Garage Conversion in Jersey: Planning and Bye-Law Guide

Converting a garage is one of the cheapest ways to gain a room, because the walls, roof and floor slab already exist. Two things make it less simple than it looks: what happens to the parking, and how much of the existing structure is actually fit to become habitable space.

Does it need planning permission?

Generally yes, for an integral or attached garage, because converting it changes the external appearance — the garage door is replaced by a wall and a window.

Work through the States’ garage conversions tool for your specific property. The answer turns on whether the property is listed, whether the work is within the domestic curtilage, and whether earlier permissions removed permitted development rights.

Two situations reliably need permission:

• Anything on a listed property or in a conservation area
• Converting a garage into a separate unit of accommodation — that is a change of use and a different, harder application. See change of use and garage to annexe.

The parking question

This is the one that surprises people, and it is worth raising before design starts.

Planning policy is concerned with parking provision. If your property was permitted on the basis of a certain number of parking spaces, removing a garage removes one — and the department will want to know where the car goes. On a house with a generous driveway this is a non-issue. On a tight urban plot in St Helier where the garage is the parking, it can be the thing that decides the application.

Establish early whether your site can demonstrate replacement parking. It is a much easier conversation before drawings exist.

What the building bye-laws will require

A garage is not built to habitable standards. Converting it means bringing it up to them, and this is where the real cost sits.

The floor. Garage slabs are commonly laid without a damp-proof membrane and without insulation, and often fall towards the door for drainage. Expect to need a new insulated, damp-proofed floor build-up — which raises the floor level and has to meet the existing house floor sensibly.

The walls. Many garages are single-skin blockwork, which is neither weathertight to habitable standard nor insulated. Expect insulated lining, or rebuilding.

The garage door opening. Filling it needs a proper wall on adequate foundations. The existing foundation under a garage door threshold is frequently not sufficient for a loadbearing wall above, so underpinning or a new foundation may be needed. This is a structural item, not a cosmetic one.

Damp. Garages are unheated and often show damp that nobody minded when it was storing a lawnmower.

Insulation and heating. Thermal performance to current standards, plus extending the heating system.

Ventilation and drainage. Particularly where the conversion creates a bathroom, utility or kitchen.

The room you end up with

Different end uses raise different issues:

• Living room or dining room — usually the simplest. See garage to living room.
• Bedroom — adds escape window and fire requirements. See garage to bedroom.
• Home office — straightforward, and often the best value. See garden and home offices.
• Annexe with kitchen and bathroom — the most complex, and likely a change of use.

Detached garages behave differently from integral ones: see detached garage conversions and attached.

Budget for the structure, not the decoration

The common budgeting error is pricing a garage conversion as a decorating job — plasterboard, flooring, a window. The real cost is in the floor build-up, the wall insulation, and the foundation and lintel work at the old door opening. Those are not visible in the finished room, and they are most of the money.

Drawings detailed enough to show all of it are what let a builder price it honestly. See bye-law drawings for alterations.

Find out where you stand

Book a free consultation. We will look at the slab, the walls, the opening and the parking position, and tell you what the conversion genuinely involves before you commit.