Charging an EV in the attached garage of a sprinklered house

Drive through an Ashburn or Reston cul de sac at night and half the garages have a charger glowing on the wall. The question that comes with it, usually from someone who just bought a sprinklered townhouse or had a retrofit done, is whether the sprinklers cover the car. The short answer is that they usually do not, because the garage is the one room most 13D systems leave out. The longer answer is what an EV fire actually is, what the wall between the garage and the house does, how to get the charger in with a permit, and what it takes to put a head over the car if you want one.

The garage is probably not sprinklered

NFPA 13D does not require heads in an attached garage, and most builders in Fairfax, Loudoun, and Prince William took the exemption to keep the bid down. The rooms without sprinklers article lists the exempt spaces and why the standard draws the line where it does. The system is built to get the people out of the bedrooms, not to save the contents of the garage. Walk out and look at the garage ceiling. A white cover plate or a bare brass head means it is covered. Bare drywall means it is not, and the house side of the system does not reach past the door.

What an EV fire is, and is not

Battery fires in cars are rare, rarer per vehicle than gasoline fires. When one happens it is a different animal. A pack in thermal runaway makes its own heat and oxygen, burns hot for a long time, and relights after it looks out. Water does not put the pack out. What water does, from a hose line or a sprinkler head, is cool everything around the pack so the fire stays a car fire instead of becoming a house fire. The e-bike battery article covers the small pack version; a car is the same chemistry at a hundred times the size or more, sitting against the wall that holds up your kitchen.

So a head over the car is not there to extinguish the car. It is there to keep the garage ceiling, the door into the house, and the framing above from catching while the fire department drives over from the Ashburn or Franconia station.

The wall between the garage and the house

The residential code every Northern Virginia county enforces already puts a fire separation between an attached garage and the living space. Gypsum board on the garage side of the shared wall and the ceiling under any bedroom, and a solid or fire rated door that is not a hollow core interior door. That separation, not the sprinkler system, is the first thing standing between a car fire and the house. Two things undo it on a regular basis. A cat door or a dryer vent cut through the wall, and a door that gets propped open with a brick because the charger cable runs through it. Keep the wall whole and keep the door shut while the car charges.

Getting the charger in

A Level 2 charger is a 240 volt appliance on its own circuit, generally 40 to 60 amps. In Fairfax, Loudoun, Prince William, Arlington, and Alexandria that is an electrical permit, pulled by a licensed electrician, inspected before the cover goes on. Two things come up in this area more than most.

• Older panels. A 1970s Burke or Springfield split level on a 100 amp service may not have the room. The electrician does a load calculation, and the answer is sometimes a panel upgrade or a charger that throttles when the dryer runs. Do that math before buying the unit, not after.
• Where the cable lands. A charger mounted so the cable crosses the door into the house, or drapes over the sprinkler riser if the riser lives in the garage, is a daily nuisance and an inspection comment. Mount it on the wall nearest the car’s charge port and away from the riser and the panel clearance.

Skip the extension cord and the plug in unit on a shared circuit. Most garage fires that start at a charger start at a cord or an outlet that was never meant to run at full load for eight hours, not at the car.

Adding a head over the car

Putting a sprinkler head in the garage is one of the smaller jobs we do. The pipe comes off the nearest branch inside the house, through the shared wall, to one or two heads at the garage ceiling. It is a permit, a one page drawing, and usually a single day. Three details make it work here.

1. The garage is cold. An attached garage in Loudoun drops below the 40 degree line on a normal January night, and a wet pipe in it will freeze. The head is a dry pendent or a dry sidewall, with the water held back on the heated side of the wall, the same approach the freeze protection article describes for porches. A heated garage with a real thermostat can take a wet head.
2. The temperature rating. A head near a gas furnace, a water heater, or a south facing garage door that bakes in July gets an intermediate temperature head so a hot afternoon cannot open it. The head temperature article has the ratings.
3. The water calculation. Adding heads adds demand. On a house with a 1 inch service it rarely matters. On a townhouse on a 3/4 inch line, the water meter article explains why the designer checks the numbers before promising the head.

We quote garage heads per head, the same way the moving heads article describes for a remodel. Ask for the number with the drawing.

What the garage still needs even with a head

Garages get a heat detector, not a smoke alarm, because car exhaust and dust set smoke alarms off. If the house alarms are interconnected, a heat detector on the garage ceiling tied into them is a cheap addition the electrician can do during the charger install. The smoke alarms article covers how the two systems share the job. A monitored flow switch on the sprinkler riser, in the monitoring article, means a head opening at 3 a.m. calls someone even if the car owner is asleep upstairs.

Insurance and the HOA

Carriers ask about EVs on some renewal forms now, and a few ask about the charger install. A permitted install with an inspection sticker is the answer they want. Whether a sprinkler head in the garage moves the premium is carrier by carrier; the insurance discount article explains how to ask. In a townhouse the garage wall is usually a party wall, so the HOA and the neighbor have an interest; the HOA article covers what to send the board before the charger or the head goes in.