How to Draw a Site Plan for an Outdoor Equipment Permit

Why this matters

A standby generator, a condenser, a pool heater or a heat pump on a new pad usually needs a permit, and the permit usually needs a site plan: the lot, the house, and exactly where the new equipment sits. Two different rules decide where that is. The manufacturer's installation manual sets clearances the listing depends on, mostly about exhaust, airflow and service access. The local zoning or building rule sets how close equipment may sit to a property line. A spot that satisfies one and not the other gets the permit held, or worse, gets built and then cited, and moving a set pad with a gas line and a conduit run already trenched in is a second job. The plan's job is to show the reviewer, and the crew, that one spot satisfies both.

The two rule sets, and why both go on the sheet

The manufacturer's clearances are part of the product's listing. The installation manual gives them as a table or a figure: minimum distance from the unit to the building wall, to windows, doors, soffit vents and other openings, to other equipment, and the clear space needed in front of service panels. For a generator, the opening distances exist because engine exhaust carries carbon monoxide. NFPA 37, the standard for stationary combustion engines in the edition your jurisdiction has adopted, sets a default separation between an outdoor engine and the building's walls and openings, and many manufacturers' listings permit closer spacing for an enclosure tested to it. Use the number in this unit's manual, because it is the number the inspector will hold you to.

The local rule lives in the zoning code or the building department's equipment rules. It may set a side-yard setback for mechanical equipment, forbid equipment in a front yard, add a noise limit at the property line, or exempt small units entirely. It differs town by town, and sometimes a homeowners' association adds its own. Call or read the code; do not reuse the last town's answer.

The utility's rules are a third, smaller set: clearance around the gas meter and regulator vent, and access to the electric meter. The utility publishes them, often in a service handbook.

A plan that shows only the manual's clearances invites the reviewer to check the setback themselves, and a plan that shows only the setback invites the inspector to find the window. Dimension both, so the reviewer can check each in a few seconds.

The steps

1. Get the plat or survey before you measure anything. The recorded plat or the survey from the home's purchase shows the lot lines and lot dimensions. Why: the property line is a legal line, not a physical one, and a fence, a hedge or the edge of the lawn is commonly off it by a foot or more. What breaks if skipped: you dimension the setback to the fence, the fence is 2 ft inside the line, or 2 ft outside it, and your setback is wrong by that much in an unknown direction. If there is no survey and no visible property pins, label the line "per plat, not field verified" and ask the department whether that is acceptable; some will require a survey for a tight side yard.

2. Pull the three rule sets for this unit and this lot. The installation manual's clearance figure for the exact unit, the local setback and placement rule for mechanical equipment, and the utility's meter clearances. Write each as a one-line rule on a scratch sheet with its source. What breaks if skipped: you place the pad by habit and discover the governing number at review.

3. Measure the house from two fixed corners. Tape the house's overall dimensions, then measure from the nearest house corner to the property line along two perpendicular directions, cross-checked against the plat. Why: the house is the only thing on site you can measure to with confidence, so everything else hangs off it.

4. Walk the wall the equipment goes beside and locate every opening by chainage. Chainage means distance along the wall from one named corner: window from 12'-0" to 15'-0", dryer vent at 17'-6", gas meter at 20'-0". Include operable windows, doors, soffit and foundation vents, the dryer and bath exhaust terminations, the electric meter and any existing equipment. What breaks if skipped: the opening you did not record is the one 4 ft from the exhaust.

5. Draw at an engineering scale on one sheet. A residential lot commonly fits on letter or tabloid at 1 inch = 10 feet or 1 inch = 20 feet. Draw the lot lines, the house footprint, the driveway, and the wall you walked, with every opening marked. See related: Architectural and Engineering Scales on One Ruler. Why engineering scale: site plans are read in feet and tenths with an engineer's scale, and a reviewer expects it.

6. Place the pad and dimension every rule that touches it. Show the pad's size, then a dimension from the pad to the house wall, to each property line in reach, to the nearest opening, and to each meter, and the service clearance in front of the unit drawn as a dashed box. Why: each rule gets one dimension line the reviewer can read without a scale.

7. Show the routes and the notes. The gas line route from the meter, the electrical route to the transfer switch or disconnect, the trench, and a note that the trench will be located through 811, the national call-before-you-dig number, with the notice period your state's law sets. Note who does the gas piping and the electrical work. Both are licensed work where your state or locality licenses them; if your shop does not hold those licenses, the plan names the subcontractor who does.

8. Add a title block, a north arrow and the source of every number. Address, owner, preparer, date, scale, the unit's model designation as it appears on the permit, and a short note citing the manual page and the code section for each clearance. What breaks if skipped: the reviewer cannot tell your 5 ft from a guess.

Worked example: a generator on a tight side yard

The lot is 60 ft wide by 120 ft deep, front to the south. The house is 40 ft wide and 32 ft deep, set 25 ft back from the front line, 11 ft from the west line and 9 ft from the east line (11 + 40 + 9 = 60, which closes). The homeowner wants the generator on the east side, near the gas meter. Values are this site's; the clearances below are taken from this example unit's manual and this town's code, and yours will differ.

• Manual: back of unit at least 18 in from the house wall; at least 5 ft from any window, door or opening; 3 ft clear in front of the service side.
• Town: mechanical equipment in a side yard at least 5 ft from the side property line.
• Utility: keep the unit outside a stated radius around the gas regulator vent.

East wall chainage from the front (south) corner: bedroom window 12'-0" to 15'-0", dryer vent 17'-6", gas meter and regulator 20'-0".

First placement. The tech sketched a 3 ft by 5 ft pad, long side along the wall, back edge 18 in off the house, from chainage 14'-0" to 19'-0". Check each rule from those numbers:

• Wall: 1.5 ft, passes.
• Property line: the pad's outer edge is 1.5 + 3 = 4.5 ft from the house, so 9 - 4.5 = 4.5 ft from the east line. The town wants 5 ft. Fails by 0.5 ft.
• Window: the window ends at 15'-0" and the pad starts at 14'-0", so the pad overlaps the window's run. Fails.
• Dryer vent: 17'-6" sits within the pad's run. Fails.

Moving the pad along the wall cannot fix the setback, because the side yard is only 9 ft and the pad plus its wall clearance takes 4.5 ft of it. Rotating it makes it worse: long side out, the outer edge lands 1.5 + 5 = 6.5 ft from the house and 2.5 ft from the line. This side yard cannot take this unit under this town's rule, whatever the manual allows.

Second placement, rear wall. The rear yard is 120 - 25 - 32 = 63 ft deep. The rear wall has a patio door from 18'-0" to 24'-0" measured west from the rear east corner, and a hose bib at 10'-0", which is not an opening and stays reachable beside the pad. The pad goes along the rear wall, back edge 18 in off it, from 2'-0" to 7'-0" west of the corner.

 N ^     REAR PROPERTY LINE
 +--------------------------------------------+
 |              REAR YARD 63'-0"              |
 |                                            |
 |                          PAD 3x5, 1'-6"    |
 |       PATIO DOOR         off rear wall     |
 |       18' to 24' W   [=====]  11'-0" to E  |
 | 11'-0" +------------------------+ line     |
 |<------>|  HOUSE 40'-0" W        |          |
 | W LINE |        x 32'-0" D      |[M] GAS   |
 |        |                        |  20'-0"  |
 |        |                     WIN|  12'-15' |
 |        +------------------------+<-9'-0"-->|
 |             FRONT SETBACK 25'-0"           |
 +--------------------------------------------+
            FRONT PROPERTY LINE, STREET
 LOT 60'-0" x 120'-0"   NOT TO SCALE
 E wall chainage from front corner; rear wall
 chainage measured west from rear east corner

Checks:

• Wall: 1.5 ft, passes.
• East line: the house's east wall is 9 ft from the line and the pad starts 2 ft inside that wall's line, so 9 + 2 = 11 ft. Passes the 5 ft rule with 6 ft to spare.
• Patio door: the pad ends at 7'-0" and the door starts at 18'-0", 11 ft apart. Passes 5 ft.
• Rear line: 63 ft of yard less the 1.5 ft and the 3 ft pad leaves 58.5 ft, nowhere near a setback.
• Gas meter: still at chainage 20'-0" on the east wall, 32 - 20 = 12 ft from the rear corner, so the gas line runs about 12 ft along the east wall plus about 4 ft to the pad. That route goes on the plan, along with the note that the gas fitter sizes the line for the unit's full input over its actual length.

What the choice cost. The east-side spot looked shorter on gas pipe, but it failed three of its four checks. The rear spot adds pipe and conduit length, which the gas fitter and the electrician price, and it passes every rule with margin. A reviewer reading the second plan sees four dimension lines and four passes.

Where the answer flips

The town exempts small equipment from setbacks, or measures from the pad to the line differently (to the unit rather than the pad, or allows a reduced setback with a sound-rated enclosure). Then the east side might pass on setback, and the window and dryer vent become the only constraints. Read the code text, and if it is ambiguous, ask the department in writing.

A condenser instead of a generator. The opening distances usually shrink or disappear, because there is no exhaust; the manual's clearances are about airflow to the coil and service access, and the local setback and noise rules carry more weight. Recirculation between two condensers, or between a condenser and a wall corner, is a manual clearance too.

A corner lot. Many codes treat both street sides as front yards, which can forbid equipment on a side that looks like a side yard.

Before you submit

Re-add every dimension that should close against the plat: the house plus its two side yards should equal the lot width, and the front setback, house depth and rear yard should equal the lot depth. Confirm every opening within 10 ft of the pad is drawn with its chainage, and that each rule appears once on the sheet as a dimension with its source noted.

References

• See related: Architectural and Engineering Scales on One Ruler
• See related: How to Sketch a Floor Plan for a Permit Application
• See related: Residential Permit Drawings: What a Plan Reviewer Checks
• NFPA 37, Standard for the Installation and Use of Stationary Combustion Engines and Gas Turbines, in the edition your authority having jurisdiction has adopted, read together with the unit's installation manual
• 811 call-before-you-dig notification, as required by your state's damage prevention law