Garage conversion cost per m2: what the job involves and who is registered to do it

How garage conversion cost per m2 works

1. Separate the once-only work from the work that scales. Once: the floor build up decision, filling the door opening, the new circuit and consumer unit work, the heating connection, the building control application. Scales: insulation area, plasterboard, skim, decoration and flooring. On a single garage the first list is the larger share, which is why the rate looks high.
2. Measure the finished room, not the garage. Internal insulation on the walls and a raised insulated floor take real dimensions out. A rate applied to the garage's external footprint prices a room that will not exist. Take the finished internal size and use that for any comparison.
3. Ask what the rate is quoted against. A rate for a shell conversion, plastered and no more, is not comparable with a rate for a finished room with flooring, decoration, heating and a certificate. The same job carries two rates that can differ by half depending on where the line is drawn.
4. Use the rate to sense check, never to budget. Build the budget from the schedule of eight lines and then look at what the rate comes out as. A rate well outside the normal band is a prompt to ask which lines are missing, which is the only thing it is good for.

Insurance and paperwork

Common questions

Why is a single garage so expensive per square metre?

Because the fixed work does not shrink. The floor still has to be dealt with, the opening still has to be filled, the circuit still has to be run and the application still has to be made, and those costs are then divided by around fifteen square metres.

Does a double garage cost half as much per square metre?

Less than half as much again in some cases, because the fixed costs spread over twice the floor and the door opening work is often not doubled. That is the clearest illustration of why the rate is not a property of the job.

Is a per square metre figure ever useful?

As a sanity check between two quotes for the same scope, yes. As a way of estimating a job you have not scoped, no, and it is the commonest way people arrive at a budget that is out by a large margin.

Registered contractors by region

• Registered roofers in the East Midlands postcode area
• Registered roofers in the East of England postcode area
• Registered roofers in the London postcode area
• Registered roofers in the North East postcode area
• Registered roofers in the North West postcode area
• Registered roofers in the Scotland postcode area
• Registered roofers in the South East postcode area
• Registered roofers in the South West postcode area
• Registered roofers in the Wales postcode area
• Registered roofers in the West Midlands postcode area
• Registered roofers in the Yorkshire and The Humber postcode area