A garage is not a large shed
The model building code treats a small detached accessory building differently from a garage you can park in. Under the 2021 IRC, section R105.2, a one-story detached accessory structure is often exempt from a building permit when the floor area does not exceed 200 square feet. A one-car garage is usually larger than that, so a permit is the normal case. Zoning still applies either way: setbacks, height, and where on the lot an accessory building is allowed.
Read the accessory-structure section of your zoning code, not only the shed handout. Garages pick up extra rules:
- Location. Many districts keep detached garages out of the front yard and cap how much of the rear yard they can cover.
- Height. Often one story, or a lower cap than the house. A garage with a room above may be regulated as something else entirely — ask before you draw a second floor.
- Separation. If the garage is close to the house or a lot line, the wall facing that side may need a fire rating. The site plan's job is to show the distance; the department tells you whether the wall must be rated.
- A new curb cut across a public sidewalk or curb is often a separate public-works permit, not part of the building permit.
What goes on the garage site plan
County and city garage checklists ask for a scaled plot plan with these items. Foundation, framing, and elevations are additional sheets.
| Element | What to include |
|---|---|
| Lot | Property lines with dimensions, street name, north arrow, scale, address |
| Existing buildings | House and any shed or driveway already there, labeled existing |
| Proposed garage | Length and width, and the use (garage, not “storage” if a car will park in it) |
| Setback dimensions | Perpendicular distances from the garage to each lot line and to the house |
| Overhangs | Some departments want roof overhangs shown when they project more than about a foot and a half, because the setback is measured to the overhang |
| Driveway | Path from the street or alley to the door, width, and surface (concrete, asphalt, gravel) |
| Easements and utilities | Utility or drainage easements, and a well or septic system if you have one |
| Coverage math | Lot area, existing building area, garage area, and the resulting percentage |
Driveway and drainage
Draw the driveway as its own shape and label the material. A gravel drive and a concrete drive are not the same for impervious-coverage rules. In ZoneMapper, set Surface in Layers to Impervious, Permeable, Gravel (uncounted), or Not counted to match how your code treats that surface.
Show an arrow for surface water draining away from the garage. The building code expects the ground to slope away from a foundation; your department will tell you the slope they check. Do not aim that water at a neighbor or into a street inlet you do not own.
How to draw it free in ZoneMapper (about 50 minutes)
1. Start from the survey or the address
Upload the survey if you have one. Otherwise enter the address to load aerial imagery, with a parcel outline where public GIS coverage exists. GIS lines are approximate — check them against a survey before you place a foundation.
2. Trace the lot and the house
Use Lot boundary if the outline is not already there, then Finish lot boundary. Draw the house with Rectangle or Polygon and mark it Existing in Layers.
3. Place the garage
Draw the garage with Rectangle at its real size and leave it Proposed. Enter the accessory-structure setbacks in the Setbacks panel. If the shaded zone covers the garage, move it before you file. Add a text note for the height.
4. Draw the driveway and the dimensions
Use Polygon for the driveway from the street or alley to the garage door. Dimension the garage to the lot lines and to the house with the Dimension tool. If the roof overhang is what the setback is measured to, dimension that edge and say so in a label.
5. Read the coverage and export
Lot coverage updates from the outlines you marked. Compare it with the maximum in your zoning district, fill in the title block, and export the PDF. Keep the structural sheets — slab or footing plan, elevations, and wall bracing — as the rest of the application. Some counties require those sheets to be sealed by an engineer.
Common reasons garage plans are rejected
- Garage placed in the front setback or over a utility easement
- No dimension to the side or rear lot line, or the dimension stops at the wall when the code measures to the eave
- Driveway missing, or a new curb cut with no right-of-way permit
- Lot coverage exceeded once the garage is added to the house
- A second-story bonus room drawn on a permit that only allows a one-story accessory building
FAQ
Can I convert a shed permit into a garage later?
Not by parking a car in it. A garage has vehicle access, a different use, and usually a different size. Apply for the use you are actually building.
Do I need a survey?
Many departments accept a site plan drawn from an existing survey or, for a first look, county GIS lines. If the garage is close to a setback, expect them to ask for a survey. An as-built survey after the pour is a common condition when the building sits near the minimum distance.
Does the driveway count as lot coverage?
Building coverage and impervious coverage are often separate caps. The garage roof usually counts as building coverage. The driveway may count only toward impervious area. Tag the surfaces separately so the two totals stay distinct.
More permit guides
- Shed site plan
- ADU site plan — a unit over or instead of a garage is a different permit
- Home addition site plan
- All permit guides
ZoneMapper is a drafting aid. Accessory-structure size, height, setbacks, fire separation, and driveway permits vary by jurisdiction. Verify them with your building and public-works departments before you submit or build.