Charging a Car Parked in an Alley-Access Detached Garage
The central Austin problem: the panel is in the house, the car is behind it, and a protected tree sits between them. How these installs get routed.
By Austin EV Charger Installers
There is a specific installation that central Austin produces more than anywhere else on this site, and it has three constraints stacked on top of each other.
The panel is on the house. The car parks in a detached garage off the alley. And somewhere between them is a mature tree that the city protects.
Why this is so common here
The pre-war and mid-century neighbourhoods — Hyde Park, Rosedale, Travis Heights, Bouldin, much of east Austin — were platted with alleys and built with detached garages at the back of the lot. A century of tree growth later, those lots have substantial canopy, and the sensible cable path from the house to the garage runs directly beneath it.
None of this is a problem. It is a design question that needs answering before anyone quotes, rather than discovered halfway through a trench.
The tree rules, concretely
A tree with a trunk diameter of 19 inches or more, measured at four and a half feet above the ground, is a protected heritage tree. Trees under that are not regulated on residential property.
The ground a protected tree occupies is its critical root zone, and the rule is straightforward: one foot of radius for every inch of trunk diameter. A 24-inch pecan therefore has a critical root zone reaching 24 feet out in every direction — a circle roughly 48 feet across.
Construction, excavation or trenching that significantly impacts that zone requires review, through a Tree Ordinance Review Application, even when the tree itself is untouched. That last part is what surprises people. You are not proposing to remove anything. The ground is still protected.
On a standard central Austin lot, one mature tree can put most of the back garden inside a protected zone.
What that changes in practice
Four routes are worth considering, and the tree is often what decides between them:
Around the zone. Longer, but ordinary trenching. Frequently the answer, and the reason a quote here may propose a path that looks indirect on a plan.
Overhead. Avoids the ground entirely. Has its own clearance and appearance considerations, and interacts with whatever else already runs along the alley, but on a lot where the root zone genuinely blocks the direct path it is a legitimate answer rather than a fallback.
Through existing structure. Along a fence line, under a deck, through a breezeway. Depends entirely on what is there.
Move the charger. If the constraint is severe enough, mounting on the house and parking the car a few feet differently can remove the problem altogether. Not always acceptable, always worth raising.
The point is that an installer who has not looked at the trees has not finished quoting your job.
The other half: distance and voltage drop
Detached garage runs are long by the standards of a modern suburban installation. Sixty, eighty, sometimes over a hundred feet.
Voltage drops over distance. A circuit sized against the breaker rating alone can arrive at the garage measurably weaker than it left, and the result is charging that consistently underperforms with nothing obviously broken to point at.
Conductors get sized against the measured run, not the breaker. On a long garage run that means heavier cable than the table suggests, and it is the difference between a circuit that works properly for twenty years and one that quietly disappoints.
When a subpanel is the better answer
If the garage already has anything electrical — lighting, outlets, a workshop, a freezer — then running a subpanel out there rather than a single long branch circuit is frequently better design.
A sub-panel costs a little more up front. It gives you distribution at the garage rather than one dedicated circuit, which means the next thing you want out there is a breaker rather than another trench across the same protected root zone.
On these lots, where opening the ground is the expensive and constrained part, doing it once and doing it properly is worth the difference.
And the panel itself
Worth remembering that these are also the houses most likely to have a 100-amp service, or occasionally less. The load calculation matters here as much as the routing does, and on a Hyde Park bungalow both questions are live at the same time.
Which is the honest reason these installations take a proper site visit rather than a phone call.