How to project manage an extension or renovation

Knowing how to project manage an extension or renovation is a great way to save money when you're on a strict budget, but will require more responsibility. Find out exactly what's involved

How to project manage an extension or renovation: Exterior of renovated school house and garden
(Image credit: Bruce Hemming)

Knowing how to project manage an extension or renovation can help you minimise costs and stay on budget. Managing your own project when extending a house or renovating a property does require a lot more planning and responsibility, so it's important to make sure you're aware of what will be required before taking on the role. 

Providing a realistic insight into the day to day requirements of the role, as well as tips on hiring sub-contractors, handling money and VAT, our guide is here to help you decide whether taking on the role of project manager is for you.

If you are extending a house, find out more about the process in our ultimate guide. Our step-by-step guide to renovating a house will be vital, too, if you're taking on such a project. 

What is the project manager's role?

Budgeting is an important part of the project manager's role. Our extension cost calculator can give you an idea of how much you should expect to spend when extending your home – this will be handy when working out budgets.

The project manager's role is to take your drawings and chosen fixtures and finishes, and to deliver a completed home, just the way you want it, within a set budget and timescale. This can take away the pain of organising a home-improvement project, meaning all you have to focus on is selecting the look and paying the bills.

Use our week by week extension planner to ensure you keep your extension or renovation project to schedule.

In addition to taking responsibility for the build, they should oversee the contractor and/or subcontractors, as well as dealing with your local authority’s planners, building control, health and safety, and utility companies.  For large projects under a formal contract, they may also take on the role of contract administrator, or be responsible for appointing an independent professional in this capacity. 

They will also co-ordinate the rest of the design team and any other professional consultants involved in the projects, these may include:

  • Structural engineer
  • Tree consultant
  • Ecologist
  • Historic building specialists
  • Archaeologists

extension clad with brick slips to give contemporary feel in keeping with rest of home photographed by Will Pryce/Arcaid Images

(Image credit: Will Pryce/Arcaid Images)

Does every project need a project manager?

Generally, extensions, loft conversions and internal alterations require a main contractor to co-ordinate the management of the build. However, an independent project manager is not usually involved – you could decide to take on the responsibilities yourself, with the architectural designer in the background providing advice and design detail as requested.

For larger or more complex improvements, the role of project manager and contract administrator is often handled by the lead architect, perhaps in conjunction with a quantity surveyor to provide interim valuations for completed work. 

This might suit you if you have limited time or knowledge and want to leave the job to the professionals. Project management services are also offered by professionals from other disciplines, including chartered building surveyors and quantity surveyors (, members of the Chartered Institute of Building, Architectural Technologists and even some interior designers.

Some project managers also provide construction services, overseeing the organisation of the work in place of a main contractor. In this instance they are also responsible for establishing the build schedule, and managing the budget and cash flow. They will be involved in finding and managing subcontractors and supplying materials, plant and tools.

Can the role be divided?

When project managing an extension or renovation, and depending on the scale and complexity of the building work, the different facets of project management can be undertaken by a single agent, such as the lead architect, or divided between others such as a quantity surveyor to control the budget and a main contractor running the build.

How much will it cost to hire a project manager?

Naturally, for the convenience of leaving all the organisation to someone else, you have to pay a price. Fees for contract administration (engaging and managing the main contractor) vary from 3 to 15 per cent of the contract value (the total cost of construction works).

Fees on small projects tend to be disproportionately high because of the fixed costs, while percentages for larger projects will be towards the lower level. If your project manager is also taking on the role of contractor and organising construction work, fees will be higher.

They may charge a fixed day-rate for their time, or work on a prime-cost basis, plus a fixed margin, ranging from 20 to 25 per cent for smaller works, down to 10 to 15 per cent for large projects.

An external shot of the front of the Victorian house, with black painted front door

(Image credit: Katie Lee)

Can I take on the role of project manager myself?

Acting as your own project manager on an extension or renovation can save on professional fees for contract administration and many home improvers decide to take on this challenge, working in conjunction with a main contractor.

Some also take on the role of contractor, hiring subcontractors and tradespeople directly. Managing a large home-improvement project such as this is a huge commitment but, provided that you undertake the role effectively, can mean making savings of as much as 10 to 15 per cent.

In practice, though, while the rewards can be considerable, owner-run projects tend to take longer to complete. And, you must do your homework first to ensure that every part of the job, completed by each trade, is exactly as it needs to be. If you don't brief your trades properly – due to a lack of knowledge – the next part of the job will inevitably be held up while work is done to correct or improve on the previous stage. These delays will, inevitably, lead to extra cost.

