Garage conversion cost dataset

Against building the same room

Both figures come from models on this site at the same national wage data, on the same floor area, which is the only reason they can be subtracted from each other — see our room addition dataset. The whole gap is the shell: a garage already has a foundation, four walls and a roof. ⚠️ What the addition buys for that difference is not in this table and it is the real comparison — you still have a garage afterwards. In most American markets a house without one sells to a smaller pool of buyers, and it is declared in the exclusions because it is a judgement about your street rather than a number we can publish.

The slab, and the change of use

⚠️ A garage slab falls towards the door so that water runs out, and it sits a few inches below the house floor so that petrol vapour cannot flow inwards. Both are correct in a garage and both are a problem in a bedroom, and fixing them is a floor rather than a levelling compound — which costs three or four inches of headroom on top of the 8.5 feet a garage typically has. The right-hand table is what stops this being a decorating job: it is a change of use, and that brings current insulation requirements, an escape window for a bedroom, and rules about any gas appliance that stays in the space.

Single, double, or bigger

A single garage is around 240 square feet and a double around 400, with a door opening of nine and sixteen feet respectively — and the door opening is a real driver, because closing it up is framing, a window, insulation and cladding that has to match the house. The perimeter is derived from the area assuming a plan roughly 80 feet around, which is declared rather than measured. ⚠️ Matching the outside is what decides whether the house reads as a converted garage forever: siding fades and brick weathers, so the right product is still the wrong colour, and it shows exactly where a buyer looks first.

Line items

67% of the reference total comes from estimated rather than official figures. The reference job is a 400 square foot double garage with a 16 foot door opening, converted to a living room: a new insulated floor over the slab, the door opening closed up, insulated and boarded to current code, and the heating extended — 185.8 trade hours.

The reasoning behind each figure

Drawings and the change-of-use permitestimated, ±60%

• ⚠️ A garage conversion is a change of use rather than a repair, and that is the single most important sentence on this page. It is what brings in the current insulation requirements, the escape window if it becomes a bedroom, and the inspections — and it is why «we can just board it out» is a quote for a different, unpermitted job.
• Doing it without a permit is cheaper until the house is sold, at which point unpermitted living space is a problem for a buyer, a lender and an insurer at the same time.
• The permit fee itself is not in this dataset: it varies by an order of magnitude between jurisdictions and there is no national figure to average honestly.

Stripping out and protecting the rest of the house

• Modelled at 0.05 hours per square foot, multiplied by 1.3 in a house built before 1978 where disturbing painted surface brings the work inside the federal lead programme.
• Clearing the garage, taking out whatever shelving and racking is fixed to the walls, and dust protection at the door into the house.

New insulated floor built over the slabestimated, ±36%

• Treated sleepers shimmed to a level plane, rigid insulation between them, a vapour retarder and a subfloor over the lot.
• ⚠️ This exists because a garage slab is built wrong for a room on purpose: it falls towards the door so that water runs out, and it usually sits a few inches below the house floor so that petrol vapour cannot flow inwards. Both are correct in a garage and both are a problem in a bedroom.
• The band is the depth of build-up needed, which depends on how much fall there is to take out.

New insulated floor built over the slab — labour

• Modelled at 0.055 hours per square foot. Most of it is the shimming: every sleeper is packed to a line rather than laid on the slab, because the slab is not flat.

Self-levelling screed over the slabestimated, ±43%

• A poured screed that takes the fall out of the slab without raising the floor much. It keeps headroom, which is its whole argument.
• ⚠️ It does nothing about the cold. A slab sitting on the ground is a heat sink whatever is stuck to the top of it, so this is a reasonable floor under tile in a utility room and a poor one under a bedroom.

Self-levelling screed over the slab — labour

• Modelled at 0.03 hours per square foot: preparing and priming the slab, then mixing and pouring to a level.

