Do You Need a Project Manager for Your Building Project? What They Do and What They Cost

**Model 1 — Main contractor with principal contractor responsibility**:

• The client appoints a single main contractor (such as RCB Design & Build). The main contractor:
• •Takes responsibility for coordinating all trades (their own directly employed workers plus subcontractors)
• •Manages the programme, ensuring trades arrive in the right sequence
• •Manages procurement (materials, plant, specialist contractors)
• •Manages the site (welfare, safety, security, access)
• •Takes CDM (Construction Design and Management) duties as principal contractor
• •Issues variations with agreed costs before the work is done
• •Provides a single invoice to the client for the agreed contract sum (plus approved variations)

*Client's role*: Approve the scope and design; make payments at agreed stages; make decisions when requested (design choices, variations); be available for the contractor's questions.

*Advantages*: Single point of accountability; the client's time commitment is low; the contractor carries the risk of programme overrun and trade coordination failure; appropriate for the majority of domestic renovation and extension projects.

*Disadvantages*: The main contractor's margin (typically 15–25% of the subcontract and materials cost) is included in the contract sum; the client does not see the underlying trade costs.

**Model 2 — Client self-management (multiple direct trades)**:

The client appoints each trade directly (groundworker, bricklayer, roofer, carpenter, electrician, plumber, plasterer, decorator, tiler, kitchen fitter). The client coordinates the sequence, resolves clashes, and manages each trade's performance directly.

*Client's role*: Full programme management; coordination of all trades; procurement of all materials; resolving conflicts between trades; managing quality; dealing with non-performance.

*Advantages*: The main contractor's margin is saved — the client accesses trade costs directly. In theory, this saves 15–25% of the contract sum.

*Disadvantages*: The time commitment is enormous — self-management of a significant building project is effectively a part-time job, typically requiring 2–4 hours per day of active engagement during the construction phase. Programme overruns are common (trades are not coordinated by a professional who understands the critical path). Trade selection without professional screening produces variable quality. Procurement gaps (a trade arrives and the materials haven't been delivered) cause delays. CDM responsibilities for a project with multiple contractors must be discharged by the client, who may not understand them. The savings are typically illusory — the programme extension, disputes, and rework caused by poor coordination cost more than the contractor's margin.

*When self-management works*: For very small projects (a single trade, a defined piece of work), or for experienced self-builders who have done it before and have the time.

**Model 3 — Client-side project manager**:

• An independent project manager (PM) is appointed by the client to coordinate the project on their behalf. The PM may either:
• •Manage a package of direct trade contracts (acting as the coordination layer between the client and the individual trades)
• •Act as employer's agent on a main contractor appointment (reviewing the main contractor's programme, quality, and claims on the client's behalf)

*Client's role*: Brief the PM; make strategic decisions; attend key meetings and sign-off milestones; pay the PM's fee plus the trade or main contractor costs.

*PM's role*: Programme management; trade or contractor management; procurement coordination; quality checking; cost reporting; variation management; contractual administration; client reporting.

• *When a client-side PM is appropriate*:
• •Large, complex projects (£150,000+) where the main contractor appointment itself needs professional oversight
• •Projects where the client wants independent quality checking of a design-and-build contractor's work
• •Projects where the client has significant other commitments and genuinely cannot engage with the programme decisions that arise daily
• •Projects involving multiple contracts or multiple sites

**What a PM does — in a residential context**:

• *Pre-construction phase*:
• •Reviews the design and specification for completeness (identifying gaps that will cause problems on site)
• •Prepares a pre-construction checklist (party wall awards served; Building Control notified; structural engineer's design received; materials with long lead times ordered)
• •Coordinates the programme with the contractor — checking that the proposed sequence is logical and that the critical path is correctly identified
• •Reviews the contract documents for adequacy

• *Construction phase (active management)*:
• •Weekly site visit to review progress against programme, quality of workmanship, and compliance with specification
• •Attends key programme milestones (foundation inspection before pour; structural steel arrival and installation; roof completion; first-fix signoff)
• •Issues variation orders where scope changes and agrees costs before the work is done
• •Reviews and certifies the contractor's payment applications — checks that the completed works justify the payment requested
• •Keeps a site diary (a contemporaneous record of events, decisions, and progress — invaluable if a dispute arises)
• •Reports to the client weekly: current status, costs, next week's planned activities, any issues requiring decisions

