By My Trusted Builder  |  Published June 2025  |  London  |  8 min read

Working With My Trusted Builder: How We Collaborate With Architects From RIBA Stage 3 to Handover

Most London architects have a contractor problem. Not a shortage of contractors — quite the opposite. The challenge is finding a main contractor who will join the project at the right moment, price it accurately, build it to drawing, keep the client informed without undermining the architect, and hand it over without a snagging list that runs to three pages. That combination is rarer than it should be.

This article explains exactly how My Trusted Builder (MTB) works alongside architectural practices on residential projects across London — from initial contractor engagement at RIBA Stage 3 through to practical completion and the end of the defects liability period. If you are an architect or practice principal evaluating whether MTB is the right contractor for a specific project or for ongoing collaboration, what follows is a transparent, stage-by-stage account of our process.

The Contractor Problem Architects Face in London

The failure mode architects encounter most frequently with main contractors falls into one of four patterns. First, the contractor prices low to win and then claims variations from the moment groundworks begin. Second, the contractor treats the employer's requirements as a rough guide rather than a contractual obligation, and design intent erodes week by week on site. Third, the contractor communicates directly with the client on matters of scope or cost, destabilising the architect's relationship with their own client. Fourth, the contractor does not understand contract administration and views every RFI or instruction as an opportunity to raise a day-work claim.

These are not problems unique to small or inexperienced contractors. They appear across the market. The common cause is that the contractor was never genuinely embedded in the design process, never fully understood what was being built, and was therefore always operating reactively. The fix is earlier, more structured contractor engagement — and a contractor who understands RIBA stages, JCT obligations, and the architect's position within the project.

MTB was built for that model. Our director, Alexandr Vreme, has over 20 years in construction and quantity surveying on London projects. We understand the difference between a Contractor's Design Portion and a full design-and-build appointment. We understand why the architect is the contract administrator under a JCT Standard Building Contract and what that means for the information release schedule. We understand that the architect's reputation is tied to every project we build together — and we treat it accordingly.

RIBA Stage 3: Where the Right Contractor Engagement Begins

RIBA Stage 3 (Spatial Coordination) is the earliest point at which it makes sense to bring a main contractor into conversation on most residential projects in London. At this stage the design is sufficiently developed for a contractor to identify buildability issues, flag procurement lead times on specialist subcontractor packages, and contribute to a realistic cost plan.

MTB offers a Pre-Construction Services Agreement (PCSA) for practices who want structured early contractor involvement without committing to a construction contract. Under a PCSA, MTB provides:

• A Stage 3 cost plan produced by our in-house quantity surveyor, referenced to the current design and aligned with the employer's budget
• Buildability review and written commentary on coordination risks between structural, mechanical, and architectural packages
• Subcontractor market intelligence — lead times, availability, and indicative package costs for specialist trades (bespoke joinery, structural glazing, wet rooms, M&E)
• Input on procurement strategy, including whether a single-stage or two-stage tender approach is appropriate for the project

This early involvement reduces the risk of a Stage 4 cost plan that does not reflect the market, and it gives the architect a realistic basis on which to advise the client before detailed design expenditure is committed.

Early engagement does not lock the client into MTB for construction. If the architect's procurement strategy requires a competitive tender at Stage 4 or 5, we price competitively alongside other contractors. Our PCSA work is priced transparently and does not create a conflict of interest in any subsequent tender process.

RIBA Stage 4: Tendering, Value Engineering, and the Contractor's Design Portion

Stage 4 (Technical Design) is where most residential projects in London go to tender. MTB prices from a properly coordinated tender package: drawings, specification, and, where possible, a bill of quantities prepared by our QS. We do not price from sketch drawings and we will tell an architect or client if a tender package is insufficiently detailed for an accurate fixed price — doing so protects everyone.

Two-Stage Tender

For larger projects — typically those above £300,000 in construction value — a two-stage tender is often the better procurement route. In the first stage, MTB is selected on the basis of preliminaries, overheads, and margin. In the second stage, we work open-book with the architect to build up subcontractor package prices against a fully coordinated design. The result is greater cost certainty and a contractor who understands the project thoroughly before a spade enters the ground. MTB is experienced in two-stage procurement and can advise on whether it is appropriate for a given project.

Value Engineering

Where a first-stage cost plan or tender return exceeds the client's budget, MTB provides structured value engineering — written options, with cost implications, that preserve design intent while reducing construction cost. We do not produce a list of material downgrades and present it as value engineering. We work through the design with the architect to identify where cost can be reduced without compromising the spatial, material, or performance ambitions of the scheme. Our recommendations are documented and require architect sign-off before they are incorporated.