Closing the garage door opening: framing, window and claddingestimated, ±46%

• Priced per linear foot of the old door opening. Framing the infill wall under the existing header, sheathing, a window or a door, insulation, and cladding the outside to match the house.
• ⚠️ Matching the outside is the part that decides whether the house reads as a converted garage forever. Siding fades and brick weathers, so an infill panel that is the right product is still the wrong colour — and where it shows most is exactly where a buyer looks first.
• Taking the door, the tracks and the opener out is included. So is the reality that the opener is now scrap.

Closing the garage door opening — labour

• Modelled at 1.35 hours per linear foot of opening, which covers removing the door and its gear, framing, sheathing, setting the window and cladding.

Insulating the walls and the ceiling to current codeestimated, ±43%

• ⚠️ This is the line the change of use brings with it. A garage is unconditioned space and its walls are usually bare; the moment it becomes a room it has to meet the energy code where you live, which is a real specification with a real inspection rather than «put some insulation in».
• Priced across the wall and ceiling area together. The band is batts at the bottom and dense-pack or foam at the top, which is what a wall with no easy access needs.
• The ceiling matters as much as the walls here: above a garage is usually either an unheated attic or nothing at all.

Insulating the walls and the ceiling to current code — labour

• Modelled at 0.02 hours per square foot insulated and air sealed.

Plasterboard, taped and finishedestimated, ±33%

• Board, tape and compound across walls and ceiling. Many garages already have board on the wall shared with the house, and it is rarely finished to a standard anybody would live with.

Plasterboard, taped and finished — labour

• Modelled at 0.032 hours per square foot, hanging and finishing.

Flooring, trim and decorationestimated, ±45%

• Floor covering, skirting and casing, an interior door where the garage door into the house used to be, and paint.
• That interior door is worth a note: it was a fire-rated, self-closing door because it opened into a garage. Once the garage is a room it is an ordinary door — and if the conversion leaves any part of the space as a garage, it has to stay what it was.

Flooring, trim and decoration — labour

• Modelled at 0.085 hours per square foot of floor, finishes and decoration.

Rewiring it as a room rather than a garageestimated, ±39%

• A garage typically has one circuit, a couple of outlets and a bulb. A habitable room needs outlets at code spacing, lighting on its own switching, and interconnected smoke and carbon monoxide alarms.
• ⚠️ Adding a bedroom usually means the alarms in the rest of the house have to be brought up to current requirements as well, not just the new room. That is a whole-house item arriving with a one-room project, and it surprises people.

Rewiring it as a room rather than a garage — labour

• Modelled at 0.05 hours per square foot, first and second fix together.

Escape window cut through the exterior wallestimated, ±49%

• ⚠️ Required in any room used for sleeping, and it is the line that makes bedroom conversions fail inspection when a quote was written as boarding and painting.
• Cutting a new opening through what is often masonry or a braced framed wall, installing a lintel or header, and fitting a window that meets the minimum opening size and sill height — an ordinary window of the same rough size does not necessarily qualify.
• The band is a framed wall at the bottom and a masonry or brick-veneer wall needing a structural lintel at the top.

Escape window cut through the exterior wall — labour

• Modelled at 16 hours: needling and propping, cutting the opening, setting the lintel, fitting and flashing the window, and making good inside and out.

Saw-cutting and breaking out the slab for the bathroom drainestimated, ±43%

• ⚠️ This is what makes a bathroom in a garage different from a bathroom anywhere else in the house. Upstairs a drain runs between joists; here it runs *inside the concrete*, so the slab is saw-cut, broken out, dug, the pipe laid to fall, and then the trench is backfilled and re-concreted.
• Modelled at 22 linear feet of trench, which is a run from a bathroom in the corner of a garage out to where the house drain leaves. It is declared rather than measured, and the real length is whatever the survey finds.
• Cutting cured concrete releases respirable crystalline silica, so it is wet-cut or done with extraction — the same requirement as any other concrete cutting on this site.
• The band is a straightforward cut across a plain slab at the bottom and a thicker or reinforced slab needing more breaking at the top.

Saw-cutting and breaking out the slab for the bathroom drain — labour

• Modelled at 1.1 hours per linear foot of trench: cutting, breaking, barrowing the spoil out, then backfilling and re-concreting after the pipe is in and inspected.

