How Much Of A Room Do You 'lose' To Plasterboard?

[mandimoo]

Wanting to do a garage conversion. Is brick built outside, breeze block inside. The width is currently 2.5m. How much width am I likely to lose to plasterboard?

[gingejbee]

The Builder should be along soon with an expert answer......

[jackthehat]

If the cavity is insulated, about 12.5mm (half inch) to each external wall face.

If not, somewhere in the region of about 75mm (3 inches) to each external all face.

[The Builder]

As Jack has said, Mandi. You could even reduce this if using 9.5mm plasterboard. It would be glued to the wall face.

Her other point is relevant. You will need to introduce some insulation to the walls. The blockwork may already be made of insulating blocks. If that isn't enough, then the added thickness will indeed amount to a loss of around 75mm (50mm "Celotex" insulation board plus 12.5mm plasterboard. )