price and build to existing architect drawings, either as a tender alongside other contractors or as a direct appointment. You lose the design-side cost saving (you've already paid for it), but you keep the single-contract, single-PM build advantage. The firm will review the drawings for buildability and may suggest tweaks before signing. Accept these conversations: a buildability flag at quote stage is much cheaper than the same problem caught on site. If you want the architect to stay on for contract administration, agree that upfront so the contract structure is clear.

How do I check a design-and-build firm is qualified?

Start with the trade accreditations. For electrical work, you want NICEIC or NAPIT registration (covers Part P compliance). For gas and boiler work, Gas Safe is non-negotiable. Check the register directly at gassaferegister.co.uk rather than trusting a logo on a website. FENSA or Certass for windows and doors. CHAS for site safety and contractor competence. Beyond accreditations, check Companies House for years trading and confirmed director, ask for two or three recent references you can call directly, and look for verified Google review counts. Be cautious of firms that won't share recent client references on request.

What's the typical contract structure?

For residential design-and-build, the most common contract is a JCT Minor Works or Home Owner Contract, sometimes a bespoke contract drawn up by the contractor that mirrors JCT terms. It should define: total contract sum, provisional sums, stage payment schedule tied to defined milestones (not weekly), contract programme with start and target completion dates, variation procedure, retention (usually 2.5% to 5% held until snagging is complete), and defects liability period (typically 6 to 12 months after handover). If a contractor pushes back on written contract terms or wants cash without a contract, walk away.

Get a free quote

If you want a fixed-price design-and-build quote to compare against, we'll deliver a written quote within 7 to 10 days of the initial survey, with clear scope and provisional sums broken out separately. Visit our contact page to book a survey, or call 020 3920 9617 to speak to Richard direct. We work across Bromley, Lewisham, Southwark, Lambeth, Wandsworth, Croydon and the surrounding boroughs from our Anerley office. If your project is better suited to an architect-led route, we'll tell you.