Converting Half of a Double Detached Garage



You should at least read “Single Attached” to get an idea regarding roofs etc before reading this article.

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

So, just like before, let’s price for the most basic job you can do and build up from there.

The basic job (assuming a pitched roof)

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

A correctly insulated, and fire protected, timber and plasterboard stud wall built right down the middle.

A correctly insulated, plasterboarded stud wall, directly behind the up and over door. (We’re assuming there are 2 doors, 1 for each side).

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

An insulated, plasterboarded half 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 one electric heater, two 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, 10 days, plus a sparks for a day.

Labour………………….. £2700.00
Materials…………………£1600.00
Building control………. …£350

Basic Job Total …….£4650.00


The following prices are in addition to this basic job.
Maybe you also have to

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

Actually dig out the old floor (because it's too high possibly), and lay a new concrete "base slab" before undertaking the above, "basic job" floor work £1000.00

Convert half an existing flat roof to a warm roof (see “Job 4”)…………..£1000.00

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

Take an electricity supply to the garage…………£500.00

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

Bricking up the existing “up and over” door (on a new foundation), to comply with current regulations.

This price is minus the amount previously included in the basic job for masking the door. £750.00

Converting the 2 exterior 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 these walls £300.00

Building an insulated cavity wall down the centre rather than a timber stud wall.

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 building the stud wall…..£500.00

Plastering all the walls and ceiling £400.00