Turnkey or beam only?
Having only the beam installed and coordinating the rest yourself costs less on paper. Turnkey becomes the better deal as soon as the project involves more than two trades, because the real cost then shifts from materials to waiting time between contractors. The tipping point is usually the underpinning.
What each approach covers
Beam only. A contractor removes the wall, installs the beam and columns according to the sealed plans, and leaves. You keep responsibility for the underpinning if it's required, for moving the plumbing and electricity that ran through the wall, for closing up, the floors and the paint.
Turnkey. A single contract covers everything from the survey to the finishing, including coordinating the engineer and the permit.
Who's responsible if something goes wrong
That's the real difference, and it doesn't show in the quote.
In a fragmented approach, every contractor is right within their own perimeter. The structural contractor will say they installed the beam according to the plans. The plumber will say they connected what they were asked to. The finisher will say they finished what was handed to them. If the floor moves two years later, there's nobody to put the question to, and the owner becomes the referee of a technical debate they don't have the means to settle.
With turnkey, there's one name on the contract.
The real cost of a site that waits
A fragmented site doesn't cost more in labour. It costs more in dead time.
The electrician can't come before the structure is done. The plasterer can't come before the electrician. Everyone has their own schedule and their own emergencies elsewhere. When one link slips by a week, it isn't a week of delay: it's a week plus the next available slot of the following trade, which is often two or three weeks further out.
If you live in the house during the work, that delay has a real cost. If you rent it out, it has another.
How to know which case you're in
Beam only is a reasonable choice if you have experience managing a site, if you already have trusted people in every trade, if the project doesn't require significant underpinning, and if you're available during the day.
Turnkey is the right choice if the project touches the structure and the mechanics at the same time, if nobody can be on site during the week, or if you want one person responsible in case of a problem.
There's no universal right answer. There's an answer per project, and we'll give it to you honestly on the phone, even when it doesn't favour us.
So, what are we working on?
Eight questions, two minutes. We call you back to talk it through, and we tell you frankly whether it's a project for us or whether you'd be better served elsewhere.