Should you project manage your extension or leave it to the experts?

man holding floor plans in building site
(Image credit: Getty Images)

If you are considering taking on the role of extension project manager for your own build then you would certainly not be alone — many people choose to take charge of their own extensions.

That said, when building an extension there are some important considerations to bear in mind if this is a path you are thinking of going down and it may well be that, for you, it will make far more sense to use the services of a professional with lots of experience with the type of project you are undertaking. 

Here, we explain exactly what the role of extension project manager entails, as well as the pros and cons of undertaking the job yourself so that you can be sure you are making the right choices when it comes to ensuring your extension runs smoothly from start to finish and results in the home of your dreams. 

What does a project manager do?

Before you can even begin to think about whether or not project managing your own extension is the right option for you, it is vital that you understand exactly what a project manager does and the full requirements of the role. 

So, what is a project manager? In short, a project manager on a build project of any kind, be that an extension, renovation or self build, is there to coordinate everything and to see that the extension is completed on time, within the client's budget and to the expected standards.

Coordinating a project means managing the various trades involved in an extension (builders, plumbers, electricians, roofers and so on) to work on each element of the  job at the right time. In addition, a project manager must liaise with and organise suppliers and designers — for example the kitchen supplier, glazing supplier and flooring fitter. They might also organise other essentials, such as skip hire and schedule deliveries of materials in such a way that they won't cause delays or clash with one another. And, finally, they should also have a great set of contacts in order to get you the best possible prices on the materials and products you want.  

Very often, the people who act as project managers will also have another role too. 

"A professional project manager (PM) may well have an additional role in the project, such as being the architect or quantity surveyor, for example, but this does not take away from the skills that they will bring once they put their PM hat on," explains Bob Branscombe, one of the UK’s leading chartered surveyors.

Is project managing your extension a good idea?

There are many benefits of project managing your extension as opposed to handing the reins to someone else. 

"Ultimately, there are two big reasons to manage your own extension project — control and cash," says former Editor of Homebuilding & Renovating magazine Jason Orme, who is also an experienced self builder and has recently finished renovating his 1960s home. "The control is arguably more important, because taking on the builder's role enables you to ensure every decision is yours to make. That's a big win when it comes to the larger decisions – such as choosing the key trades, like bricklayers – but also pretty arduous when it comes to the 'I'm not too sure I really care' decisions which have less of a cost, performance or visual impact. That said running the labour and materials means it's all within your gift and as a result, you get what you want.

"And, of course, the money's nice, too. Removing the main contractor's salary from the project can be a significant five-figure saving, which all counts," continues Jason. "And, because you're controlling the chequebook, you'll be more likely to drive down costs in other areas too, rather than just allowing your main contractor to deliver stuff to your door and add their 20% (or so)."

What skills will you need to project manage an extension?

There are certain skills that will really come in handy when it comes to project managing your extension and it will help if these come naturally to you. So, could you handle project managing your building project? Ask yourself the following questions before you commit: 

  • Do you have any experience? It really does help if you have carried out an extension project before if you are thinking of project managing. Even if you have only modernised or renovated, some knowledge of how building projects work is going to be really useful. 
  • Are you organised? Natural organisers are going to find the job of project managing far easier than those who lean towards 'winging it'. "Running a good to-do list is key to every successful project," says author of the Housebuilder’s Bible and experienced builder Mark Brinkley. "Some miraculous people do this entirely in their heads, but most of us need to write it down in order not to overlook items. The to-do list needs to be updated frequently, and also to be acted on.
  • Are you good with numbers? If you don't want to ending up going way over budget, a head for numbers will come in really handy. 
  • Are you good at negotiating? Confident negotiation skills are hugely important when it comes to project managing — from getting the best deals on materials to juggling niggles between trades. And don't forget the neighbours either. "It is well worth taking time out to chat to neighbours and explain what you are doing and when you plan to do it," suggests Mark. "They tend to be far more amenable if you can give them confidence that you are managing the process properly so that it will be as quick and painless as possible."
  • Do you understand how to order building materials? It may well be the case that ordering materials will fall to you, as project manager. "Many subcontractors work on a labour-only basis and expect you to have purchased all the materials they need and for them to be ready on site at the scheduled hour," explains Mark. "If you haven’t a clue, then this would be a useful moment to hire the services of a quantity surveyor."
  • Are you a ditherer? If so then now could be a good time to ditch the idea of project management. You need to be clear about what you want at every stage of your extension in order to get the desired end result. Decisions come hard and fast and too much dithering will waste time and money. You also need to avoid changing your mind at the last minute. 

measuring house plans

Project management involves juggling many different elements of a build — usually all at once.  (Image credit: Getty Images)

What are the advantages of acting as project manager?