If, ultimately, you decide that project managing is for you, ensure you have put aside a decent contingency fund (at least 10 to 15 per cent of the project cost) to cover any extra costs incurred.

The back of the cottage has a courtyard area leading back into the house through grey bi-folding doors

(Image credit: Jeremy Phillips)

What are the basics a project manager needs?

  • Calendar
  • Printed plans pinned to a wall on site
  • Scale ruler for measuring materials to be ordered
  • Tape measure for checking key dimensions
  • Digital camera to record progress for payment
  • Broom and cleaning materials
  • Work gloves, boots and hard hat
  • A portable toilet for the builders to use

What is required day-to-day?

Project managing an extension or renovation includes organisational jobs; this means scheduling the work and making sure your subcontractors know well in advance when they are required and turn up on time, knowing exactly what they will be doing and have everything they need to carry it out.

Much of the project management work can be done in the evenings and at weekends, but inevitably some tasks – site meetings, ordering and sourcing building materials and son on – have to be done either in or around working hours. You have to be sure that you have the time and the skills to do the job effectively, especially if you are in full-time employment.

How do I find good subcontractors?

If you're determined to project manage an extension or renovation yourself, the best way to find a good builder is through recommendation (use our guide to find out how). Although this does not guarantee that the subcontractor is not a cowboy builder (again, use this guide to find out how to avoid them), it does mean it’s far less likely that someone working on a personal reference will jeopardise their livelihood by letting you down and damaging their reputation.

Tradespeople are always aware that they are only as good as their last job. Once you have found one good reliable subcontractor, you are on your way, as they will have worked with many others whose work they know and respect.

This can prove a useful source of contacts as a good tradesperson is unlikely to recommend someone unreliable or incompetent – especially if they are going to be working with them or after them.

Networking within the trade is very important and works both ways: if you’re a good employer and are fair and pay on time, word will get around, just as it will if you are a ‘cowboy client’.

Checking subbies' credentials

Many subcontractors and tradespeople are members of a trade body or guild that acts as an industry regulator and standards authority, and also helps to promote members. Some trades, such as electricians and plumbers, have to be members of a trade body or certification scheme, as they are the statutory regulators of industry safety standards.

The Trustmark scheme is a government initiative designed to help the public find reliable and trustworthy building contractors and tradespeople. It has a vetting procedure and awards the Trustmark to those who comply with government-endorsed standards.

When hiring, consider the following:

  • Make sure they have relevant experience
  • Check their availability
  • Get references and check them out in person
  • Discuss how they will price for the work
  • Let them know any unusual materials or techniques

glazed extension attached to victorian terraced house by IQ Glass

(Image credit: IQ Glass)

When should I pay the builders?

For a smaller job taking a week or two, you should agree to pay for the work in full once you are satisfied it has been completed properly. For larger jobs, you should agree on regular stage payments; for example, first-fix then second-fix for plumbers and electricians, or weekly or fortnightly payments for bricklayers and carpenters.

Make sure you structure the payments so that they are always working a week or two in advance of their payment. Never pay for anything upfront. If a subcontractor asks for funds in advance to buy an expensive item – such as a plumber needing to get the boiler on site – it’s best to pay for the item yourself, in your name. You should still benefit from their trade discount.

Do I have to pay VAT?

Most renovation work attracts VAT at the standard rate of 20 per cent; however, if a subcontractor is not VAT-registered, they must not charge it on their labour.

Using individual tradespeople whose turnover means they do not have to register for VAT can mean a significant saving on labour costs. If your project is eligible for any concessions, such as the reduced rate for dwellings empty for two years or more, you will only benefit if you use VAT-registered subcontractors.

Make sure that the subcontractor is aware that the work is eligible for a concession and that the appropriate rate is charged.

Project management checklist

If you do decide to take on the role of project managing an extension or renovation, this preliminaries checklist will keep you on track when it comes to organising your project. There are a number of arrangements to be made, including:

  • Discharge any planning conditions
  • Arrange any Party Wall settlements with the tenants and owners of adjoining properties
  • Notify building control
  • Arrange utility disconnections/connections
  • Plan the layout of storage on site
  • Get insurance in place
  • Make the property secure with fencing if required
  • Arrange welfare facilities, a rest area and WC
  • Plan for compliance with health and safety
  • Check access for deliveries
  • Notify all subcontractors
  • Check lead-in times for materials orders
  • Check your title deeds and lease
  • Check all boundaries
  • Arrange skips and scaffolding, plus any permits required for street closure
  • Check for tree preservation orders
  • Arrange a building warranty or guarantee

Find more information for planning and carrying out your extension: