How to Build a Garage: Save Thousands Building a DIY Garage Vs Hiring a Contractor

Learning how to build a garage isn’t as daunting as you might expect, well, at least for detached structures. Homeowners who build their own garage can save thousands of dollars instead of hiring a builder who, in many cases, will subcontract to the same construction crews that you can hire. Or if you’re feeling adventurous, or just thrifty, you can invite friends over for a few beers over the weekend and put them to work.

There are many elements to consider at the initial planning stage, such as:

Garage Size: Garages for one, two or even three cars can be designed in various sizes, but the lot and the owner’s budget are usually the limiting factors. Local building codes vary, but generally a structure must not encroach within eight feet of the property line in rural areas and zero to four feet in city limits. Detached garages must also be separated from other buildings by a minimum of eight feet, but this should be confirmed with your local building offices as bodies vary. An important consideration is the roof overhang. Eave and gable overhangs are typically 12″ to 24″ (although less than 12″ is common in windy areas) and should be considered when determining building size and location.

One method of determining the perfect size is to add 12′ to 15′ of width for each vehicle. If you plan to use the inside walls on the sides for storage, you’ll need another two feet of width per side. Length should be a minimum of 22′ and add four to ten feet for a workbench and storage. A two car garage could be calculated as 2 x 12′ +4′ for storage along each wall = 28′ x 22′ long without a workbench. Common sizes include:

1. One Car: Common garage sizes include 12′ x 24′, 14′ x 24′, and 16′ x 24′. A twenty four foot length is pretty much the bare minimum if you have a full size truck and even a small or mid size because there will be little wiggle room at twenty or twenty two feet.

2. Two Cars: The most common garage size in many states and provinces is 24′ x 24′ because many building codes require an engineering design and two inspections by a structural engineer for floating concrete slabs (monolithic) larger than this size. If space is at a premium and both cars are small to midsize, a 20-foot-wide one may be adequate, but certainly not comfortable.

3. Three Car – There are many sizes of three-car garages because there is more space for numerous layouts and homeowners often have larger budgets when considering these larger construction projects. Common sizes are 36′ – 42′ wide by 26′ – 30′ long.

Foundation: Floating slab (monolithic) and slab with frozen wall are the two most common foundation options. Floating slab is less expensive and easier to construct, but often requires engineering design and two inspections for larger concrete slabs (ie, 24′ x 24′). In cold climates, many contractors install 2.5″ foundation foam below the concrete to reduce uplift during freeze/thaw events. Floating slabs designed in cold climates typically require this with an additional two feet of extension around the perimeter of the slab.

Adding 6′ x 6′ #10 wire mesh to the slab is an economical method of increasing the strength of the floor and reducing cracking of the concrete. Most contractors install floating slabs with a 12″ to 16″ thick thickened concrete perimeter around the outside 16″ to 24″ of the perimeter. Adding two rows of #4 rebar will increase the edges. Concrete strength should be a minimum of 3,000 psi and many contractors use 4,000 and 4,500 psi as the additional cost is minimal. Another consideration is to order concrete with fiber mesh and macrosynthetic fiber used for secondary reinforcement of the concrete. Local concrete suppliers can provide costs to add this to the concrete. The thickness of the slab depends on the strength of the concrete and reinforcement designs, however a good rule of thumb is to pour a slab that is 4″ or thicker.

Frostwall’s minimum depth is determined by local building codes and is typically 48″ in cold climates and 36″ in more moderate areas. Once the trench is excavated, a base approximately 12″ wide by 8″ thick is formed and poured and a keyway is etched along the base to prevent movement of the concrete wall. The frost wall is formed and poured on top of the foundation and anchor bolts are installed to hold the walls to the foundation. The concrete slab is then poured to the designed thickness. Obviously, this foundation system requires more time and expense.

Wall Construction – If the garage is to be insulated now or possibly in the future, the size of the wall studs is important, as 2″ x 6″ studs allow for more insulation that may meet building code requirements (for garages with apartments) than 2″ x 4″ studs. Of course, the 2″ x 6″ studs are stronger, resulting in a more structurally sound building.

Wall Height: Walls are generally 8′, but 9′ and 10′ walls are common. In downtown areas, there is often a height restriction on structures such as less than 16′ to the peak of the roof based on the average height from all four corners being measured at grade. This means you can get a bit more height if the garage is located on a bank with a concrete curb or retaining wall at this end and backfilling to the top of the retaining wall. Another method to maximize height in these areas is to pour a 12″ concrete curb around the perimeter of the concrete slab and fill with soil to the top of the curb and grade away from the structure. This method can gain 12″ in height while still meeting height restrictions (confirm this with local building offices before implementing this strategy).

Garage Door Location: Garage doors can be on the gable or on the eaves. Some things to consider:

1. The layout of the existing house may dictate the direction of the roof line. One way to help visualize this is to take a picture of the house and include the area where the garage will be built. Print two copies of the image and hand draw in the garage using the gable and eave options.

2. If the garage is to be built in a cold climate, gabled garage doors are a better design, as snow and ice will slide off the eave.

3. Flexibility with gabled garage doors allows for height for a future carport.

Roof style – Often the style of the roof is dictated by the existing house, for example, if the house has a hipped roof, this would be a good option for the garage. If this is a DIY project and the homeowner is building the garage, it should be noted that a hipped roof is more difficult to build than installing standard trusses. The slope of the roof must also be considered and often needs to match the existing home. A roof slope less than 4/12 (raises 4″ for every 12″ of run or length) is not recommended due to the increased likelihood of water leakage. Higher pitched roofs with certain beam designs can allow for storage, lofts, or even apartments above the main level. The most common roof trusses for garage roof design include:

1. Standard Fink: This is the most common residential truss.

2. Double fink – designed to handle heavy weight loads for higher snow load requirements.

3. Attic – Common for designs that allow storage above the main floor. Access may be by stairs or pull down attic ladders and the available option may be dictated by local building codes.

4. Scissor: This option provides cathedral (vault) ceilings that provide more interior ceiling height. For example, a 24′ x 24′ garage with an 8/12 slope might have a ceiling height of 12′ at the center and 8′ at the wall. This system is generally weighted against construction with regular fink trusses and taller walls.

If this is a DIY garage project, don’t forget to order two gable trusses for each end of the gable. Otherwise, two regular trusses will require wood filler to join the siding and siding (not to mention, the building inspector may not pass the framing inspection). If you are insulating the ceiling, consider ordering “raised heel” trusses to allow adequate insulation between the wall top plate and the ceiling sheathing. This is the only way to meet many attic insulation level (ie R40) requirements.

Garage Plans – Once decisions are made on the above items, it’s time to get your garage plans for your building permit application and builder. It’s important to get good quality garage plans that are easy to follow, accurate, and provide a bill of materials (ok, a bill of materials isn’t important, but it will certainly save a lot of time). There are several websites offering garage plans created by dozens and hundreds of different companies, so consistency and quality control are something to keep in mind. There are a couple of companies that do their own writing in-house and an internet search should turn up these companies. Another option is to hire a local draftsman to create the garage plans.

Lot Plan (Plan): The Building Compliance Department will require a drawing showing (Site Plan) the lot with existing structures, proposed structure, and property lines with measurements indicating distances between property lines and structures. This can be a hand-drawn diagram of a marked copy of the plot/plat plan. The building department may require a survey to confirm the accuracy of the measurements for precise garage location requirements.

Building Permit – Make an appointment to meet with a building inspector to discuss the project and submit the garage plans, bill of materials and site plan to the building department. A building permit may be issued at this time or the building inspector will require a few days to a couple of weeks to review the documents.

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