How to Determine the Cost per Square Foot of Building a Garage

Inside of a garage
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Almost every contractor has a story about a customer calling and asking, “How much will it cost to build a 24 x 24-foot garage?” A contractor has to answer this question carefully because actual construction cost for two identically sized garages can easily vary by $10,000 or more depending on how the client wants to build and finish it. Cost estimates must include detailed questions and answers in order to determine the actual construction costs.

To determine the construction cost for your new garage, the contractor will consider several elements.

Size

Unfortunately, there isn't a 'garage menu' that says small, medium, and large garages each have set price points. A homeowner has so many options to consider that a rough quote over the phone won’t be accurate. That being said, there are some standard sizes and construction costs that contractors rely on when bidding on a garage project. A one-car garage is typically at least 12 x 20 feet in size, while the minimum size for a two-car garage is 20 x 20 feet. These dimensions are considered bare minimums, and the recommendation is usually to build a garage bigger is practical in order to maximize storage space and provide plenty of room for opening car doors. Most homeowners find that a 24 x 24-foot garage provides the best performance for a typical two-car garage, provided the construction site allows enough space.

All builders have a basic per-square-foot cost which they to factor the most basic framing and construction work. While this can vary somewhat from region to region depending on local labor costs, a good rule of thumb is to use the national average of $40 per square foot for a garage that is being added onto the side of your home so it shares common walls, or $70 per square foot if the garage is being built from scratch. For a detached 20 x 20-foot new garage, plan on roughly $28,000 dollars which will include a basic slab concrete foundation, framed walls and roof, and standard asphalt shingle roofing.

This is only a starting point, though, as there are a number of factors that can add to this basic construction cost.

Foundation

When determining the cost per square foot of a garage, it's best to work from the ground up. The first cost you'll need to estimate is the foundation of the unit, which is determined by what climate you live in. In areas where the ground doesn't freeze, homeowners can get away with building their garages on a concrete slab poured right on grade. In parts of the country where frost permeates, it's probably a better idea to have a foundation with a footer below the frost line, with the slab poured between the outer concrete walls that extend downward for stability. Average national cost for a basic free-floating slab is about $4 per square foot, and if outer stem wall foundations are used, the price rises to about $5 per square foot.

In our example of a 20 x 20-foot garage, a new foundation will cost between $1600 and $2000. This cost can vary somewhat depending on the circumstances. For example, if major excavation is required, costs can be higher. Or if the new garage is being built on the site of an old garage with a solid existing foundation, costs could be lower.

Number of Garage Doors

Most of the time you'll need to bring in a company that specializes in installing overhead garage doors, as a majority of contractors don't want a headache and dangers that come with installing the tension springs. This means you'll be paying extra labor costs in addition to the actual purchase of the doors. Garage doors themselves come with options such as windows, insulation, paint color, etc. Obviously, the fancier the garage doors, the more you should expect to pay. The low side of a garage door is around $500, while an insulated or wood door with windows can cost upwards of $2,500 for the door plus installation. Plan on doubling that cost if you are installing two doors in a double garage. This cost does not include the garage door opener or any electrical wiring that must be done.

Windows and Side Entry Door

In bigger garages where you'll have space to work, windows are a nice addition to let in some light and get a natural breeze flowing. Of course, the number of windows you install will also increase the overall cost of your project. The good thing about garage windows is that they're more functional than stylish, so you can buy a less expensive type than you would for a living room or bedroom. Your garage will also need a side entry door, which is mandated by code in most areas.

Standard single windows average about $300 each, and there is usually no extra labor cost since the installation is included in the basic carpentry framing work. A simple side entry door made from flat steel averages about $300, with labor already included in the basic construction costs. You will pay more for more elaborate doors with glass panes, decorative panels, or fiberglass construction.

Some folks don't like the weak link to a theft that a garage window provides and opt for skylights instead. If you choose skylights, expect to add about $125 in time and materials for each cutout.

Type of Siding and Roofing

One of the least expensive garage finishes leaves the property covered in Tyvek home wrap. That's usually because a homeowner ran out of money or a contractor skipped town. But most people will want a more stylish exterior such as:

  • Vinyl siding is inexpensive, easy to install, with plenty of color assortments and long warranties. Nationally, vinyl siding averages about $4 per square foot, installed.
  • Aluminum siding is more durable, can be seamless, and it can be painted. Average costs, installed, are $3 to $8 per square foot, with steel siding somewhat more expensive than aluminum.
  • Fiber-cement siding has become very popular thanks to its unique look and durability (often carrying 50-year warranties). It can be painted and is impervious to heat and cold. This siding is available in both plank and shake/shingle forms. Average national costs are about $10 per square foot, installed. Shake/shingle types are somewhat more expensive than plank types. Though somewhat expensive initially, this is one of the very best and longest-lasting siding materials you can choose.
  • Cedar siding is aesthetically pleasing and environmentally sustainable and has decent thermal insulating properties. Available in both siding planks and shakes or shingles, cedar siding was once the standard for a home with painted siding. Shakes and shingles are sometimes left unfinished. National averages run about $3 to $4 per square foot for siding planks, installed, and sometimes double that for shakes or shingles. Remember, though, that cedar is a high-maintenance siding material and its lifespan averages about 20 years.
  • Stucco is a very durable siding material, and it may be preferable if your home is sided with stucco. Nationally, averages run from $6 to $9 per square foot for stucco siding. Properly maintained, stucco siding can last as long as the garage itself.
  • Brick siding is generally constructed by applying a brick facade against a standard wood-sheathed wall. It is most commonly used on garages in order to match a home that uses brick. Average costs for installation run from $6 to $9 per square foot. Properly maintained, this is another very long-lived siding material.

Roofing surfaces are prices according to squares—a unit of measure that equals a 10 x 10-foot surface. Therefore, if you have a 600 square foot garage roof you actually need 6 squares. Nation averages are $80 to $100 per square for asphalt shingles, by far the most common choice for garages. Asphalt shingles are an economical choice, with lifespans that range from 20 to 40 years, depending on the quality of the materials.

Other roofing materials are also available, and are usually selected in order to match whatever roofing is used on the home:

  • Metal roofing: Average costs run between $7 and $14 per square foot (this roofing is not usually measured in squares). Although expensive, these roofs are very durable, with lifespans of 75 years quite common.
  • Tile roofing: Average costs are between $700 and $800 per square. Although expensive, these roofs are very durable. They may, however, require extra framing reinforcement to support the substantial weight.

Additional Costs

One final option you need to decide on when determining the cost per square foot of a garage is whether you want to finish the inside walls right away. Depending on the R-factor you choose, you'll need to add between $0.50 and $3.00 per square foot for insulation, then drywall, sanding, and painting will add about another $2.00 per square foot. Luckily, this kind of finishing work is fairly easy for DIYers, and many choose to wait to complete this work later.

There are also the costs of wiring and plumbing to consider. Most code areas require at least one basic electrical circuit to power lights, outlet, and the garage door opener, and you may well want to make the electrical service more full-featured. Plumbing is not required, but you may want to include a utility sink with a water supply and drain lines.

Bottom Line

As you can see, calling up the contractor and asking how much a garage will cost is more complicated than you think, and it can bring a number of questions. Be prepared to spend some time identifying the type of garage you want and its features. A new garage can easily cost $50,000 or more, but a healthy investment in your garage can create just the practical sanctuary you want—not just a place to store cars, but a place to fiddle with tools, hang out with neighbors or develop gardening skills. A nice garage will also be a strong positive if you someday decide to sell your home.