The Over-Engineered Attic

Years ago I was called out to evaluate a moldy house in coastal South Carolina.

The walls, both interior & exterior, were covered in a thin coating of mold growth. The homeowners would clean their walls with a bleach water solution, and within just a few days or even a week the walls would have visible growth on them again.

The homeowner had just recently purchased the property, a 1950's constructed single family "ranch" style home on a dirt crawlspace.

When the homeowner purchased the home it had a large package style heat pump AC, that fed ductwork into the crawlspace. The homeowner removed that existing system & installed a new split AC system with the new air handler mounted in his attic. The new ductwork was routed to a single centrally located return air assembly in a ceiling, and supply vents that fed each room of the house.

The homeowner also had the attic insulated, as the existing insulation was barely covering the 2x6 rafters.

As result of the AC's air handler being installed in an airtight, over insulated attic in the summer of eastern SC, the exterior of the AC developed a large amount of condensation, as well as the interior lined sheet metal ductwork attached to it. The attic's temperature around noon was well over 125 degrees Fahrenheit.

So the homeowners solution to this was to add an attic exhaust fan. When 1 fan didn't fix it, he decided that the attic exhaust fans' 3000 CFM clearly wasn't enough, so logically he added a 2nd attic exhaust fan. When the problem persisted, it was at this point that he started looking for professional guidance.

The first contractor that showed up, suggested adding a 3rd attic fan, or using spray foam on the AC and ductwork. The homeowner opted to have a spray foam contractor come in, remove the insulation around the HVAC system, and he then encapsulated the ductwork & air handler with spray foam approximately 3" thick. So now he couldn't see the condensation, But now the walls in his house were developing mold growth. (the bottom of the air handler, which wasn't insulated, dripped water into the pan)

When we finally were called out, We quickly identified that the soffit vents were blocked off with blown insulation & there was no ridge vent to let heat escape.

The walls of the house were covered with a light coating of mold growth, despite having been cleaned a week prior to our arrival.

We explained that the exhaust fans were pulling a strong negative pressure in the attic, which in turn was drawing on the interior walls of the house, scavenging air from the crawlspace through the wall cavities into the attic. This hot humid air was condensing on the cooled interior surfaces of the house, such as the walls.

Our remediation plan started with removal of the remaining blown & batted insulation from the attic. The recommendation of the installation of plastic baffles to allow outside airflow in from the soffit vents, around & over the insulation & into the attic.

We recommended the installation of a new roof with a properly installed ridge vent, and removal of the newly installed attic exhaust fans. We recommended the removal of the spray foam insulation from the air handler to allow for future repair & serviceability along with accessibility for air duct cleaning.

We decided to leave the spray foam on the branch lines and most of the main plenums. We installed a vapor barrier in the crawlspace to control the moisture from the soil, as well as recommending they install a sump pump & small 90 pint dehumidifier in the crawlspace.

The interior of the house required all the furniture & personal items to be removed from the home & moved into an onsite storage unit, and cleaned & dried prior to being moved into the storage unit while working on the interior of the property.

Once the customers furniture was removed, we recommended removal of drywall from all walls & ceilings in the home, this extended to removal of the kitchen cabinetry, bath tubs & floor coverings as the project progressed.

The house was extensively cleaned & tested for cleanliness upon completion. The holes in the framing allowing electrical & plumbing passage into the house were all sealed with fire rated caulk.

Once the home was completely reconstructed, and properly insulated, the condensation issues in the attic were relieved. The temperatures in the attic were returned to normal, and the house no longer experienced any of the issues previously experienced.

He said that his biggest regret was not just calling us first.