# Crawl Space Encapsulation Fixed Our Humidity in Murfreesboro > A Murfreesboro home's AC ran nonstop but humidity hit 72%. Crawl space encapsulation solved it — no new HVAC needed. See what we found and how we fixed it. Murfreesboro Crawl Space Encapsulation Pros | crawl space encapsulation | Murfreesboro, TN ## The Call: "My AC Runs All Day and My House Still Feels Like a Swamp" It was mid-July — the kind of Murfreesboro week where the dew point sits above 70°F before 8 AM and doesn't budge until well after dark. A homeowner in a 1990s-era two-story subdivision off Shelbyville Pike called us frustrated. Their central air conditioning was running almost continuously, the electric bill was climbing, and a thermostat hygrometer in the living room was reading 68–72% relative humidity day after day. An HVAC contractor had already been out. The diagnosis? The system was "undersized." The quote for a larger-tonnage unit was sitting on the kitchen counter. Something about that didn't sit right with the homeowner. The house had never had this problem when they first moved in. They'd heard crawl space moisture could cause indoor air quality issues, and they asked us to take a look before committing to new equipment. Smart call. That phone call saved them thousands of dollars. --- ## What We Found on Site: A Crawl Space Doing the Opposite of Its Job The home has a partial crawl space under its original 1990s footprint — the rear addition is slab-on-grade — so we suited up and went in. What we found was textbook. The ground was covered with a single layer of thin 6-mil poly sheeting, loosely laid and unsealed at the seams and edges. In the crawl space world, that's not a vapor barrier — it's a suggestion. Moisture from the soil was migrating freely around every unsealed edge and seam, and the open foundation vents around the perimeter were doing exactly what open vents do in a Middle Tennessee summer: pulling in hot, saturated outdoor air and cycling it through the underfloor assembly. The subfloor above showed visible surface condensation staining on the joists. The insulation batts between the floor joists — kraft-faced fiberglass — were sagging and had lost most of their effective R-value from repeated wetting. The wood moisture content readings we took at the rim joist and lower joist faces were elevated well above the 19% threshold where biological growth becomes a real concern. Here's the key finding: **the HVAC system was correctly sized for the home's thermal load.** It was keeping the temperature right where the thermostat asked. But it was never designed to handle the latent load — the moisture load — being continuously introduced from below. A bigger air conditioner would have cooled the air faster, but it would have cycled off sooner, running even shorter cycles and doing *less* dehumidification, not more. The homeowner would have spent $8,000–$12,000 on new equipment and still lived in a humid house. The real problem was the crawl space. Full stop. --- ## How We Fixed It: Crawl Space Encapsulation Done Right We laid out the full scope of work before touching anything. No surprises, no scope creep — just a clear plan with a fixed price. **Step one: remove and dispose of the existing poly and damaged insulation.** The old 6-mil sheeting came out entirely. So did the saturated fiberglass batts. You can't encapsulate over a compromised substrate and expect a durable result. **Step two: install a sealed 20-mil reinforced liner.** We ran a heavy-duty, puncture-resistant encapsulation liner across the entire crawl space floor and up all stem walls, terminating at the sill plate. Every seam was overlapped and sealed with manufacturer-specified tape. Every penetration — pipe boots, post bases, anything passing through the liner — was sealed individually. The liner was mechanically fastened to the stem walls so it can't pull away over time. **Step three: close and seal all foundation vents.** This is the step that surprises some homeowners. In a hot-humid climate like Middle Tennessee, open foundation vents are a liability in summer, not a benefit. We sealed each vent with rigid foam insulation and foam-sealed the perimeter, converting the crawl space from a vented to a sealed, conditioned-adjacent assembly — consistent with current building science guidance for Climate Zone 4A. **Step four: install a dedicated crawl space dehumidifier.** A properly sealed crawl space still needs active moisture management. We installed a commercial-grade dehumidifier sized for the square footage of the crawl space, with a direct drain line so there's no bucket to empty. It maintains the space and protects the encapsulation investment year-round. Two weeks after completion — with zero changes to the HVAC equipment — the homeowner's thermostat hygrometer was reading 48–52% relative humidity. The air conditioner was cycling normally. The house felt comfortable for the first time all summer. --- ## What to Watch For: When "HVAC Can't Keep Up" Isn't Really an HVAC Problem This job is a good illustration of a pattern we see regularly in Middle Tennessee. A homeowner notices the house feels muggy. The AC seems to be working hard. The natural assumption is that the equipment is failing or undersized. An HVAC contractor — doing their job honestly — looks at the equipment and load calculations, and a bigger system looks like a reasonable answer. But in a hot-humid climate, **an air conditioner that's maintaining temperature while losing the humidity battle is often fighting a moisture source it was never designed to address.** The latent load is coming from somewhere the equipment can't see. Common sources include: - **An unencapsulated or poorly encapsulated crawl space** — by far the most common culprit in older Middle Tennessee homes with vented crawl spaces. - **Open or leaking foundation vents** pulling in saturated summer air. - **Damaged or missing vapor control** under a slab addition or in a finished basement. - **Air sealing failures** at the rim joist or band joist that let outdoor air bypass the thermal envelope. Before you authorize a new HVAC unit, it's worth having your crawl space inspected. Crawl space encapsulation in Murfreesboro is a fraction of the cost of new HVAC equipment — and it solves the actual problem. A proper encapsulation also protects your subfloor framing, discourages pest activity, and can improve the performance of any HVAC system you already have. If your home was built before 2000 and has a vented crawl space, there's a reasonable chance the vapor control underneath you is inadequate by today's standards — even if it looks like something is down there. --- *Names and details are illustrative; the problem and fix reflect real jobs we do.* If your home feels muggy despite a running AC, don't replace equipment before you know what's underneath. Call us at {{phone}} — we'll get in the crawl space and give you a straight answer. --- Canonical URL: https://crawl-space-encapsulation-murfreesboro.com/pages/what-we-found-when-a-murfreesboro-homeowner-s-hvac-couldn-t-keep-up-in-july