Converting a single attached garage

Right then, the differences between an attached garage and an integral one, are …

The roof………. It has one for a start, which is external to the house and it will need insulating.

A rear wall…… this wall is exposed to the elements and will also need insulating.

There may also be an external rear door, which relevant to the basic price, we are assuming you will leave as it is, or just build across it.

The roof’s not a problem if it’s pitched. A ceiling can be created, insulation laid on top and a couple of ventilators fitted.

Insulating and ventilating flat roofs is more complicated. It’s very likely that an existing flat roof has no insulation and probably no ventilation.

If this is the case a “warm roof” can be created by fitting insulation outside, on top of the existing flat roof, (I know it sounds daft), then laying a new flat roof on top of that.

The old existing felt acts as a vapour barrier and no ventilation is required.

Make sure your builder knows exactly what he’s doing relevant to insulating (and ventilating) the roof, or you will get condensation problems!

The building inspector will be invaluable here.

So, with the roof organised, just as before, let’s price for the most basic job you can do and build up from there. Have a look at our article… “Single Integral Garage”


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 existing exterior brick (side and rear) walls.

A timber, insulated, plaster boarded stud wall, directly behind the up and over doors.

An insulated, plaster boarded ceiling, with ventilation above.

No plastering, just tape and fill the joints between the plasterboards and paint the room, (including the untouched internal house wall).

Fit one radiator, two electrical sockets, one central light and switch, skirting boards, architraving around the rear external door if you leave it in and probably a bit of boxing to hide the gas meter.

That will take two blokes on £150 and £100 per day respectively, 9 days, plus the same sparks and plumber, for a day each …….

Labour………………….. £2650.00
Materials…………………£1400.00
Building control………. …£350

Basic Job Total …….£4400.00


The following prices are in addition to this basic job.

Maybe you also have to……..

Create a new flush internal door from the house…………£550.00

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…………..£1000.00

Convert an existing flat roof to a warm roof……..£900.00
This price takes into account the ceiling and insulation included in the “basic job” price.


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

Bricking up an existing rear door……..£325.00

Putting in a side or rear window ………£700.00.

Removing the garage doors, laying a new foundation and building a wall and 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. …………..£1300.00

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…..£300.00

Plastering all the walls and ceiling……….£400.00

Putting in underfloor heating connected to your boiler…………..£550.00
This price is minus the amount we included in the basic job for fitting a radiator.