The short answer
A loft conversion usually costs more and takes longer, but it adds a whole new floor and is the better choice when you need a proper bedroom or bathroom. A garage conversion is usually the cheaper and quicker job, and it suits you if you want a ground-floor room such as a home office, playroom or guest room. The right choice depends on how much space you need, what your house allows and whether you can live without the garage. The real prices homeowners paid are shown separately on this page, so use them alongside this guide.
How they differ
A loft conversion turns unused roof space into a habitable room. The work often involves strengthening the floor, adding a staircase, insulating the roof and fitting windows. Some lofts need only roof windows and a floor upgrade. Others need a dormer or a larger change to the roof shape to get enough headroom. The result is extra space above the rest of the house, so you do not lose any ground-floor area.
A garage conversion turns an existing, usually attached, garage into a room that is part of the house. The structure is already there, so the work is mostly about the following:
- replacing the garage door with a proper wall and window
- insulating the walls, floor and roof
- making sure the floor is level and damp-proof
- connecting heating and electrics
You gain floor area but lose covered parking and storage.
Both jobs can be affected by planning rules and will almost always involve building regulations. Many loft and garage conversions fall within permitted development, but not all do. Listed buildings, conservation areas and some newer estates with conditions attached to the original planning consent can change the picture. Check with your local council before you commit. If you share a wall with a neighbour, loft work in particular may involve them, so ask your builder about this early.
Cost: what makes each more or less expensive
In general, a garage conversion costs less than a loft conversion, because it makes use of walls, a floor and a roof that already exist. A loft conversion involves more structural work and more trades, and it changes the shape of the building.
What pushes a loft conversion up:
- the type of conversion, with simple roof-light designs usually cheaper than dormers or full roof alterations
- the amount of structural steelwork needed
- adding a bathroom, which means plumbing and drainage
- the staircase, particularly if it takes space from the floor below
- scaffolding and access
- the size of the roof and how much headroom you already have
What pushes a garage conversion up:
- poor or missing damp-proofing in the floor
- a floor that sits lower than the house and needs raising
- the work needed to replace the garage door with a wall that matches the house
- adding a bathroom or kitchen area
- extending heating and wiring a long way from the existing systems
- the quality of finish you want, as a room that has to feel like part of the house costs more than a basic utility space
There is also a cost that does not show up on a quote. Losing a garage may affect how easy your home is to sell, depending on your street and how much parking buyers expect. A loft conversion tends to add more usable space, but a badly done one can feel cramped. Look at the prices homeowners actually paid on this page, and compare like with like: the size of the room, whether a bathroom was included and the type of property.
Lifespan and upkeep
Both conversions should last as long as the rest of the house if they are built properly. What matters is the quality of the work and the materials.
Loft conversions need ongoing attention to the roof, the windows and any flat-roofed dormers, which are the parts most likely to need repair over time. Insulation matters a great deal, because a poorly insulated loft room can be hot in summer and cold in winter. Keep an eye on seals around roof windows and the condition of any flat roof coverings.
Garage conversions need good damp protection and insulation more than anything. If the floor or the new wall is not done correctly, you may notice condensation, cold spots or damp. The new infill wall where the door used to be is the area to check. Otherwise, upkeep is much like any other ground-floor room.
In both cases, keep the paperwork, including building regulations sign-off and any guarantees. You will need them when you sell, and they help if something goes wrong later.
When to choose Loft conversion
A loft conversion is the better choice if:
- you need a full extra bedroom, or a bedroom with an en-suite, and want to keep the ground floor as it is
- you want to keep your garage for parking, storage or a workshop
- your loft has decent headroom and a roof structure that suits conversion
- you want to add the most space and are prepared to pay more for it
- the garage is detached, small or in poor condition and would be awkward to convert
Be realistic about the disruption. A loft conversion takes longer, involves work over your head, and a new staircase will change the layout of the floor below.
When to choose Garage conversion
A garage conversion is the better choice if:
- you want the more affordable route to extra living space
- you do not use the garage for its original purpose, or can store things elsewhere
- you need a ground-floor room, for example for someone with limited mobility, a home office or a children's playroom
- your loft is low, has an awkward roof structure or would need major alterations
- you want less disruption and a shorter build
Think about parking before you start. If you rely on the garage and there is no space for a car on the drive or the street, converting it could cause daily problems and may make the house harder to sell.
Questions to ask a tradesperson
- Does this work need planning permission, or will it fall under permitted development? Who applies if it is needed?
- Will you handle building regulations, and will I get the completion certificate?
- What exactly is included in the quote, and what could change the price?
- For a loft: is my roof suitable, and what will happen to the staircase and the floor below?
- For a garage: how will you deal with the floor level, damp-proofing and insulation?
- How will you match the new wall and windows to the rest of the house?
- Who is responsible for the structural calculations, and have you done similar work nearby?
- What guarantees or insurance cover the work?
- How long will it take, and how will the disruption affect daily life?
- Can I speak to past customers or see finished jobs?
Get more than one written quote, and compare them against the real prices homeowners paid shown on this page. A quote that is much lower than the rest deserves questions, not celebration.