To Prevent IAQ Problems, Consider All Home Factors
That was the message provided by Steve Easley, owner of S.C. Easley and Associates, a Danville, CA-based construction consulting firm, in his keynote speech called “Under-standing the House as a System” at the “Energy: It’s Not All You Save” conference.
A former professor of building construction and contracting at Purdue University, Easley is co-host on the Discovery Channel’s weekly program “Michael Holligan’s Your New House”; host of the upcoming “Bob Vila’s EnergyWise Home Project for the Internet”; and spokesperson for the California Energy Commission’s Internet video training series on home energy efficiency. This expert stresses the need to evaluate all the factors in a house that impact IAQ.
He noted that some builders and contractors blame tight homes for increased mold and other problems. But this is not true, he emphasized. You have to consider the driving forces — the temperature differences and pressure differences that cause air movement.
The factors that affect IAQ, stated Easley, are:
1. Ventilation rate;
2. Pollutant source strength;
3. Exposure time; and
4. Individual sensitivity.
“If you build homes that are leaky and drafty, it’s not going to improve IAQ,” he said. Air coming in through leaks brings in moisture, which causes problems such as mold.
Proper air filtration is important, as well as keeping filters clean. The most common service call for hvac equipment is for dirty filters, he remarked. But the efficiency of common furnace filters is very low. “Ninety-nine percent of particulates in the air are less than 1 micron in size.”
Duct sealing should be done if excessive duct leakage is found. Too much leakage in the basement ductwork below the living room floor, for example, can cause the carpeting to act like an air filter, trapping a tremendous amount of dirt.
PROPERLY INSULATED ENVELOPE“Sixty to 80 percent of moisture problems are because of failure in the exterior envelope” of the home, said Easley.
Reviewing the basics, he related that heat goes from warm to cold; moisture goes from wetter to dryer. Anytime you see mold in a house, it’s because of thermal bridging, poor air circulation, and high moisture. If areas of a home are left uninsulated, they will get colder and the relative humidity will be higher. Thus, a corner of a ceiling that has no insulation will attract moisture and you can have mold problems in that corner. If walls are insulated, but there are gaps that are uninsulated, moisture buildup and mold can develop.
Insulation needs to be carefully installed to avoid such problems.
A kraft-backed insulation for the walls is better in colder climates, he said. A polyethylene vapor barrier can trap moisture in walls and cause serious mold problems due to air conditioning in the summer. If thermal bridging occurs and moisture gets in the drywall, it cannot escape.
“A polyethylene vapor barrier works fine for the heating season but not for the cooling season,” Easley remarked. Wall systems should be as tight as possible, but make the insulation breathable, he stated.
He recommended using Tyvek® house wrap on the outside of the structure. This wrap has about 58% permeability, he said. It serves as an air barrier from the outside but allows any water inside to evaporate out.
It’s better to install wiring down the interior walls of the house, rather than the exterior walls, to ensure better insulation, he added.
ENERGY EFFICIENCYIn a breakout session on energy efficiency issues, Easley provided a list of common sense tips, including:
- Provide adequate insulation.
- Make sure insulation is properly installed.
- Control air infiltration.
- Properly size and install the hvac system.
- Eliminate duct leakage.
Leaving areas around ceiling lights in cathedral ceilings without insulation, or leaving corners or areas around windows uninsulated, causes energy loss. These cold spots can also breed mold problems, as mentioned earlier.
He estimates that “20 to 50 percent of hvac systems are oversized.” A load calculation should be done to ensure proper sizing.
If there is ductwork in the attic, all leaks should very definitely be sealed. “Leaky ducts in a hot attic can reduce the efficiency of a SEER 14 system down to SEER 10,” Easley said.
Publication date: 04/01/2002