Why Georgia Homes Have High Humidity and Hot Floors in Summer (What Spray Foam Addresses)

It is July in Savannah. You walk across the kitchen floor at 7 a.m. and the hardwood feels warm — not from sunlight, but from whatever is going on underneath the house. By noon the air inside feels thick despite the thermostat reading 74. The AC runs almost constantly, your Georgia Power bill climbs past $300, and the crawl space vent covers on the foundation look exactly like they did when the house was built in 1987.

This is not a broken HVAC system. It is a building science problem specific to Georgia’s climate, and it plays out the same way every summer from the Ardsley Park bungalows in Savannah to the Victorian neighborhoods around College Hill in Macon to the brick ranches along Walton Way in Augusta.

georgia’s climate zones make this problem worse than you think

Georgia sits in IECC climate zones 2 and 3 — hot-humid subtropical territory. The practical difference between Savannah (Zone 2, coastal) and Macon or Augusta (Zone 3, inland) is how that humidity arrives and how long it stays.

In Savannah, marine air off the Atlantic and the Savannah River estuary keeps outdoor relative humidity above 80 percent on most summer mornings. The ground under a vented crawl space in a Ardsley Park or Thomas Square neighborhood stays perpetually damp. Moisture does not spike and recede — it is simply always there, pushing upward through the floor assembly.

Macon and Augusta run hotter at peak hours but the humidity pattern is different. Afternoon temperatures regularly hit the mid-90s, and when thunderstorm cells move through from the Gulf and stall over central or eastern Georgia, outdoor humidity jumps fast and stays elevated for days. Crawl spaces in Ingleside Village in Macon or Summerville in Augusta swing between dry-ish mornings and saturated afternoons in a cycle that causes wood to expand and contract, joist hangers to rust, and insulation batts to sag.

In both cases, the underlying physics is the same: warm, humid outdoor air enters a vented crawl space, contacts cooler surfaces (floor sheathing, HVAC ducts, supply plenums), and deposits moisture right where you do not want it.

what a vented crawl space actually does in summer

The original logic behind vented crawl spaces — put vents in the foundation walls to let outside air flush out moisture — works in cold, dry climates. In Georgia it does the opposite.

During summer in any of these three markets, outside air holds more moisture than the air inside a conditioned home. When that warm, wet air enters through the foundation vents, it hits the cooler underside of your floor assembly and the exterior of your HVAC ducts. The dew point is crossed, moisture condenses, and the wood and insulation in your crawl space begin absorbing water they are not designed to hold.

The visible results: floors that feel soft or springy, musty odors migrating up through gaps around plumbing penetrations, and HVAC equipment working harder because it is trying to dehumidify air that is being continuously refreshed with outdoor humidity through every vent opening in the foundation.

The Georgia Energy Code has recognized this for years. Sealed and conditioned crawl spaces are now a standard path to compliance precisely because vented crawl spaces in Zones 2 and 3 create chronic moisture problems rather than solving them.

where spray foam changes the equation

Closed-cell spray polyurethane foam applied to the crawl space walls and rim joists converts a vented crawl space into a semi-conditioned enclosure. The mechanism is straightforward.

By air-sealing the rim joist — the band of framing that sits on top of the foundation wall and is responsible for a significant fraction of a home’s total air leakage — spray foam stops the highway between outdoor air and the floor assembly. Warm, humid outdoor air no longer has a direct path to the cold supply-duct surfaces or the underside of the subfloor.

Closed-cell foam also adds an R-value per inch (roughly R-6 to R-7 per inch) and, critically, functions as a vapor retarder. A two-inch application on a crawl space wall provides both the thermal resistance and the moisture control in a single material. Fiberglass batts stapled between floor joists provide neither — they trap moisture, compress over time in humid conditions, and fall out of place, leaving gaps that undo whatever R-value they once had.

For homes in Macon and Augusta where duct systems run through unconditioned crawl spaces, spray foam on the crawl space walls brings the duct system inside the thermal envelope. That means supply air is no longer being warmed by the crawl space before it reaches your registers, your equipment runs fewer cycles to meet setpoint, and your Georgia Power bill reflects it.

what homeowners in these markets notice first

The most immediate change after a crawl space is sealed and conditioned with spray foam is humidity inside the living space. Homeowners in older Savannah neighborhoods — Midtown, Gordonston, the streets east of Forsyth Park — frequently report that their indoor relative humidity drops from the mid-60s to the low-to-mid 40s within a few weeks of the work being completed, without any change to the HVAC equipment.

In Macon and Augusta, the feedback is often about floors specifically. The warm, slightly soft floor feel disappears. That sensation is a direct result of floor sheathing that has absorbed moisture from below — once the crawl space is sealed and that moisture source is removed, the floor system dries out and stabilizes.

Energy savings follow, though they take a full billing cycle or two to become visible on a Georgia Power statement. The combination of reduced duct loss, lower infiltration, and less latent load on the air handler typically produces meaningful reductions in summer cooling costs for homes where the crawl space was previously vented and uninsulated.

If your Georgia home runs high humidity indoors in summer, the floor assembly and crawl space are the right place to start the investigation — not the thermostat setting.

Contact a spray foam contractor serving the Savannah, Macon, or Augusta area to have your crawl space evaluated before the peak of summer cooling season arrives.