Partitioning the bathroom off inside the conversionestimated, ±53%

• Stud partitions, a door, the extra board and finishing, and the extract fan and its duct to outside — which is not optional in a room with a shower in it and is the item most often left out.
• ⚠️ What is NOT in this line is the bathroom itself: fixtures, tiling, the supply pipework and the fit-out. Our bathroom addition calculator prices all of that, and it is a large number rather than a rounding error on this one. Adding the two together is the honest total for a suite.

Partitioning the bathroom off inside the conversion — labour

• Modelled at 15 hours to frame, board, hang the door and run the extract duct.

Extending the existing heating and cooling inestimated, ±57%

• Ducts or pipe run from the existing system, registers, and balancing.
• ⚠️ Same caveat as any addition: extending ducts does not add capacity to the system feeding them. A garage is often the worst-insulated part of the house even after conversion, so it is also the room most likely to be the one that never gets comfortable.

Extending the existing heating and cooling in — labour

• Modelled at 12 hours to run, connect and balance the new branch.

A ductless heat pump for the converted space insteadestimated, ±40%

• One outdoor unit and one head, independent of the rest of the house.
• Often the better answer in a garage rather than the fallback: the space has its own thermal behaviour, it can be shut off when nobody is using it, and it does not load a system that was sized before this room existed.

A ductless heat pump for the converted space instead — labour

• Modelled at 11 hours to mount, run the line set, evacuate and commission.

Dealing with a gas appliance left in the spaceestimated, ±60%

• ⚠️ A water heater or furnace that lived happily in a garage is in a different situation once the garage is a bedroom. Combustion appliances in or beside sleeping space are tightly restricted, and the usual outcomes are enclosing the appliance in a sealed, separately ventilated cupboard, moving it, or replacing it with a sealed-combustion or electric unit.
• The band covers enclosing and venting at the bottom and relocating at the top. Replacing it outright is a different job — our water heater and furnace calculators price that.
• Carbon monoxide is the reason all of this exists, and it is not a formality: the CDC publishes what exposure does and why alarms matter.

Dealing with a gas appliance left in the space — labour

• Modelled at 10 hours to enclose, vent and re-commission, or to relocate.

Relocating the laundry, the water heater or the panelestimated, ±60%

• A garage is where a lot of houses keep the washer, the dryer, the water heater and sometimes the electrical panel. All of them can stay in a room in principle; in practice most people want them somewhere else, and moving them means drainage, venting and circuits.
• ⚠️ The panel is the one to check rather than assume. There are restrictions on where a panel can be — clearance in front of it, and not inside a bathroom or a clothes closet — so a panel that was fine on a garage wall may not be fine on a bedroom wall.

Relocating the laundry, the water heater or the panel — labour

• Modelled at 14 hours across the trades involved in moving them.

Not included in this dataset

The permit fee, and whether your area allows it

⚠️ Some jurisdictions restrict garage conversions outright, and many require a minimum number of off-street parking spaces to remain. That is a phone call to the building department, it is free, and it should come before any of this.

Losing the garage

It is the largest cost on this page and it has no dollar figure: the cars go outside, the storage goes somewhere, and a house without a garage sells to a smaller pool of buyers in most American markets. Whether that matters is a judgement about your street rather than a number we can publish.

A service upgrade if the panel is full

The electrical assumes there is room in the existing panel for the new circuits. Where there is not, that is a service upgrade priced on our electrical panel page.

Bathroom drainage

Turning the space into a suite means a new drain run and, where the slab sits below the sewer line, a sewage ejector pump. Our bathroom addition calculator prices that properly, and it is a large number on its own rather than a rounding error on this one.

Damp coming up through the slab

A garage slab often has no vapour barrier under it, because it never needed one. Building a floor over it assumes the slab is dry. If it is not, that is a moisture problem to solve first — sealing or a proper barrier — rather than something to cover with a subfloor.

Re-siding or re-roofing to match

Cladding the infill panel to match is included. Re-cladding a whole elevation because the match is poor is not, and it is priced on our siding page.