Built Upon Area (Impervious) Limits for New Construction

 This page is for impervious limits on residential lots at construction.  For homeowner's lot-level impervious limits, see this page.  For non-lot-level impervious limits, see this page.

 

The following policies have been established by the Johnston County Stormwater Manager to address built upon area (BUA) or impervious surface overages on single-family residential lots.

Questions regarding these policies should be directed to the Stormwater Technician at 919-989-5605 or adam.miller@johnstonnc.gov.

BUA Policies for Existing Development

BUA Not on the Recorded Plat

If the BUA limit or maximum impervious area is NOT on the recorded plat, then the County will not require homebuilders/new home construction to comply with a limit when they apply for building permit. It is up to the builder/owner to verify any restrictive covenants or HOA requirements.

BUA Is on the Recorded Plat

If the BUA limit or maximum impervious area IS recorded on the plat and a building permit is required, then homebuilders/new home construction must comply with that limit when applying for a building permit.

If the homebuilder or new construction will exceed the BUA or impervious area limit

Option 1 - Borrow built upon area from another lot

Homebuilder must document where BUA is coming from and record the BUA limit for the borrowed lot and current lot on a new plat. It is the homebuilder's responsibility to coordinate with developer/engineer, not the County's responsibility.

Option 2 - Borrow from BUA bank in the development

Homebuilder coordinates with developer/engineer to use some of the "banked" BUA. The homebuilder is required to show proof of BUA availability and the final BUA on the lot and in the BUA bank after obtaining the BUA. A new plat shall be recorded with the updated BUA limit.

Option 3 - Roof drain infiltration system 

If a homebuilder wants to install a roof drain infiltration system, the system must be designed by an engineer, and all setbacks must be followed. Record a new plat with new BUA and infiltration device shown in stormwater drainage easement. Contact Environmental Health for septic and well setbacks.

Option 4 - Stormwater control measure (SCM)

If the homebuilder wants to install a different SCM contained in the NCDEQ Stormwater Manual Minimum Design Criteria, the SCM must be designed by an engineer and all setbacks must be followed. Record a new plat with new BUA and stormwater measure shown in stormwater drainage easement. Contact Environmental Health for septic and well setbacks.  Please note that all forms of permeable pavement are not allowed by the county.

Option 5 - Redesign Subdivision

If a large number of lots are involved, the entire subdivision could be redesigned with a regional stormwater facility. An engineered plan revision would need to be submitted and approved.

 

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