Construction management or a main contractor: who carries the risk

Now the other route, and this is where most people have already been misled, usually by Google.

Under construction management in the UK, you do not hand the whole job to one firm. You contract directly with each trade yourself. The bricklayer, the electrician, the joiner: each holds a separate contract with you, and each parcel of work is a trade package. A construction manager is the professional you pay to run all of it. They plan the sequence, coordinate the trades and keep the programme moving. But they are your agent, which means they act on your behalf. They do not hold the contracts with the trades, and they do not hold the contract with your design team. You do. The arrangement is established enough to have its own standard industry contracts.

The construction manager is paid a fee for the service, rather than building the job for a profit margin, and the cost of the actual work is usually shown to you in the open, line by line. That openness has a name in the trade: open book.

Here is the trap. If you searched for construction management against a main or general contractor, most of page one was written for the American market, and the American term means close to the opposite of the British one. In the United States a construction manager often holds the trade contracts and carries the risk of the work, which is much nearer to what Britain calls a main contractor. Even Procore, one of the largest US construction software firms, accepts that the British equivalent of the American general contractor is the main contractor. So the articles that confused you were not wrong about America. They were just not about Britain.

Two things construction management is not. It is not project management with a grander title; it is a way of procuring and running the whole build, not keeping a diary of it. And it is not a trick for cutting the contractor out so you pocket the difference. It needs a real team and real management to work at all.

Both routes arrive looking like the same task: agree a price, then build. That is the disguise. The real difference sits underneath, and it is this. Who carries the risk of the part of your project that has not been drawn yet.

Because on every renovation, a great deal of it has not. The drawings you signed off are never the whole story. There are decisions still to make, conditions still to uncover, details left to settle on site. Somebody has to price that uncertainty, and the two routes price it in opposite ways.

A main contractor prices the job against drawings that are not finished. So the firm does the only sensible thing with the gaps: it guesses. It prices the unknown high to stay safe, or excludes it from the quote, or leaves it to be argued over later as a variation. This is why a fixed price is one of the more misleading phrases in the business. The standard building contracts are not, in law, promises to deliver everything for one untouchable figure. The price moves: through changes you ask for, through cost rises the contract allows, and through claims for extra time and money. A fixed price names the start, not the finish. What a single quoted number leaves out is a subject of its own.

Construction management meets the same uncertainty from the other end. The trade packages are let in stages as the design develops, sometimes before the whole design is even finished. So the undrawn parts are not buried in one early number. They surface as the job moves, and they are priced in the open, line by line, as the real cost of the actual work. The trade-off is honest and it is real: there is no single agreed price at the start, you do not know your full cost until the last package is let, and changing a package that has already been let can be expensive.

So the question was never which route is cheaper. It is who carries the risk of what no one has drawn yet.

Once the work starts, the choice comes down to three things: what you pay, how much you carry, and what happens if a firm fails.

On cost, the main contractor route gives you certainty that looks complete and is not. You get a number at the start, which is reassuring, but it includes a premium for the risk the contractor has taken on, and the final account still moves as the job throws up changes and claims. Construction management gives you the opposite shape. You see the real price of each trade in the open, with no contractor's margin on top, but you reach that clarity by carrying the risk and the coordination yourself. The construction manager is paid a fee for managing the work, plus the genuine costs of running the site. There is no standard figure for that fee worth quoting: the route is used on too few prime homes for an honest market number to exist. Working out what a specific project should cost is a separate exercise again.

On burden, this is the part that gets sold short. Construction management suits an experienced, hands-on client with a professional team around them and the time to give. You are signing many contracts and working with many consultants, not handing it all to one firm and stepping back. The trade is plain. The route only works for clients who can carry it.

Then the failure case, and here the difference is sharp. Construction sees more firms go under than any other sector in the UK, with 3,827 firms going under in the year to March 2026. If your one main contractor is among them, the whole job can stop at once. Its unpaid subcontractors walk off, and you can find yourself paying twice for work you thought was covered. Under construction management you hold every trade contract directly, so one trade failing means re-letting one package, not the collapse of the entire project. Legal analysis of these arrangements makes the matching point: the risk of a trade going under rests with you, because the trade contracts are yours. That cuts both ways. The route protects the whole from one failure, but you carry the cost and the coordination of the re-letting, and your construction manager, as your agent, manages it rather than absorbing it. Picking up a build after a firm has walked is its own problem to manage.

Strip it back and the decision is a bet. You are betting on how much of your project is still unknown, and deciding who absorbs the cost of finding out.

On a new build on a clear site, the unknown is small, and a single price is worth a great deal. On a prime period property it runs the other way. Victorian and Georgian buildings hide their problems behind the walls: damp, movement, rot, and old services that only show themselves once the plaster is off. The drawings cannot show what no one has seen. Timelines stretch when those discoveries surface, and in Kensington, Chelsea or Mayfair you add tight access and the rules of the estate you are building within. The undrawn scope on this kind of job is not a rounding error. It is the job.

This is why construction management, marginal by sheer count, has long been used far more on high-value work. A 2001 RICS survey found it made up a tiny share of contracts by number but a far larger share by value. The expensive, complicated jobs are where the open-book approach earns its keep, because the route that prices the unknown in the open, rather than hiding it in one early figure or fighting over it later, gives real cost control when the unknown is large. With one condition. It only works if the management is good and the undrawn scope is defined properly before any price is fixed.

That last point is where Myrmex sits, inside the same reality as every firm above and not above it. Construction management moves coordination and risk onto the client. That is simply true of the route. The work is to carry that management well, and to push the hard thinking about the unknown into the pre-construction stage, so the undrawn scope is reduced before a price is fixed rather than argued over once the walls are open. That does not remove the unknown on an old building. Nothing does. It just means you meet it on purpose, early, instead of by surprise, late.