Murfreesboro Crawl Space Encapsulation: HVAC Uncovers Hidde…

By The Murfreesboro Crawl Space Encapsulation Team — crawl space encapsulation professionals serving Murfreesboro, TN.

---

The Call That Started It All

It was a routine summer HVAC tune-up. A homeowner near the Blackman Road corridor — living in a 2003-built two-story with a vented block-wall crawl space — had scheduled the visit just to make sure the system was ready for another Tennessee summer.

The HVAC technician did what good technicians do: he went under the house.

What he found had nothing to do with refrigerant charge or coil cleanliness. Heavy condensation was forming on the exterior of the flex duct runs throughout the crawl space. Water was beading on the outside of the supply ducts and dripping onto the ground. And the kraft-faced fiberglass batt insulation that had been stapled between the floor joists — original to the 2003 construction — had detached entirely. It was lying in damp piles on the dirt floor.

The homeowner had no idea. The house felt fine upstairs. The AC was cooling. Nothing had triggered an alarm. But underneath the living space, conditions had quietly deteriorated for who knows how long.

The HVAC tech made the right call: he told the homeowner this wasn't a duct problem. He recommended they contact a crawl space specialist before anyone touched a single duct. That's when they called us.

---

What We Found on Site

When our crew arrived and did a full site assessment, the picture came together quickly. This is a construction profile we see constantly in Rutherford County — early-2000s growth subdivisions built with vented crawl space foundations, open block-wall vents, and flex duct HVAC distribution. It was code-compliant at the time. It also creates conditions that work against you every June, July, and August.

Here's what was happening:

The three open foundation vents were doing exactly what they were designed to do — pulling in outdoor air. In a Murfreesboro summer, that outdoor air routinely carries relative humidity above 70%. When that hot, moisture-laden air entered the crawl space and contacted the exterior surface of the supply ducts — which are chilled by the conditioned air passing through them — it hit its dew point. Condensation formed immediately. Every day the AC ran, the ducts sweated.

The same elevated humidity had saturated the kraft-faced fiberglass batts over time. Fiberglass batt insulation between floor joists relies on a friction fit to stay in place. Once the facing absorbed enough moisture, the batts lost their grip and fell. There was no ground cover — bare dirt — which was contributing additional ground moisture vapor to the air inside the crawl space. There was no mechanical dehumidification of any kind.

The duct runs themselves, once we inspected them carefully, were structurally intact. No tears, no disconnected sections. The condensation hadn't yet caused duct failure. But left unaddressed, it would have — and mold colonization of the fallen insulation and subfloor assembly was already a real risk.

The root cause was not the ducts. It was never the ducts. It was the vented crawl space drawing in unconditioned summer air with no way to manage the resulting humidity.

---

How We Fixed It: Full Crawl Space Encapsulation

The resolution was a complete crawl space encapsulation — converting the vented, uncontrolled space into a conditioned, sealed environment.

Here's what the scope of work included:

20-mil reinforced liner installation. We ran a heavy-duty, reinforced polyethylene liner across the entire crawl space floor and up the stem walls, lapping it and sealing it at the wall-floor transition. This is not a standard 6-mil vapor barrier. The 20-mil liner is puncture-resistant, rated for long-term ground contact, and creates a true moisture barrier between the soil and the conditioned space above.

Foundation vent sealing. All three open foundation vents were sealed with rigid foam insulation board and sealed at the perimeter with spray foam. Vented crawl spaces and encapsulation are fundamentally incompatible — you cannot condition a space that is continuously exchanging air with the outdoors.

Rim joist air sealing. We air-sealed penetrations and gaps at the rim joist with two-component spray foam. The rim joist is one of the most significant air-leakage pathways in a crawl space foundation. Closing it is essential to making the conditioned envelope work.

Crawl space dehumidifier with condensate drain. A correctly sized, purpose-built crawl space dehumidifier was installed and plumbed with a condensate drain line to a suitable discharge point. This unit is designed for the low-clearance, high-humidity environment of a crawl space — it's not a portable box-store unit. It maintains relative humidity at or below 55%, which is well below the threshold at which condensation, mold growth, and wood deterioration become concerns.

Fallen insulation removal. The detached fiberglass batts were removed and disposed of. Once the crawl space is conditioned, between-joist batt insulation is no longer the appropriate thermal strategy — the insulation boundary shifts to the stem walls, which are now lined and part of the conditioned envelope. Leaving the old batts in place would have created a debris and moisture trap.

After the encapsulation was complete, we re-inspected the duct runs. No duct repair was required. With ambient humidity controlled, the dew-point differential that had been causing condensation was eliminated. The ducts were dry. The HVAC tech's instinct had been exactly right.

---

What to Watch For: A Note for Murfreesboro Homeowners

If your HVAC technician flags sweating ducts or fallen insulation during a summer service call, pay attention — but don't let anyone sell you duct repairs as the fix.

Condensation on crawl space ductwork is almost never a duct problem. It is a humidity problem.

In a vented crawl space in Middle Tennessee, summer humidity routinely overwhelms any passive ventilation strategy. The outdoor air coming through those foundation vents is warmer and wetter than the conditioned air inside your supply ducts. Physics does the rest. The solution is to eliminate the vented crawl space condition entirely — to encapsulate the space, seal it from outdoor air, and mechanically control the humidity inside it.

This is especially true for homes built in Rutherford County during the early-2000s growth boom. Vented block-wall crawl spaces with flex duct distribution are extremely common in that construction era. If your home fits that profile and you haven't had the crawl space evaluated, a summer tune-up is a good time to ask your HVAC tech to take a look underneath.

Crawl space encapsulation in Murfreesboro addresses the root cause. It protects your duct system, your floor structure, your insulation, and your indoor air quality — all at once.

---

Names and details are illustrative; the problem and fix reflect real jobs we do.

If your HVAC tech found something concerning under your house — or if you just want to know what's going on down there — give The Murfreesboro Crawl Space Encapsulation Team a call at (629) 201-4952. We'll assess the space honestly and walk you through exactly what it needs.