Healthy Indoors Magazine
Issue link: https://hi.healthyindoors.com/i/1088111
36 | February 2019 Some Construction and Renovation Woes ©2019 Jeffrey C. May Duct boots: These should be airtight to prevent musty base- ment or crawl space air from flowing up into the room above. Leaky duct boot May Indoor Air Investigations LLC Types of ducts: What about the types of ducts to install? Avoid duct board ducts, please! This material can never be ad- equately cleaned. Panned bays are also problematic, because the joists have been open to construction dust. I have even found mold growth on these joists due to damp conditions prior to installation of the sheet-metal pan. And if panned bays con- tain wires and cross bracing, they can't be properly cleaned. If panned bays must remain a part of a mechanical sys- tem, the metal pan should be opened up, and the framing cleaned and paint-sealed. For very sensitized occupants, consider lining the joists with aluminum flashing and cov- ering the subflooring with foil-laminated sheet foam. The sheet metal pan should be sealed at any joints. Flexible ducts are not as easy to clean as solid metal ducts are. For family with allergies or asthma I recommend either replacing accessible flexible ducts or using solid metal ducts. Location of ducts: In the winter, the temperature of an uninsulated duct located in a crawl space may fall below the dew point of house air. Then moisture can condense within the duct. If dust is present in the duct, mold growth will en- sue. A similar situation can develop in the summer when the crawl-space and duct-surface temperature are below the dew point of house air during humid weather. I 've inspected dozens of newly constructed homes or additions, as well as spaces that were just renovat- ed, and they were full of IAQ problems. Many of these problems started to occur during construction or reno- vation. In this article, I'm going to focus on mechanical systems. In the next article, I will discuss IAQ problems in basements in new construction. Ducts Dirty ducts: I've found an amazing collection of debris in ducts in new homes, including coffee cups, tape, a tape measure, strip flooring, clumps of grout, fiberglass, and even a donut inside a paper bag. One man was even about to move out of his house be- cause of a horrible smell coming from a bedroom supply. Someone had spilled coffee inside the duct, and the cream had gone sour at an elbow in the basement. In another new home, the ducts were in place but the contractor had not installed the filter in the air handler for fear that the expensive (but disposable) filter would get soiled. What is a filter for, I wondered; the ducts and the air handler were full of sawdust and drywall dust. The builder had to pay for an expensive system cleanup. In a third home that was still under construction, sections of rectangular ducts were sitting upright on the basement floor. Workers were sawing wood in the basement, and the ducts were already filled with biodegradable sawdust. I always recommend that workers saw wood outside the house. If weather requires them to saw inside the house, some sort of exhaust system should be in place to filter the sawdust. Sawdust on foundation walls and in ceiling fiberglass inevitably becomes moldy, so insu- lation should be installed and foundation walls HEPA vacuumed after all basement sawing is done. Most of such material inside ducts is biodegradable. If the relative humidity is high enough, mold will grow: a cer- tainty if the sawdust ends up on a cooling coil. Then the system will carry byproducts of this growth into habitable spaces.