Building a garage bump out addition is an excellent way to create more storage space in your garage to house lawn equipment, bicycles, sporting gear, and even an automobile. While a garage bump out might not be as involved as a full-on garage addition, the project is a big one. However, if you have some advanced DIY skills and a helper or two, building yours may be doable with a little guidance. Here are the steps necessary to complete the project.
Prepping to Build a Garage Bump Out
Photo: Ursula Page / Adobe Stock
Deciding whether or not to install a garage bump out as a DIY project depends on your level of comfort with the tools and processes necessary versus the bump out costs associated with hiring a pro through a renovation contract.
The first thing you'll need in preparation for this project is a site drawing and plan of the property and your bump out proposal. You'll also likely need a detailed construction plan and drawing. The documents will be necessary for obtaining a building permit for the build. The construction can begin once you get your hands on the building permit.
Keep in mind that municipalities, HOAs, and neighborhoods may have their own rules regarding bump-out style garage additions relating to foundation requirements, property-line setbacks, and general construction requirements. Studying the requirements and restrictions for your location before applying for the permit is prudent and can be time-saving.
Build Temporary Roof Support
For this project, you'll need to remove the portion of your existing garage wall in the location of your garage bump out addition. To prepare to create the hole, use two-by-fours to build a temporary support structure for the roof area near your work.
Build a Header
Use a pair of two-by-tens and a two-by-four to build a header wide enough to accommodate your addition, plus the king studs necessary to support the header, as noted in your construction plans. Nail the two-by-tens together flat and nail the two-by-four flat onto the bottom of the header.
Install the Header
To install your header, mark the existing garage wall studs at the top and bottom of the header installation location. Use a reciprocating saw and claw hammer to remove the stud sections and place the header in the space. Support the header by adding king studs to each side and nailing them in place. Toenail the leftover top sections of wall studs into the top of the header. Once secure, you can remove the temporary support structure.
Remove the Wall Section
The space under the header and between the king studs will need removal next. You can remove the exterior siding before doing this step if you wish. Use your reciprocating saw to cut out the wall section, including the studs, and remove the section.
Attach a Ledger Board
To create a floor for your bump out, first, attach a two-by-ten or two-by-eight ledger board extending the width of the addition plus its walls to the garage wall's exterior with its top equal to 3/4 inches below the existing garage floor height. You may have to remove a small amount of siding for this part. Support the ledger with extra lumber material or anchor it to the garage's concrete blocks if possible. You'll come back to anchor it more securely later.
Build the Floor
Use a post-hole digger and concrete to secure treated support posts according to your construction plan for the far side of your bump out. In many municipalities, a frost-depth footing will be necessary at this step. Once your footings and posts are secure, follow the floor-framing plan to build your structure from treated two-by-eights or two-by-tens. Sheath the floor with 3/4-inch treated plywood and fasten it with 2-inch nails and construction adhesive.
Build a Concrete Floor
You may also install your garage bump out onto a concrete slab instead of a wooden floor. For that, set your concrete forms equal to the existing garage floor height and fill them with concrete and reinforcing material if necessary for your location. Allow the slab to cure for at least 24 hours before proceeding with the next steps. Check with your municipality for any additional support requirements.
Secure the Ledger Board
To secure the ledger board and create a smooth walking surface, pour concrete between the ledger board and the garage floor to fill the gap and make them level with each other and smooth with a trowel. Use concrete anchors through the ledger board to firmly secure it to the garage structure after allowing 24 hours for the concrete to cure.
While waiting for the concrete to set, you're free to start the next building step but use caution not to disturb the wet concrete.
Build the Walls
Build each of the three bump out addition walls individually by laying them out and constructing them flat on the new floor before raising them and securing them in place with 3-½-inch nails through the flooring and to each other. Many municipalities will also require fastening your walls with metal clips or fastening plates. Frame your walls to accommodate any windows you choose to install as well.
Frame the Roof
To frame the roof, cut away the garage siding to accommodate the rafters nearest the existing garage wall and fasten them directly to the structure's sheathing. Build the remaining rafters or install roof trusses to speed up the process. Secure the rafters or trusses with nails and hurricane ties, if necessary where you live.
Complete the Roof
Complete the roof by securing 1/2-inch plywood to the top of the rafters with 2-inch sheathing nails and roofing spacers. Install roof flashing, underlayment, and roofing material according to the manufacturer's instructions for the products you're using and in accordance with the local building code.
Install Siding
Install the 1/2-inch wall sheathing plywood and fasten it with 2-inch sheathing nails. Next, install the windows, house wrap underlayment, and siding to match the rest of the garage.
DIY vs. Hiring a Pro
Putting any addition onto your home or garage will always be a huge task. However, an experienced DIYer can complete this project with patience and the help of some friends or family over the course of several days. That said, installing a bump-out addition certainly isn't for every homeowner. The job requires heavy lifting, ladder or scaffolding work, and specialized skills.
Most homeowners choose to hire a local garage remodeling company that can handle everything, including developing the plans and drawings, obtaining permits and ensuring code compliance, digging, constructing, and finishing your project within a couple of days while you sit back and relax.
Frequently Asked Questions
You can extend a garage forward. However, the existing layout and the amount of depth you wish to add will determine how much effort and money the task will require. Considerations include moving the garage door and support structures, rebuilding or adding onto the roof, and extending the garage floor and sometimes the foundation underneath.
Putting an addition on top of a garage is similar to installing a second story on a single-story home. You'll likely need the assistance of a structural engineer, however, to determine if the garage's existing foundation, walls, and ceiling can handle the extra loads. Typically, your garage will require adding strength to one or more of those things to support the addition.
Deane has spent 30+ years in residential construction, contracting, remodeling, maintenance, and home repair, and now contributes DIY and educational articles for publications like Forbes Home and U.S. News. Throughout his career, he has strived to help homeowners find the potential hidden within the walls of every home and empower them to take control of their household repair and remodeling endeavors.
Deane has spent 30+ years in residential construction, contracting, remodeling, maintenance, and home repair, and now contributes DIY and educational articles for publications like Forbes Home and U.S. News. Throughout his career, he has strived to help homeowners find the potential hidden within the walls of every home and empower them to take control of their household repair and remodeling endeavors.
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