Overlay Districts and Historic Review
Summary
An overlay district adds rules on top of a parcel's base zoning for a special purpose such as historic preservation, flood hazard, airport safety, or design quality, and historic overlays usually require review of exterior changes by a commission. Overlay review can add months and change materials, windows, and massing, so check for overlays before buying, programming, or designing a site.
Cols
Scope
- Overlay boundaries, standards, and review procedures are set by each local ordinance. Always verify the municipal code's definitions and the current zoning and overlays for the project parcel
- Covers the overlay concept, common types, and historic design review with certificates of appropriateness
- Federal and state preservation programs, such as tax credits and National Register listing, are separate from local review and are not covered here
Terminology
- Overlay district: a zoning layer mapped over one or more base districts that adds or changes requirements
- Base district: the underlying zoning that continues to apply unless the overlay replaces it
- Historic overlay (historic district): an overlay protecting the character of historic buildings and areas
- Certificate of appropriateness (COA): the approval of a historic commission for exterior work in a historic overlay
- Design review board: a body that reviews the appearance of new buildings and changes
- Design guidelines: adopted standards for materials, massing, proportions, and details
- Contributing and noncontributing buildings: buildings that do and do not add to the historic character of a district
- Floodplain overlay: an overlay that applies flood hazard rules to mapped areas
- Airport overlay: an overlay limiting height and use near an airport
- Administrative review: staff approval of minor work without a commission hearing
Classification
Common overlay types
| Overlay | Purpose | Typical effect |
|---|---|---|
| Historic | Preserve character | Design review of exterior changes, demolition review |
| Design review | Raise design quality in a corridor or district | Review of materials, massing, facade design |
| Floodplain | Reduce flood damage | Elevation, flood-resistant construction, use limits |
| Airport | Protect flight paths | Height limits, noise and use restrictions |
| Environmental | Protect wetlands, slopes, shorelines | Buffers, grading limits |
| Transit-oriented | Encourage dense development near transit | Higher density, reduced parking |
- An overlay can be more restrictive or, as with transit-oriented overlays, more permissive than the base district
- When an overlay and the base district conflict, the ordinance states which controls; the more restrictive usually does
Requirements
Historic design review
- Trigger: a certificate of appropriateness is typically required before exterior alterations, new construction, additions, and demolition in a historic overlay; interior work usually is not reviewed
- Staff versus commission: minor work such as repairs in kind or paint may be approved administratively by staff; larger projects go to a commission or review board that meets on a regular schedule, often monthly
- Standards: decisions rest on adopted design standards for each district; guidelines typically do not dictate a particular style or specific designs
- Decisions: a board may approve, deny, or approve with conditions; one ordinance requires a decision within 30 days of review
- Appeals: denials may be appealed; the route varies, in some places to the board of zoning appeals and in others only to a court
- Enforcement: work without approval can lead to stop work orders and enforcement
- Sequence: historic approval generally comes before or alongside the building permit
Documents
- Application form, site plan, elevations, and photos of existing conditions
- Material and window samples, product data, and details
- Description of the work and how it meets the guidelines
Worked examples
Window replacement in a historic district
| Step | Action | Result |
|---|---|---|
| Check | Parcel in a historic overlay | COA needed for exterior changes |
| Scope | Replace 12 wood windows with vinyl | Likely not consistent with guidelines that favor original materials |
| Staff discussion | Pre-application meeting | Repair or match wood profiles and muntin patterns |
| Application | Elevations, window sections, samples | Staff or commission decision |
| Timeline | Commission meets monthly; decision within 30 days in one ordinance | Plan 1 to 3 months before building permit |
Addition to a contributing building
| Step | Check | Result |
|---|---|---|
| Placement | Rear or side, set back from the front facade | Preferred by most guidelines |
| Height | Lower than the original building | Keeps the historic form dominant |
| Materials | Compatible but distinguishable | Review for consistency with guidelines |
| Approval path | Commission hearing | Public notice, hearing, conditions |
Floodplain overlay
| Step | Check | Result |
|---|---|---|
| Parcel in a mapped flood area | Floodplain overlay applies | Lowest floor elevation and materials rules apply |
| Effect on design | First floor raised or flood-proofed | Changes height, entry, and stair design |
| Interaction | Height limit measured from the required elevation or natural grade | Confirm the measurement point |
Coordination
- Due diligence: check the zoning map and overlay maps before site purchase
- Owner and consultants: build review time and a historic consultant into the schedule when needed
- Pre-application: early meetings with staff narrow the issues before a hearing
- Product selection: guidelines drive window, siding, roofing, and trim choices; get approval before ordering
- Building code: historic buildings may use alternative compliance paths in the existing building code
- Neighbors and public: hearings bring public comment; prepare drawings that read clearly
Common issues
- Missing overlay: work begun on a base-district permit without a COA
- Material substitutions: a field change of window or siding after approval needs a new review
- Demolition delay: demolition review can add time or prevent demolition
- Contradictory standards: the overlay may lower the base district's height or setbacks
- Interior-only assumption: some districts review visible interior changes at storefronts or public buildings
- Conditions late in the process: commission conditions affect drawings already issued
Standards
- Local historic district ordinance and guidelines: the controlling standards
- Secretary of the Interior's Standards for the Treatment of Historic Properties: common basis of local guidelines
- FEMA flood maps and local floodplain ordinance: basis of floodplain overlays
Sources
- Franklin, TN: certificate of appropriateness, https://www.franklintn.gov/government/departments-k-z/planning-and-sustainability/historic-preservation/certificate-of-appropriateness
- Wikipedia: Zoning in the United States, https://en.wikipedia.org/wiki/Zoning_in_the_United_States