A two-car garage added onto the side of an existing ranch is one of the most common projects we see across Hixson, East Ridge, and Red Bank. It looks simple on paper: dig three new footings, leave the existing wall alone, tie in the framing. In practice, the dig is the part that decides whether the new garage moves with the house or sits independently and cracks at the seam.
The existing house footing is at whatever depth the original builder set. That number is rarely written on a plan that survived to today. Before we open the new trench, we want to know how deep the existing footing actually sits.
There are three ways we figure it out:
Without one of those, you are guessing — and a 6 inch depth mismatch between the new garage footing and the existing house footing is exactly the gap where a crack will form. Differential settlement at the tie-in is the most common failure on an attached garage addition.
The new garage perimeter has to align with the existing wall. We snap a line off the existing foundation, square it, and verify diagonals before any digging happens. A garage that is 1 inch out of square gets ugly fast — overhead doors do not forgive misalignment, and the roof framing on the tie-in gable depends on the new walls being parallel to the existing ones.
We also locate buried utilities along the side of the house before the bucket touches dirt. Sewer laterals, gas service, irrigation, and downspout drains all tend to live where you want to dig.
Excavating a footing 12 inches away from an existing foundation wall takes more care than digging in the middle of a vacant lot. A few things we watch for:
For most garage additions in the metro, the existing house footing sits at 18 to 24 inches. A new garage footing typically matches that depth, sometimes a little deeper if the soil at the existing depth has been disturbed by the original construction.
There are two main strategies, and the excavation differs for each.
Doweled tie-in. The new footing butts up against the existing foundation wall, and rebar dowels are drilled into the existing concrete to mechanically link the two. The dig leaves a clean square edge against the existing wall. The new footing pours tight to the existing surface.
Independent footing with control joint. The new footing sits parallel to but not touching the existing wall, with an intentional gap. This lets the addition move independently. The dig leaves a small clearance against the existing wall, and the gap gets backfilled and detailed for water.
Which approach is right depends on the engineer's call and the size of the addition. Larger additions on different soil conditions sometimes do better with independent footings to avoid the differential movement problem entirely.
Most garage additions sit on a thickened slab with a stem wall, or a continuous footing with a separate slab pour inside. Either way, the slab edge ties into the foundation system, and the excavation has to leave room for the form work, drain pipe, and vapor barrier. We dig the perimeter to accommodate the wall thickness plus working room on each side.
More on the broader workflow lives on our footings excavation pillar, and adjacent topics include building pads and concrete forming and pouring.
You can pull the original building permit and plans from your jurisdiction, or we can dig a small inspection pit beside the existing foundation to expose and measure the footing bottom. The second option is the most reliable.
That is an engineering decision. Some additions use doweled tie-ins for a rigid connection, others use independent footings with a control joint for intentional separation. Soil conditions, addition size, and load transfer determine the right choice.
Mismatched depth between the new and existing footings, which leads to differential settlement and a cracked seam at the tie-in. Matching depth and bearing soil is the single most important step.
Yes, with care. We avoid undermining the existing foundation and limit how much soil is removed from along the existing wall at any one time. Engineered shoring may be required if the new excavation extends below the existing footing bottom.