• *Post-construction phase*:
• •Produces the snagging list at practical completion — the itemised list of defects and outstanding items
• •Tracks the contractor's resolution of the snagging list
• •Recommends the release of retention at the end of the defects liability period once all snagging items are resolved
• •Assembles the project documentation for handover: warranties, Building Regulations certificates, as-built drawings, O&M manuals for any installed equipment

**What a PM costs**:

• Project management fees for domestic residential projects in London are typically charged as either:
• •A percentage of the project value: typically 5–10% for a hands-on PM on a residential project (at the higher end for complex projects and for PMs who are also managing multiple contracts; at the lower end for lighter-touch oversight on a main contractor appointment)
• •A fixed monthly retainer: typically £800–£2,500/month for a part-time PM involvement (1–2 site visits per week plus administration)
• •An hourly or day rate: typically £350–£700/day for an experienced construction PM in London

For a £100,000 extension project with a main contractor: a project manager providing weekly site visits, payment certification, and variation management for 16 weeks of construction would typically cost £3,000–£7,000 — approximately 3–7% of the project value.

**When is the PM cost justified?**

• The PM cost is justified when:
• •The value of the decisions being protected exceeds the PM's fee — a PM catching a £5,000 specification error, a £3,000 variation that was never agreed, or a £10,000 payment overpayment pays for themselves many times over
• •The client's time is valuable enough that the alternative (self-managing) has a real cost to the client
• •The project is complex enough that trade coordination would be genuinely challenging without a professional intermediary

For a straightforward extension with a reputable main contractor, the main contractor's own coordination is usually sufficient — a separate PM adds cost without proportionate value. For a complex whole-house renovation, a multi-phase project, or a project where the client is frequently travelling or cannot engage daily, a PM adds significant protection.

**CDM 2015 — Construction Design and Management Regulations**:

The CDM 2015 Regulations impose duties on all parties involved in construction projects. For domestic clients (homeowners), the key CDM duties are:

• *On all domestic projects*:
• •The client must ensure a suitable Construction Phase Plan is produced before construction begins (the main contractor typically produces this)
• •The client must ensure a suitable Principal Designer is appointed where there are multiple designers/contractors (this duty can be passed to the principal contractor in writing)
• •The client must ensure welfare facilities are provided for all workers on site (the main contractor manages this in practice)

*Notifiable projects (projects lasting more than 30 working days with more than 20 workers simultaneously, or exceeding 500 person-days)*: The client must notify the HSE. Most domestic residential projects are not notifiable.

*For domestic clients*: CDM 2015 Part 4, Regulation 5(4) states that if a domestic client fails to make the appointments required (principal designer, principal contractor), the designer in control of the pre-construction phase is deemed to be the principal designer, and the contractor in control of the construction phase is deemed to be the principal contractor. In practice, for a domestic extension with a single main contractor, the main contractor takes on the principal contractor role as standard.

**What the principal contractor duty means**:

• The principal contractor under CDM 2015 must:
• •Plan, manage, monitor, and coordinate health and safety during the construction phase
• •Prepare and maintain a Construction Phase Plan
• •Organise cooperation between contractors on site
• •Ensure suitable site induction for all workers
• •Prevent unauthorised access to the site
• •Display the project's contact details and Construction Phase Plan on site

A reputable main contractor carries these duties as a matter of course. If you appoint multiple direct trade contractors without a main contractor, you (the client) must discharge these duties — which requires knowledge of CDM, site safety management, and the time to do so properly.

**Why this matters in practice**:

CDM compliance is not only a legal requirement — it also affects your insurance position. If a worker is injured on your domestic project and there is no Construction Phase Plan and no principal contractor managing site safety, your household insurance may not provide adequate cover, and you may carry personal liability for the injury.

For any significant building project with multiple contractors working simultaneously, ensure that the main contractor (or an appointed principal contractor) has clearly taken on the CDM principal contractor duties in writing, and that a Construction Phase Plan is produced and available on site from the start of construction.