Contractor's Design Portion (CDP)

Many residential projects in London include elements where the contractor carries design liability — structural steelwork connections, M&E coordination, specialist glazing, or bespoke joinery packages. Under a JCT contract incorporating a Contractor's Design Portion, MTB manages and integrates CDP elements without displacing the architect's overall design authority. We appoint specialist designers, obtain architect review of CDP submissions, and maintain a clear audit trail of design approvals. The architect remains in control of the project's aesthetic and technical coherence.

RIBA Stage 5: Construction — On Programme, On Budget, to Drawing

Construction delivery (RIBA Stage 5) is where commitments made at tender are tested. MTB's approach to Stage 5 is structured around three principles that are directly relevant to architects.

1. The information release schedule is a contract document

MTB produces and agrees an information release schedule at the start of every project. If the design team is running behind on a drawing issue, we raise it in writing through the RFI process — we do not stop work and we do not claim delay without first issuing a proper notice under the contract. Equally, if a late instruction from the architect causes a variation, we price it formally and obtain written approval before proceeding. There are no surprise claims at practical completion.

2. Site visits are collaborative, not adversarial

MTB welcomes architect site inspections. Our site managers brief visiting architects on programme status, current works, and any open design queries. We maintain a live RFI and variation log that the architect can request at any time. We do not communicate directly with the client on matters of scope, design, or cost without the architect's knowledge — all such communications go through the agreed contract administration route.

3. Subcontractor management protects specification compliance

Every specialist subcontractor on an MTB project is appointed against a written specification and programme. Shop drawings and method statements are submitted for architect review before fabrication or installation begins on packages where design intent is at risk — joinery, ironmongery, feature finishes, specialist lighting, and structural glazing in particular. We do not allow subcontractors to substitute materials without a formal architect instruction.

RIBA Stage 6: Handover — Practical Completion Done Properly

Practical completion (RIBA Stage 6) is one of the most contractually significant moments in any project. It triggers the release of retention, starts the defects liability period, and — if mishandled — creates disputes that damage both the contractor's and the architect's relationship with the client. MTB's approach to handover is methodical.

Four weeks before the target practical completion date, MTB conducts an internal pre-completion inspection and produces a snagging schedule. We resolve identified items before the architect's inspection wherever the programme allows. The architect is invited to attend a joint snagging inspection with MTB's site manager. Any items on the architect's snagging list are acknowledged in writing and assigned to a named individual with a completion date.

At handover, MTB provides the client and architect with a full Health and Safety file (as required under CDM 2015), operation and maintenance manuals for all building services, warranties and guarantee documentation, and a photographic record of concealed elements — drainage, structural connections, underfloor services — before they were covered up.

On residential projects that qualify, MTB offers a structural guarantee of up to 20 years. This gives the client — and, by extension, the architect's recommendation — a durable assurance on the quality of the work.

RIBA Stage 7: In Use — Defects, Aftercare, and the Long-Term Relationship

The defects liability period (typically 12 months under a JCT contract) is not the end of MTB's involvement — it is part of the service. When the architect issues a schedule of defects at the end of the defects liability period, MTB attends, completes the works, and signs off formally. We do not disappear after practical completion.

For architects who work on multiple projects, the defects liability period is also a signal of how a contractor will perform on the next project. MTB's defects record is something we are prepared to discuss transparently with any practice considering working with us.

What MTB Delivers at Each RIBA Stage — Summary

Why London Architects Work With MTB on Projects From £100,000 to £500,000+

MTB works on residential renovation and new-build projects across London Zones 1–4, with construction values ranging from approximately £100,000 to well above £500,000. Our portfolio includes rear and side extensions, loft conversions, basement projects, full house renovations, and whole-building refurbishments for both private clients and the residential investment market. You can see a selection at mytrustedbuilder.co.uk/portfolio.

Over 300 London homeowners have completed projects with MTB. Our YouTube channel, with more than five million views, demonstrates the transparency and documentation culture that runs through our site operations — the same discipline that makes us reliable partners for architects who need a contractor they can stand behind.

MTB is not the right contractor for every project. If a project is below our minimum value threshold, requires specialist conservation or listed building expertise outside our current capability, or needs a procurement route we cannot serve, we will say so at the outset. What we will never do is take on a project and then fail to deliver it to the standard the architect's design deserves.