York County, SC Crawl Space Guide: Code, CL-100 & Clay Soils

Updated October 2026. General information, not legal or engineering advice. Confirm current requirements with the agency listed before work begins.

Key facts

Topic	Summary	Source
Residential code	2021 IRC with South Carolina modifications; effective for local jurisdictions January 1, 2023	SC Building Codes Council
Builder license	Residential builder license required for jobs over $5,000	S.C. Code Title 40, Ch. 59
Specialty trades	Licensure or registration for residential specialty work over $500	S.C. Code Title 40, Ch. 59
CL-100 moisture	20%+ wood moisture or standing water is excessive moisture; decay fungi active at 28%+	S.C. Code Regs. 27-1085
Rock Hill permits	Online portal; city business license required for contractors and subcontractors	City of Rock Hill
County permits	York County Building and Codes; checks state contractor licensing	York County
Precipitation	About 42.6 inches a year in Rock Hill	Wikipedia (NOAA data)

What is York County's ground like?

The USDA Soil Conservation Service's Soil Survey of York County, South Carolina, issued in 1965, maps a wide range of Piedmont soils. Cecil soils developed in residuum weathered from granite and gneiss, and Appling soils are deep, well-drained upland soils. Iredell soils developed from basic rocks and have a yellowish-brown plastic clay subsoil. The survey's Iredell-Mecklenburg-Davidson association, about 60 percent Iredell soils, covers parts of the southeastern and northeastern county. Tatum soils, formed from sericitic schist, dominate an association in the northwestern part of the county, where Kings Mountain National Military Park sits, and another area in the southeast. For a crawl space, the takeaway is that most of the county has clay subsoils that don't absorb heavy rain quickly, so drainage around the house matters.

Why crawl spaces here get damp

Rock Hill's climate is humid subtropical, with hot, humid summers, cool winters and about 42.6 inches of precipitation a year. The U.S. Department of Energy's Building America program explains that in humid climates the outside air is often moister than the crawl space air, so traditional vents can feed moisture, mold and pest problems. Its research on sealed, conditioned crawl spaces found humidity reductions of more than 20 percent and heating and cooling savings of 15 to 18 percent.

What does the code require?

The SC Building Codes Council adopted the 2021 International Residential Code with South Carolina modifications, effective for local jurisdictions on January 1, 2023. A vented crawl space generally needs 1 square foot of vent per 150 square feet of floor area, or 1 per 1,500 square feet with an approved ground vapor retarder, with a vent within 3 feet of each corner. An unvented crawl space needs a continuous vapor retarder over exposed earth, joints overlapped 6 inches and sealed or taped, edges extended at least 6 inches up the stem wall and sealed, and one approved air option: continuous exhaust at 1 cfm per 50 square feet, conditioned air supply at the same rate, a plenum, or dehumidification at 70 pints a day per 1,000 square feet. Access openings must be at least 18 by 24 inches through a floor and 16 by 24 inches through a wall.

Licensing rules

Residential builders. Title 40, Chapter 59 of the S.C. Code requires a Residential Builders Commission license when the cost of the work exceeds $5,000.
Residential specialty contractors. The same chapter requires licensure or registration for specialty work over $500, including trades such as carpentry, masonry and insulation.
Rock Hill business license. The city requires a business license for all design professionals, contractors and subcontractors before a permit is issued.
York County. The county's Building and Codes division checks that contractors hold South Carolina licenses. It doesn't require a business license for work in unincorporated areas.

The CL-100 and crawl space moisture

S.C. Code of Regulations 27-1085 governs the Official South Carolina Wood Infestation Report, the CL-100, which many lenders and buyers ask for. The inspection covers accessible crawl spaces and must include representative wood moisture readings around the interior perimeter. The regulation defines excessive moisture as readings of 20% or more, or standing water in the crawl space or around the foundation, and notes decay fungi become active at 28% and above. Corrections it mentions include a polyethylene vapor barrier over the soil, added ventilation, or a sump and drain system for poor drainage.

Permits around the county

The City of Rock Hill accepts residential permit applications online, for new homes and for additions, renovations and repairs. Staff typically return plan review comments in about three business days, and fees are invoiced by email and paid through the portal. York County's Building and Codes division handles permits and inspections in unincorporated areas. Fort Mill, Tega Cay, York and Clover are separate municipalities, so check with the office for your address.

What affects the cost of crawl space work?

Every job is priced after an inspection, and typical totals vary widely. Common factors:

Crawl space area, height and access
Drainage or sump work needed first
Liner thickness and coverage of walls and piers
Removing old plastic, insulation and debris
Air control method and electrical work
Wood repairs, permits and any historic review

Questions to ask a crawl space contractor

Which South Carolina license or registration do you hold for this job?
Do you have a Rock Hill business license, if I'm in the city?
What's causing the moisture, and what will you fix first?
Which code air option are you proposing for a sealed crawl space?
Will this address the CL-100 finding?
What's warrantied in writing, and what upkeep is expected?

Common questions

Which building code applies in York County?

The 2021 International Residential Code with South Carolina modifications, effective for local jurisdictions since January 1, 2023.

When is a South Carolina residential builder license required?

When the cost of the work exceeds $5,000. Residential specialty contractors need licensure or registration for work over $500.

What soils are common in York County?

The county soil survey maps Piedmont soils including Cecil, Appling, Enon, Iredell and Tatum, many with clay subsoils.

York County crawl space guide (2026)