Extending an Existing Garage: How to Add a 3rd Bay or Extend Depth

To extend an existing garage, you can add a third bay horizontally or extend the depth by 20 feet, but it requires tying the new foundation to the old one and engineering the roof and load-bearing walls.
You also need to check front yard setbacks so the extension doesn’t push the garage too close to the street.

Why Garage Space is at a Premium Along the Wasatch Front

For growing families and outdoor enthusiasts along the Wasatch Front, garage space is at a premium. You may need to:

• accommodate a new driver’s vehicle.
• store a boat.
• set up a dedicated home workshop.

A standard two-car layout can quickly feel restrictive. When your current footprint no longer fits your lifestyle, you face a choice:

• build a completely new detached structure, or
• expand the garage you already have.

For homeowners in established neighborhoods in Sandy, South Jordan, and Draper, extending an attached garage is often the most cohesive way to maximize property value.

But pushing a garage forward by 20 feet or adding a third bay is a major structural project. You need to handle:

• engineering logistics,
• matching architectural profiles, and
• municipal rules.

The Concrete Challenge: Tie-In for Existing Slabs

The foundation is the most critical part of any garage extension. You cannot simply pour new concrete next to an old slab and frame on top of it. The new and old foundations must be structurally integrated to prevent independent settling.

Traditional Slabs vs. Post-Tension Concrete

Many modern homes in Utah are built with post-tension slabs—concrete with high-strength steel cables stressed under tension. If your garage has a post-tension slab, it will be clearly stamped in the concrete.

These cables cannot be cut, drilled, or cored. Damaging a post-tension cable can cause it to snap violently and compromise your entire home’s foundation.

What this means for your garage:
If you have a post-tension slab, you must work with an engineer who knows how to tie in a new foundation without damaging the cables.

The Doweling Method

For standard reinforced concrete slabs, your team needs a proper structural tie-in:

• drill into the existing foundation edge,
• insert heavy steel rebar dowels,
• then pour the new foundation around these dowels to lock the two slabs together.

Excavating New Footings

Even if the interior floor is just a flat slab, the new exterior walls of your 20-foot extension or third bay must rest on continuous, steel-reinforced concrete footings buried at least 30 inches deep to get below Utah’s frost line.

What this means for your garage:
A garage extension needs a proper foundation, not just a surface slab next to the old one.

Roof Engineering: Seamless Profiles and Load Paths

Extending a garage front or adding a third bay changes your home’s roof dynamics. The goal is an extension that looks like it was part of the original design, not a mismatched add-on.

Extending the Front Profile

When extending a garage forward (for example, a 20×20-foot front extension), the existing roof trusses cannot simply be stretched. The framing team must:

• build a new roof system that ties into the existing ridge line and slopes,
• strip away part of the original shingles,
• expose the sheathing,
• and build a structural valley or extension tie-in.

Custom-bent metal flashing and high-performance ice and water shields are essential to protect the seam from heavy snow loads in Sandy and lower-mountain benches.

Adding a Third Bay

Adding a third bay horizontally is a major structural change. The existing exterior side wall of your garage is almost certainly load-bearing, holding up part of your roof.

To open that wall and connect the old garage to the new third bay, your builder must install:

• a heavy, engineered LVL header, or
• a structural steel beam,

across the entire span to safely transfer roof loads down to the new foundation footings.

What this means for your garage:
You can’t just remove a side wall and add a bay. The opening needs engineered support to carry the roof.

Architectural Continuity: Matching Brick, Stucco, and Siding

A successful garage extension must match the rest of your home visually.

Matching materials that have been exposed to Utah’s high-altitude UV and weather for years is challenging.

Siding and Stucco Transitions

• With engineered siding, sourcing the exact profile is easy, but color may differ due to weathering. Professional paint blending across the transition is needed.
• For stucco, matching the texture (fine float vs. heavy lace) requires an experienced mason to avoid a visible seam.

The Brick Challenge

For homes with all-brick or brick-accented facades—common in older Draper and Sandy homes—matching original masonry is complex. Specific brick batches from decades ago are rarely available, so builders must:

• source regional alternatives that match size and color, and
• blend new mortar to mirror the aged look of the existing house.

What this means for your home:
A garage extension should look like part of the original house, not a mismatched add-on.

Balancing Municipal Rules: Front Yard Setbacks

Before breaking ground, your extension design must comply with local zoning rules. Every municipality along the Wasatch Front enforces strict front yard setback rules—the minimum distance a structure must sit from the property line or street curb.

In many residential zones in Sandy City, the standard minimum front yard setback for an attached garage is 20 to 25 feet.

• If your garage sits 45 feet from the street, you have room for a 20-foot front extension.
• If your home is closer to the setback limit, pushing the garage forward 20 feet could violate code and stop the project.

In tight configurations, adding width (a third bay) is often more viable than extending forward toward the street.

What this means for your project:
You must check setbacks first. A 20-foot front extension may not be allowed if your garage is already close to the limit.