How to Choose a Garage Conversion Specialist in Sussex: Floor, Damp and Insulation

If you are choosing a garage conversion specialist in Sussex, compare how each contractor deals with the hidden floor, damp, insulation, structure and services before you compare the finish or total price.

A garage conversion succeeds or fails in the hidden build-up. Treat it as creating habitable construction from a cold utility shell, not as a decorating job with the garage door blocked up.

The key decisions are usually hidden: floor build-up, damp protection, insulation, ventilation, structure, drainage and the relationship with the existing house.

Start with the room's purpose

Decide whether the converted space will be:

• office;
• bedroom;
• playroom;
• utility;
• living room;
• shower room;
• annexe component.

The use affects:

• heating;
• ventilation;
• plumbing;
• fire safety;
• sound;
• privacy;
• electrical layout.

Do not ask for a generic “garage conversion” quote before deciding what the room needs to do.

Check the existing floor

Garage slabs can sit lower than the house floor.

Ask how the design handles:

• level difference;
• damp protection;
• insulation;
• final floor;
• thresholds;
• existing cracks.

A timber frame and laminate laid straight onto an unsuitable cold slab is not a proper floor upgrade.

The build-up needs to work physically and thermally.

Damp and external ground levels matter

Look at:

• outside paving;
• driveway level;
• door threshold;
• wall damp-proof course;
• water staining;
• gutters/downpipes.

If the garage has been allowed to behave like an unheated utility space, moisture issues may become more noticeable once it is insulated and heated.

Fix water ingress before hiding walls behind new linings.

External walls may need upgrading

Depending on the garage construction, walls may be:

• cavity masonry;
• solid masonry;
• single skin;
• timber frame.

Ask how the contractor intends to achieve the required thermal and moisture performance.

If an internal insulated lining is proposed, understand how much room width will be lost.

For a narrow garage, centimetres matter.

The garage door opening needs a proper wall design

Replacing the vehicle door often involves:

• new wall;
• window;
• damp detailing;
• insulation;
• external finish;
• internal plastering.

Ask how the new infill ties into the existing structure and how the exterior will match.

A front-facing conversion can affect the appearance of the house, so planning considerations should be checked rather than assumed.

Planning and Building Regulations are separate

Planning Portal currently says a garage conversion generally does not need planning permission where the work is internal and does not enlarge the building, but there are important exceptions and restrictions.

Permitted development rights may have been removed or limited, particularly on some developments or protected properties.

Separately, converting a garage into habitable space will normally require Building Regulations approval.

Ask who handles:

• planning check/application if needed;
• building control;
• drawings;
• structural details.

Windows and ventilation

A new room needs appropriate ventilation and daylight for its intended use.

Discuss:

• window size/location;
• opening;
• trickle/background ventilation where required;
• extract ventilation for wet rooms;
• overheating;
• privacy.

If a new opening is being created in a structural wall, that is more than a window-fitting job.

Services should be designed before plasterboard

Agree:

• sockets;
• lighting;
• heating;
• data;
• radiators/underfloor heating;
• plumbing;
• drainage.

Bathroom or utility conversions can become expensive if drainage routes are discovered after the floor is complete.

Electrical work should follow the relevant Building Regulations route; current GOV.UK guidance allows certain work to be self-certified by registered competent-person scheme installers.

Fire safety and the existing house

The exact requirements depend on layout and use.

Tell the designer/contractor if the conversion changes:

• escape route;
• access from hall;
• garage connection;
• bedroom provision;
• internal doors.

Do not treat fire safety as a certificate to find at the end.

What does the quote include?

A complete quote may cover:

• design/approvals;
• strip-out;
• door removal;
• floor;
• damp work;
• wall/roof insulation;
• new infill wall/window;
• electrics;
• heating;
• plumbing;
• plastering;
• carpentry;
• decoration;
• flooring;
• external making good.

Compare the handover state.

A cheap shell conversion can become expensive once every finish is added as a variation.

Landlords: be clear whether it remains one dwelling

Converting a garage into a room within an existing rental is different from creating a separate self-contained dwelling.

Planning Portal specifically warns that conversion into a separate house may require planning permission regardless of how minor the physical work appears.

If the goal is independent accommodation, get planning/design advice before construction.

Write a brief that exposes the hidden work

You can browse garage-conversion specialists across Sussex or post the project.

A useful brief might say:

“Integral single garage in Horsham. Want insulated home office connected to hallway. Garage floor about 120mm below house; no visible damp, consumer unit nearby. Need garage-door infill with window, heating, electrics, Building Regulations and full decoration priced.”

That gives specialists a real conversion scope.

What a complete garage-conversion decision includes

Confirm:

• room use;
• floor;
• damp;
• walls/roof;
• garage-door opening;
• planning check;
• building control;
• ventilation;
• services;
• fire-safety implications;
• final finishes.

The quality of a garage conversion is mostly decided before the plasterboard goes on.

Those are the points that help you distinguish a complete conversion proposal from a quote that mainly prices the visible room.