Converting a double detached garage



Have a look at “Single Attached” and it’s info. about converting roofs, before you continue with this article.

Also we are only going to deal with brick built garages with “proper roofs”, not corrugated asbestos or prefabricated ones.

The basic job (assuming a pitched roof)

A damp proof membrane, insulation and screed, to create a new floor on top of the existing concrete one.

A vapour barrier, insulation and dry lining to convert the 3 exterior side and rear brick walls.

A timber, insulated, plasterboarded stud wall, directly behind both sets of up and over doors.

An insulated, plasterboarded ceiling, with ventilation above.

No plastering, just tape and fill the joints between the plasterboards and paint the room.

Assuming an adequate legal electric supply exists, fit two electric heaters, four electrical sockets, one central light and switch, skirting boards and architraving around the door and window.

That will take two blokes on £150 and £100 per day respectively, 14 days, plus a sparks for a day.

Labour: £3700.00

Materials: £2200.00

Building control: £350

Basic Job Total: £6250.00


The following prices are in addition to this basic job.

Maybe you also have to:

Actually dig out the old floor (because it’s too high possibly), and lay a new concrete “base slab” before undertaking the described, “basic job” floor work: £1400.00

Convert an existing flat roof to a warm roof £1800.00

This price takes into account the ceiling and insulation included in the “basic job” price.

Cut out for and fit a new PVCu door: £1000.00

Or replace the existing one: £750.00

Cut out for and fit a new PVCu side window" £700.00

Or replace the existing one: £400.00


Or, if you want to spend a bit more how about:

Removing the garage doors and central brick pier, putting in a new long lintol, laying a new foundation and building a wall and wide window across the front, to “match” the rest of the house.

This price is minus the amount previously included in the basic job for masking the doors: £2100.00

Converting the existing exterior side and rear walls to cavity walls.

This price includes laying a foundation (which would be done during the floor slab conversion).

We have also deducted from this price, the amount previously included in the basic job for dry lining the walls: £600.00

Plastering all the walls and ceiling: £500.00