# Crawl Space Encapsulation Murfreesboro: Dehumidifier Fix > A Siegel-area homeowner's dehumidifier ran nonstop and humidity stayed above 70%. We found open vents — here's what proper encapsulation fixed. Call us. Murfreesboro Crawl Space Encapsulation Pros | crawl space encapsulation | Murfreesboro, TN ## The Call: Bills Up, Humidity Still Up A homeowner in a 1990s split-level near Siegel Road reached out in midsummer with a frustrating situation. A contractor had installed a crawl space dehumidifier the previous spring. The unit ran constantly — never cycling off — and the electricity bill had climbed noticeably month over month. Worse, a hygrometer the homeowner had placed in the crawl space still read above 70% relative humidity on the hottest days. They'd already called the original contractor. The answer they got back was essentially a shrug: the machine was working fine, humidity in Middle Tennessee summers is just high, maybe they needed a second unit. That answer didn't sit right. So they called us for a second opinion. This is one of the most common calls we get. And almost every time, the dehumidifier isn't the problem. The crawl space is. --- ## What We Found On Site We pulled the access hatch and went under the house within a few days of that first call. The split-level had a partial crawl space beneath the lower level — typical for that era of construction in Murfreesboro subdivisions. The original builder-installed foundation vents were still in place: six of them, screened with deteriorated fiberglass mesh that had sagged and torn in places. All six were open to outside air. The vapor barrier situation wasn't much better. There was a thin sheet of 6-mil poly on portions of the dirt floor — the kind of material that was standard practice decades ago — but it had no taped seams, wasn't lapped up the stem walls, and had shifted and torn in several spots. Moisture from the ground was moving freely into the air column underneath the house. Here's the core problem, and it's a physics issue as much as a construction one: Murfreesboro sits in a humid continental-subtropical climate. In July and August, outdoor air routinely carries a dew point above 70°F. When that air flows through open foundation vents — which it does, continuously, driven by pressure differentials and wind — it brings an enormous latent moisture load into the crawl space. A standalone dehumidifier, no matter how well-rated, cannot process that volume of incoming moisture. It was, quite literally, trying to dehumidify the outdoors. The unit wasn't undersized for a sealed crawl space. It was catastrophically undersized for the job it was actually being asked to do: condition an open, unencapsulated void connected directly to the outside. Proper **crawl space encapsulation in Murfreesboro** starts with cutting off that moisture pathway entirely. A dehumidifier is a conditioning appliance. It belongs inside a sealed envelope — not at the front lines of a humidity battle with the Tennessee summer. --- ## How We Fixed It The scope of work had three phases, and the sequence matters. **Phase 1 — Seal the foundation vents.** We installed rigid foam vent covers over all six foundation openings and packed the perimeter gaps with hydraulic cement to create an airtight, moisture-resistant seal. No more outside air exchange through the foundation. This step alone changes the entire energy dynamic of the crawl space. **Phase 2 — Install a proper vapor barrier liner.** We removed the old 6-mil poly and replaced it with a 20-mil reinforced liner across the entire crawl space floor, running the material up the stem walls and securing it at the top with mechanical fasteners and tape. Every seam was overlapped and sealed. This liner is the moisture mitigation layer — it blocks ground-source vapor before it ever enters the air column. Think of it as the vapor barrier equivalent of a fully waterproofed shower pan: the membrane has to be continuous and sealed, or it isn't doing its job. **Phase 3 — Right-size the dehumidifier.** With the space now properly sealed, we calculated the actual cubic footage of the conditioned crawl space and specified a new Energy Star-rated dehumidifier sized to that load — not the load of the open outdoors. We also installed a condensate pump to route drainage away from the crawl space automatically, so the unit never needs manual emptying. The result was immediate and measurable. Within the first week, the homeowner reported that the dehumidifier was cycling on and off normally — running for a period, reaching its set point, shutting down. Relative humidity dropped into the 50–55% range and held there. The unit was no longer running at full capacity around the clock. That's what **crawl space encapsulation in Murfreesboro** is supposed to accomplish: a stable, conditioned environment that the mechanical equipment can actually maintain. --- ## What to Watch For in Your Own Crawl Space This job is a useful case study because the original mistake is so common — and so easy to make if you don't understand how crawl space conditioning actually works. **Open or passive foundation vents are not compatible with a dehumidifier-based system.** Full stop. The older building science logic was that cross-ventilation would dry out a crawl space. Modern building science — and decades of real-world performance data in humid climates like Middle Tennessee — shows the opposite is true. Vented crawl spaces in humid climates accumulate moisture; they don't shed it. If you have a dehumidifier in your crawl space and you're noticing any of the following, it's worth having the whole system evaluated: - The unit runs continuously without cycling off - Your electricity bills have increased since installation - You're still reading humidity above 60% on a hygrometer placed in the space - There is visible condensation on floor joists, HVAC ducts, or ductwork insulation - You notice musty odors on the first floor, particularly in rooms directly above the crawl space Any one of these symptoms can point to an encapsulation problem, not a dehumidifier problem. Adding a second unit — or a larger unit — without sealing the space first will only compound the energy waste. The right sequence is always: **seal first, then condition.** A dehumidifier installed into an unencapsulated crawl space isn't doing moisture mitigation. It's doing damage control, indefinitely, at your expense. **Crawl space encapsulation in Murfreesboro** done correctly — sealed vents, continuous 20-mil liner with taped seams lapped up the stem walls, and a properly sized dehumidifier — creates a stable conditioned space that protects your floor structure, your HVAC equipment, your insulation, and the air quality of the living space above. If a previous contractor installed a dehumidifier without sealing your foundation vents first, the encapsulation was never completed. The dehumidifier is working as hard as it can. It just can't win. --- *Names and details are illustrative; the problem and fix reflect real jobs we do.* If your crawl space dehumidifier is running nonstop or your humidity readings won't come down, we'd like to take a look. Call us at {{phone}} to schedule a crawl space assessment in Murfreesboro and the surrounding area. --- Canonical URL: https://crawl-space-encapsulation-murfreesboro.com/pages/the-crawl-space-dehumidifier-that-was-working-too-hard-what-we-found-under-a-sie