IAQ can be affected by microbial contaminants (mold, bacteria), gases (including carbon monoxide, radon, volatile organic compounds), particulates, or any mass or energy stressor that can induce adverse health conditions. Indoor air is becoming an increasingly more concerning health hazard than outdoor air. Using ventilation to dilute contaminants, filtration, and source control are the primary methods for improving indoor air quality in most buildings.
As builders, what can we do to improve air quality, and what can we do to eliminate the causes of indoor air pollution? We've been told for a few years now that we are building homes tighter and tighter, and to some degree that is true. What we have to realize is that as we tighten up the building envelope, we are creating other areas where the envelope can be penetrated if not treated properly. The beginning of a good building envelope starts with the sheathing and the water and vapor barrier. We have recently begun using the Zip Wall System by Huber Engineered Woods, but have successfully used OSB sheathing with a Tyvek Wrap barrier. The key to either system is to make sure your framing crew, or whoever is installing the wrap and tape system, has the appropriate tools, a knowledge of the proper installation of the system, and adequate supervision to guarantee all joints are taped per manufacturer's recommendation. Depending on which system you use, there are also differing opinions on the best details for sealing the windows and the doors. Once again, you need to make sure you know what the manufacturer's recommendations are in this area, and I believe, you need to take a little more time and spend just a little more money to insure that you have these areas sealed beyond those minimum requirements.
The second areas to address are the penetrations through the building envelope. The average home can have anywhere from 20-40 penetrations through the building envelope, depending on how many exterior lights, outlets, hose bibs, condensing units, etc. We are using a product called Quickflash Weatherproofing Products to help to seal these areas prior to installing siding, plaster, or masonry on the exterior of our homes. Quickflash has multiple flashing sizes to accommodate almost every size of penetration for electrical, plumbing, gas, and HVAC systems. When installed properly with your vapor and water barrier, these flashings provide a no caulk friction seal at all penetrations, and give the builder an extra layer of protection against water and air leaks.
Insulation is the next layer of protection we install to seal the envelope. We use a hybrid insulation method, which effectively and efficiently provides excellent energy performance with a lower cost to install compared to an all foam application. The hybrid system involves the use of spray foam at the underside of the roof deck and in all high risk or problem insulation areas like kneewalls, rim joists, cantilevers, overhangs, etc. The walls are then sprayed with cellulose insulation, which is a full cavity application that not only provides an excellent seal for your energy envelope, but consists of 80% recycled materials. Closed cell spray foam has an R value of approximately 6/inch, and the cellulose produces an R value of 3.7/inch. Our typical application with 2x 6 walls produces an R-20 cellulose installation, and an R-30 spray foam attic installation.
In the construction process for many homes, tubs, showers, and fireplaces are installed immediately after rough framing is complete and before insulation is installed. As a result, it is almost impossible to properly install insulation and complete air barriers at exterior walls adjoining tubs and showers. This can lead to convective air flow that circumvents insulation.
The installation of air barriers and insulation in these applications at exterior walls can be achieved with proper planning starting with design. Spraying cellulose or placing batts in the wall cavity, and then installing an air barrier, such as ThermoPly, along with installing polyseal, will effectively eliminate the convective air flow. Make sure the air barriers are in place prior to installing tubs, showers, and fireplaces. Another option would be to fill the cavity around the tub with spray-foam, which acts as both a thermal and air barrier. In any of these cases, the tubs will be much less likely to cause comfort or moisture problems.
All HVAC equipment is sized using the Manual J Residential Load Calculations, with a minimum of 600 sf/ton of air conditioning. "Right Size" HVAC systems ensure efficient operation along with using a 15.0 SEER rated system with variable speed condensing units and an Energy Star rated Programmable Thermostat. Greatly oversized equipment operates less efficiently and costs more than properly sized equipment. For example, oversized cooling systems may not dehumidify the air properly, resulting in cool but "clammy" spaces. When using a spray foam or hybrid insulation system, that eliminates attic ventilation, you will need to bring fresh air to the HVAC system to keep the proper pressurization and to help with air balancing. Make sure that your HVAC contractor is well versed in both Manual J and fresh air ventilation. To improve the indoor air quality, we are now installing an Optional Advanced IEQ System. The Trane CleanEffects Air Cleaner that will be installed in our Parade Home is the most effective whole-house air filtration system available.
- Removes up to 99.98% of allergens from the filtered air.
- Traps particles down to 0.3 microns in size. (A human hair is about 75 microns in diameter.)
- Up to 100 times more effective than a standard 1" filter.
- Delivers cleaner air and more of it.
- Performance has been verified by leading experts at the Harvard School of Public Health
All bathrooms and the utility room have Energy Star rated Panasonic Whisper Quiet ventilation fans to reduce energy consumption and noise, while helping eliminate moisture and odors in the homes. We will implement extensive duct leakage testing, blower door testing, and air balancing to maximize the efficiency of the system. You will need to coordinate your HVAC contractor and your third party duct tester to get the proper air flow and balancing specifications. By implementing duct leakage testing and blower door testing, the home eliminates duct leakage to improve air flow and balances it evenly in all areas.
All Green Homes are required to install Zero or Low VOC Paint and Stains, and in addition, we are installing all of our flooring with similar adhesive products. All cabinets are prefinished at the factory in controlled atmospheres that recapture stain and paint waste for recycling, and filter the exhaust from the finishing application.
While there are a few other small factors that can be incorporated to improve Indoor Air Quality, these are what I consider to be the main contributors, and if these are all addressed properly, your home will combine all of the performance characteristics into a unified system.