Hello Rufus,
Cost per square foot will vary, depending upon;
-where you live
-existing site conditions
-design and permitting
-utility locations
Generally detached garages are more cost effective per square foot.
Wesley
Cape Design Build
Hello. Yes there is a difference. A detached might be less expensive because you do not have to tie into the house.
My answer will apply in Chicagoland area. Northeast Illinois.
Detached garage - we can build on concrete slab. No major electric work, no drywall and insulation will be required. Detach garage 20x24 costs $7,000 to $10,000.
Attached garage will require regular foundation and fire rated drywall. Most people will add insulation, more electrical outlets and light. At this point, there is almost no difference from building home. Just throw epoxy on the concrete slab and you have same cost.
With new home construction, you can start around $30,000 for 20x24 attached garage.
If you want to add to the existing home, the starting price will be $50,000 or more.
The relative difference in cost between the two would be the additional building requirements and fire codes with the attached garage. There will be a need to insulate and drywall the wall that is adjacent to the home (living space).
Great question, Rufus!
- Lot Coverage
You must determine from the Zoning department at the local municipality if a garage addition is allowable on the lot of land. Most communities allow up to 30% of total lot coverage. For instance, if the total square footage for your lot is a quarter-acre (or 10,890 sq. ft.), you are allowed up to 3,267 sq. ft. of ‘covered’ space like concrete, house, deck (usually counted as 60% of square footage - if the deck is 300 sq. ft. then only 180 sq. ft. counts toward the total) - think of anything that is impermeable or has a roof covering. Therefore, if your house is 2,400 sq. ft., your driveway is 400 sq. ft. and your deck accounts for 200 sq. ft., then you will only have 267 sq. ft. remaining to build a garage. However, some zoning departments will allow an additional 1%-2%. But, you need to ask the zoning department first.
- Side Yard
In addition to lot coverage, the zoning department will look at side yard. I can only assume, but, in my experience, total side yard (minus easement) is generally between 15’-20’ in total. In other words, take the closest point of the house to the edge of the property (on both sides) and add the total number of feet. Also, there is typically a minimum of 5’ required on both sides. Therefore, the garage must be built within the side yard requirements of the village.
- Detached
If an attached garage is not feasible, but the detached garage is allowable, then check the requirements for how close the garage can be built to the house. There is typically a requirement such as, “The detached garage must be placed 30’ from the back of the house.” In other words, from the furthest section of the back side of the house to the nearest point of the detached garage must have a 30’ distance.
- Plans
Regardless of whether the garage is attached or detached, you will most likely need plans, especially if the garage is attached. Most architectural plans, for a garage, will be between $1,000-$2,000. The reason is because the attached garage is actually an addition to the home, so there are many aspects to consider such as electrical, HVAC, roofing (tie-in to existing line). An attached garage will also require concrete footings. Concrete footings is essentially a concrete wall (that is about 4’ deep by 1’ wide) that goes around the perimeter of the garage. In other words, this is where the walls would be built. Concrete footings are essential to an attached garage because the garage is becoming part of the overall structure and you do not want the attached garage to shift and to pull away from the house. Concrete footings will add about $5,000 to the cost of the project, if a detached garage does not require concrete footings. Detached garages may not require concrete footings - just use 4,000 psi at 5" depth with wire mesh and a 4" gravel base.
In all, inherently, the attached garage has the propensity to cost more than a detached garage due to the nature of the project. With an attached garage, you are altering and adding to the home’s structure and square footage. So think of the addition from the municipality’s point-of-view - a) if the current homeowner sells the home after the addition, “Is the structure safe?”, b) the property assessment and value, “How much is this home now worth?”, and c) property taxes. Adding to the home’s structure is very important to everyone involved.
But, adding a detached garage is not as involved. If you hire a General Contractor to complete the garage from the ground-up, the total project will probably cost about $15,000. An attached garage will cost more than that. Therefore, you have to determine what is the value in the new garage for you? What is the purpose of the garage? If the garage will be primarily used to store cars, tools, maybe a lawn mower, then select a detached garage. However, if you want the garage to be insulated with HVAC and lights, and you would like to finish the garage with epoxy floors and drywall, then an attached garage might be worth it to you. And finally, if you are anticipating selling your home in the next few years, select a detached garage. Garage projects do not have the return to make the project economically rewarding.
Hopefully this helps answer your question. If you have any more questions, please ask DDT Home Transformations. Thanks again for your great question!