​Beginner's guide to converting a garage into living space

Johannes van Graan Johannes van Graan
homify Modern living room
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What do you use your garage for? Do you really park your car in there? Is it filled with junk and memorabilia you haven’t looked at in nearly 10 years? Then you may want to consider converting that unused space into something practical.

A well-thought out garage conversion can add as much as 10% to the value of your home, and is one of the most cost-effective home improvements to improve your property’s resale value. Who knew, right?

And of course don’t forget the benefit of increased living space without incurring the costs and inconveniences of moving house. 

Sound good? But before you start planning, let’s first take a look at the information you’ll need to carry out that garage conversion.

1. Design and space planning

The typical garage has a longer and thinner build than most rooms. To achieve a more natural shape for the conversion, consider using stud or block walling to convert that long shape into two spaces. The additional (smaller) room can be used as a toilet, shower, or perhaps a storage space. 

Need that expert look? Check out our range of professionals.

2. Planning permission

If you’re not planning on altering the structure of the building for a garage conversion, planning permission is not needed. But if you live in a listed building or a Conservation Area, planning permission may be required for even minor modifications. 

Standalone garages are more likely to require ‘change of use’ planning permission when converted to habitable rooms. Phone up your local planning department to verify this. If the answer is favourable, write the next day and ask for written confirmation.

3. Building regulations

Changing that garage into a habitable room will mean complying with building regulations, including delivery of a building notice to your council. Building regulations apply to ventilation, moisture proofing, insulation, fireproofing, escape routes, and structural soundness. As a result, almost any design decision must take them into account.

Dividing up the garage means a new room is created, which is subject to a set of building regulations that require an escape route and ventilation separate from the main room. 

Bear in mind that the building inspector will also want to visually inspect windows, doors, fireproofing and foundations before he gives a certificate of completion.

4. Insulation and damp proofing

Insulation is assessed in terms of a U value: the measure of the rate of heat escape, in watts, from a square metre of the material in an hour. Walls must achieve a U value of 0.35W/m²/K, and roofs a U value of 0.16W/m²/K if pitched or 0.25 W/m²/K if flat and the floor 0.25W/m²K. Windows should be 0.18 W/m²K. The floor will need to be 0.25W/m²K.

Window manufacturers will give the U value as part of the specification of the windows.

Damp proofing will be necessary in the walls and floor. Many garages will already have a damp proof course in the walls, but make sure to verify this. The floor will need to be damp proofed by laying a damp proof membrane at the same time the floor is remade.

5. Plumbing and wiring

Make a thorough survey of the plumbing and wiring in the house and garage. Locate the main outflows for water and the soil outflow (if you plan to install a toilet).

Check the garage’s walls and ceiling for wiring. Rewiring the garage for lights and electric radiators will place additional strain on the household mains, which might require the installation of a separate consumer unit.

6. Flooring

Although the existing garage floor will be strong enough, it will require additional damp proofing and insulation to meet building regulations.

A concrete floor can be created and a damp proof membrane added between the two layers. Insulation is also added under the new floor, but sometimes requires a separation layer to prevent a chemical reaction with the damp proofing. 

A raised timber floor may also be built over the existing floor, with damp proofing laid under the timber and insulation between the joists and the timbers of the floor. Note, however, that fire regulations may require a step in a raised timber floor at doorways to prevent fire spreading along the floorboards.

7. Walls

External walls are covered by building regulations and must meet requirements in terms of moisture-proofing and insulation. If the garage is integral to the house, the exterior walls will usually meet building regulations. Otherwise consider a second block wall, or a stud wall, inside the existing exterior wall behind which insulation and power- and water lines can be placed. 

Interior walls between rooms will also need to meet building regulations’ requirements for fireproofing. This can mean one or two layers of fireproof plasterboard on stud walls (which is unnecessary for block walls). Please note that doors through interior walls also need to be fireproof, with a 30-minute rating.

8. Windows and doors

A second room in the conversion will require ventilation to meet building regulations, as well as an escape route to meet fire regulations. Building regulations require a window 1/20 the floor area of the room, while fire regulations require a window with a 600 mm base opening and a total area of not less than 0.45 m². The window must also have trickle vents.

Windows that meet these requirements are available in metal frame or uPVC, though metal frame windows must have a ‘thermal break’ (because of metal’s conductivity) to meet insulation requirements. Wood frame windows can meet requirements too, but they have to be of sufficient depth to accommodate a 24 mm double-glazed unit. 

Doors must meet the same requirements as windows in terms of their U value. In addition to uPVC doors with double-glazed windows, wooden doors are also a good choice.

9. A completion certificate

Any project that requires a building notice will require a completion certificate, which is proof that the completed work met regulations. However, having a completion certificate does make a difference to the value added to your property by the garage conversion. Estate agents and prospective purchasers will value your completion certificate highly since things like an under-floor damp proof course can’t be proven without one.

Upon final inspection, be sure to submit to the building inspector the documentation proving that building regulations were met in the construction and installation of the parts he has not visually inspected. 

Once the building inspector is satisfied, the completion certificate should follow, often within 28 days.

10. The pros of a garage conversion

Design control: Converting a garage means every step of the design process is under your control, subject to technical and legal restrictions.

Added value: Converting a garage into a habitable room adds more value to your home than it costs in most cases.

Council tax: Moving from a 3- to a 4-bedroom house could put you up a council tax band. A garage conversion leaves council tax bands unaffected.

11. The cons of a garage conversion

Disruption: During garage conversion, one or more existing rooms will frequently be rendered unusable by building work (adjoining spaces, gardens or yards are most affected). In addition, workmen will also be present in your home during working hours. 

Planning uncertainty: Projects which require planning permission may not receive it. Application will involve a non-returnable fee, usually of about £150. This will be higher if you want to alter a listed building or you live in a conservation area.

Cost uncertainty: Once investigations begin on your property, you might be required to pay for additional improvements or repairs. Damage resulting from building work might require repair, and delays and unpredictable setbacks might elevate costs far beyond budget. 

However, just remember that conversion is likely to remain the cheaper option; moving house usually costs about £10-15k (considerably more in London) in addition to the cost of the new house itself. 

Should you decide to stick with that garage as is, we can help you with: Getting your garage organised in a weekend.

Styling a garage conversion

The sky is truly the limit when it comes to diy garage conversions; with a garage conversion, you've got plenty of options. Taking it step by step is easy with our tips above, but interior design can stump the best of us.

If you're looking to convert your garage into a bedroom, here are our top design tips. And if you're worried about the lack of windows, add some plants (fake ones will do the job just as well).

It would be a great idea to add plenty of lighting to brighten up the dark space. For bedrooms, we recommend bedside table lamps. For living areas or kitchens, going for overhead lighting is best. Make sure to incorporate lighting that looks natural.

How would you style a garage conversion? And if you have any experience converting a garage into a room, give us your best tips.

How would you use a garage conversion?

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