If you do decide to take on the responsibility of project managing your own extension, what benefits can you expect to enjoy?

  • Considerable savings: You can expect to save between 10-20% of the overall costs of the project by taking on this role yourself.
  • Personal team selection: You get to choose the people who will be working on your extension rather than just being presented with a team who you might not have a good rapport with.
  • There will be no unwanted surprises: As you will be overseeing each step of the build, there is less chance that you will return home to find a decision has been made on your behalf that you would not have made yourself.
  • Greater control: As project manager, you will have more control over the final outcome — that could be something as little as realising before it is too late that the wall tiles which are about to go up are slightly the wrong shade or that the light positioning needs tweaking a bit.

What are the disadvantages of project managing?

Of course just as there are upsides to project managing your own extension, there are also some downsides to bear in mind. 

  • It is hard work: Don't underestimate the practical side of project management alongside the 'overseeing' side. "Tasks such as keeping the site tidy, stacking and storing materials, site security, taking in deliveries and temporary weatherproofing all fall on the project manager," says Mark Brinkley.
  • There are greater risks to consider: "Savings may be made, if you are organising and employing the various contractors directly and ordering materials, but with it comes greater involvement and risk," says architect David Nossiter of David Nossiter Architects. "Contractors charge what are termed preliminary costs. These are the overheads of the site set up and daily organisation, as well as profit and it is these areas where savings may be made. You would be dealing with items on a daily basis, ordering materials in good time, arranging for deliveries, licences, organising trades, dealing with building control and working against an overall programme. You would also be responsible for health and safety on site. If in the event of being let down by a sub-contractor or by materials not arriving on time you are responsible for any delays."
  • Timescales are usually longer: The job of a project manager is a full-time one and unless you are dedicating all your time to the role then you may well need to accept that your extension will take a good few weeks or months extra to complete. 
  • You will always be in the firing line: As the first point of contact, if things go wrong, it will be you that trades, planning officers and angry neighbours will come to with their complaints or issues. Be prepared to do plenty of negotiating.
  • You may lack contacts: The professionals who usually take on the role of project manager, be that an architect or main contractor, will usually have a hefty list of trusted contacts in terms of tradespeople and suppliers.

What are the alternatives to project managing yourself?

Of course there are many project management routes to consider alongside taking a DIY approach. 

Main contractor: Hiring one main contractor for your extension is actually a brilliant idea. In general, a main contractor will be your builder, who you hopefully will have chosen because they came with trusted recommendations and you felt you had a good rapport with them. Your main contractor will either employ all various trades directly, or will have a selection of third party trades who they regularly use. They can make sure that the right trades or suppliers are there at the right time and can check that work is completed to a high standard. 

"If you have a main contractor there will be several aspects to your role," explains architect David Nossiter. "Maintaining cost control will be critical. You will also have to check workmanship and that the build is as per the drawings and agree any site issues. Alongside this you will need to verify the progress of the individual trades to ensure that they align with the overall programme, whilst keeping an eye out for any potential delays to the works. You will also have to decide in an impartial manner whether events on site have cost and time implications. Under a traditional contract with a main contractor who employs sub-contractors, all of this falls within the remit of the contract administrator, usually the architect."

Package company: If you are building an oak framed extension, the supplier can often oversee the whole thing, from design stages right up to completion. They will have builders and suppliers who they regularly work with. 

Architect/designer: If you have hired an architect to design your extension then many will also be able to take on the role of project manager. They usually have excellent contacts and will be able to answer all queries that come their way. 

How much does a project manager cost?

One of the main reasons people decide to project manage their own extension is to save money — but how much could you realistically expect to save?

"The fees payable are generally estimated in the first place by a percentage proportion of the estimated cost of the project — this gives the PM an idea of the fee level they are quoting you," explains Bob Branscombe. "Make sure you convert this estimate into a fixed lump-sum agreement for the services, otherwise you are at the mercy of rising construction costs and variations which will compound in the fees you are paying!"

Natasha Brinsmead

Natasha is Homebuilding & Renovating’s Associate Content Editor and has been a member of the team for over two decades. An experienced journalist and renovation expert, she has written for a number of homes titles. Over the years Natasha has renovated and carried out a side extension to a Victorian terrace. She is currently living in the rural Edwardian cottage she renovated and extended on a largely DIY basis, living on site for the duration of the project. She is now looking for her next project — something which is proving far harder than she thought it would be.