Raleigh Residential Lot Coverage and Impervious Surface Limits
In the City of Raleigh, the maximum portion of a lot that may be covered by structures and other hard surfaces is primarily governed by the zoning district's impervious surface limits. These limits range from 20% in the Residential-1 (R-1) District to 65% in the Residential-10 (R-10) District, representing the total "built-upon area" allowed on a single parcel [Section 9.2.2.A.4.a]. Additional restrictions or allowances may apply if the property is located within a Watershed Protection Overlay District or contains specific environmental features [Section 9.5.1].
Standard Maximum Impervious Surface Coverage
The City of Raleigh Unified Development Ordinance defines the maximum percentage of a residential lot that can be covered by impervious surfaces (built-upon area) based on its base zoning district.
| Zoning District | Maximum Percentage of Impervious Surface Coverage |
|---|---|
| Residential-1 (R-1) | 20% |
| Residential-2 (R-2) | 25% |
| Residential-4 (R-4) | 38% |
| Residential-6 (R-6) | 51% |
| Residential-10 (R-10) and all other base zoning districts | 65% |
Note: For properties that are part of a cluster unit development, townhouse development, or planned development approved prior to May 1, 2001, the City of Raleigh calculates the imputed acreage by combining the individual lot area with the pro rata lot portion of 85% of the common open space [Section 9.2.2.A.4.a].
Defining Built-Upon Area and Building Coverage
To determine the allowed lot coverage in the City of Raleigh, it is important to distinguish between "Building Coverage" and "Built-upon area" (Impervious Surface).
Building Coverage
Building Coverage specifically refers to the maximum area of a City of Raleigh lot permitted to be covered by roofed buildings or structures. This calculation does not include paved areas such as parking lots, driveways, or pedestrian walkways [Section 12.2].
Built-Upon Area (Impervious Surface)
Built-upon area is a broader term used by the City of Raleigh to regulate the total footprint of development. It includes any material that significantly reduces and prevents natural infiltration of water into the soil. Examples include:
- Roofs, chimneys, and eaves.
- Patios, balconies, and stoops.
- Decks (slatted wood decks over unpaved surfaces are considered 50% impervious; if over washed gravel, they are 30% impervious).
- Streets, parking areas, and driveways (including asphalt, concrete, and compacted gravel).
- Concrete, stone, and brick surfaces [Section 9.2.2.F.1, Section 12.2].
Watershed Protection Overlay District Limits
If a residential lot in the City of Raleigh is located within a Watershed Protection Overlay District, the maximum coverage limits are adjusted based on the presence of Stormwater Control Measures (SCMs).
Urban Watershed Protection Overlay District (-UWPOD)
In the City of Raleigh -UWPOD, the following limits apply to new impervious surfaces [Section 9.5.1.B.1]:
| Area Type | No Stormwater Control Measures | With Retention, Detention, or Capture (First 1/2" Runoff) |
|---|---|---|
| Primary WSPA | 24% (or 2 units per acre) | 50% |
| Secondary WSPA | 24% (or 2 units per acre) | 70% |
Falls and Swift Creek Watersheds (-FWPOD & -SWPOD)
For these City of Raleigh overlays, secondary watershed protection areas connected to City water and sewer utilities are generally limited to 12% impervious surface without SCMs. If the site uses SCMs to capture the first 1/2 inch of runoff, coverage may increase up to 24% [Section 9.5.2.B.1, Section 9.5.3.B.1].
Exemptions and Adjustments
The City of Raleigh provides specific exceptions for existing residential structures:
- One-Time 400 Sq. Ft. Exemption: A lot with an existing detached house (Single-unit Living) or an existing attached house (Two-unit Living) is entitled to a one-time 400 square foot increase of impervious surface area without providing additional stormwater control measures, provided the structure existed prior to the application of the ordinance [Section 9.2.2.A.4.a].
- Permitted Overages: The City of Raleigh may allow the standard impervious surface limitations to be exceeded if the applicant demonstrates that the post-development volume of stormwater leaving the site is equal to or less than the volume allowed for that district during a 90th percentile storm [Section 9.2.2.A.4.b].
Sections Cited
- Section 9.2.2.A.4 (Impervious Surfaces Limitations and Other Regulations)
- Section 9.2.2.F.1 (Definitions: Built-upon area)
- Section 9.5.1.B.1 (Urban Watershed Protection Overlay District: Impervious Surface Coverage)
- Section 9.5.2.B.1 (Falls Watershed Protection Overlay District: Impervious Surface Coverage)
- Section 9.5.3.B.1 (Swift Creek Watershed Protection Overlay District: Impervious Surface Coverage)
- Section 12.2 (Defined Terms: Building Coverage, Built-upon area, Lot Coverage)