Generator Permits and Placement: What Inspectors Check

Which permits a standby generator needs, what they cost, how far from windows and the house it must sit, and what the inspector actually checks.

A permanently installed standby generator is an engine burning gas next to your house, hard-wired into your electrical service. Every jurisdiction wants to look at that before it runs. The permit is not the obstacle people expect — your installer handles it — but knowing what’s involved is how you tell a good installer from a cheap one.

Which permits

Fees are set by the municipality and typically total $200–$500 across the permits. The installer passes them through at cost; a quote that says “permits by owner” is one to walk away from.

Skipping permits isn’t a shortcut. An unpermitted generator can void a homeowner’s insurance claim after a fire, surfaces during a home sale, and — because the transfer switch is the thing that keeps generator power off the utility’s lines — puts line workers at risk if it’s wrong.

Where the unit can go

Placement is governed by NFPA 37 (the standard for stationary engines), the manufacturer’s installation manual, and local code, which can be stricter than either. The manual is usually the binding document; inspectors check against it.

The rules address four things:

1. Distance from the house. Air-cooled units with the manufacturer’s listed enclosure are often permitted closer to the wall than the generic standard — commonly around 18 inches — but only on non-combustible walls and only with that specific listing. Otherwise the distance grows.
2. Distance from openings. Windows, doors, vents, soffit vents — typically several feet, measured from the exhaust. Exhaust contains carbon monoxide; this is the rule that matters most.
3. Distance from combustibles. Fences, decks, stored fuel, vegetation.
4. Service clearance. Room around the unit to open panels and change the oil — commonly three feet on the service side.

Plus the practical ones: a level pad above grade (in flood zones, above the base flood elevation), away from where snow slides off the roof, and where the noise — roughly a lawnmower at a distance — won’t land under a bedroom window or on a neighbour.

An installer who walks you to a spot and explains the distances has done this before. One who says “we’ll find a place” is going to find it on install day, and it may be the wrong one.

What the inspector looks at

Electrical inspection

• Transfer switch listed for the purpose, correctly rated, and wired so generator and utility can never feed each other
• Grounding and bonding of the generator and the switch
• Conductor sizing, conduit, and the disconnect
• Labelling at the service equipment: there is now a second power source

Gas inspection

• Pipe sizing for the generator’s demand (a 20 kW unit can draw 200–300 cubic feet per hour at load) — undersized pipe is a common failure
• Pressure test of the new run
• Shutoff valve within reach, sediment trap, correct regulator
• For propane: tank placement distances and line depth

Final

• The unit runs, transfers on a simulated outage, and transfers back
• Clearances as built match the manual

Failures are almost always one of: pipe sized too small, generator too close to a window, or a transfer switch that isn’t actually a transfer switch. All three are the installer’s job to get right and to fix.

Timeline

Permit issue takes days to a couple of weeks depending on the municipality; the utility meter upgrade, if you need one, can take longer than the whole rest of the project. Install itself is typically one to two days. Inspection is scheduled after. Demand spikes after major storms and the whole timeline stretches — shoulder seasons are faster and often cheaper.

Before you sign, ask: which permits, who pulls them, what’s the fee, and where exactly does the unit sit? The other eleven questions worth asking →