Green remodeling covers a broad and diverse spectrum of topics that could not possibly be addressed (in entirety) here. For our purposes, we will address primarily basic building science and building testing, indoor air/environmental quality, energy efficiency (including Energy Star) and recycling options. For a more in-depth discussion, see Residential Energy by Krigger and Dorsi, chapters 1, 2, 3 and 10.
Building Science Overview
Building science is the study of the building and the interaction of its component systems, combined with an understanding of heat, water and air movement, and how they directly impact the health and safety of the occupants.
Heat: Energy in the form of heat travels in three ways: radiation, conduction and convection. Additionally, heat always travels from a warm area to a cold area, no matter the method of travel.
Moisture: Moisture in the home has two components: gas (vapor) and liquid. Liquid (water) will travel from wet area to dry area. It can be pulled by gravity as it flows down an incline or by capillary action as it wicks up a porous material, like a wood stud or concrete foundation. Water intrusion can be damaging to the home, causing wood rot and mold.
As a gas, water vapor is lighter than air, and the water molecules are smaller than that of air, so while an area may be sealed to air infiltration, it still may be vulnerable to vapor intrusion. Warm air can hold more water than cooler air. Relative humidity (rh) is a measurement of how saturated the air is as a volume of air to its percentage of water vapor in that same air. When air is completely saturated, it has an rh of 100 percent. For example, if the outside air is 91 F and 50 percent rh and the temperature of the air drops to 70 F (without removing any moisture), the rh will increase to 100 percent. The air has contracted in volume because of the drop in temperature, but the amount of water vapor in that same air has not. Even though the amount of moisture is the same, the air is now completely saturated.
Air: Air will move from areas of higher density (pressure) to areas of lower pressure. Most homes are naturally ventilated, meaning that air infiltrates the home through the cracks and holes that exist in the home’s structure. The air exchange rate is called Air Change per Hour (ACH) and can range from a very tight 0.25 ACH to a very leaky home at 1.25 ACH. Air change can be computed using a blower door test.
The American Society of Heating, Refrigeration and Air Conditioning Engineers uses a design specification of eight complete air changes per 24 hour period when designing heating/cooling loads for HVAC systems.
Air can be exchanged though the home by a number of modes. The stack effect is caused by the convection of heated air from the lower parts of the home up through and passing out of the home through the ceiling, attic and various leakage paths provided. The larger the total area of these cracks and holes, the higher the exchange rate. Wind can cause a pressure difference across the house, causing air to be sucked out of the home on the low pressure side. Any holes in the envelope will allow air to pass.
The home’s flues, chimney and other exhaust systems are also factors that add to the exchanging of the home’s air.
Building Testing Processes
When looking to the testing process on buildings, most people think it will identify problems with doors, windows and insulation. Generally speaking, this is a good place to look, but in most cases there are a lot of other areas that will pay back faster and cost a lot less to correct.
When testing a home, start with a blower door test to locate areas of air infiltration. With this test you will probably find there are many other sources of infiltration besides windows and doors—for example, the rim joist, floor joist pockets in the basement and second floor, and attic access panels. Other areas where you may find significant leakage are vent fans, recessed lighting, and pipe or wire penetrations from the top plates into the attic. All these areas can be sealed fairly quickly and inexpensively. Once air sealing of these areas is conducted, air infiltration will be significantly reduced, and the home’s comfort will change for the better.
A blower door test will provide the homeowner with information on how many air changes per hour their home has. The average 30-year-old home will probably test at 1.0 ACH or more. The goal of air sealing is to get it under 0.45 ACH. At 0.45 ACH, the homeowner should start thinking about a heat or energy recovery ventilator (HRV/ERV). This system will introduce fresh, filtered air in a controlled fashion instead of letting the air enter in an uncontrolled fashion all over the home. At 0.35 ACH, a home is getting “tight.” A home can be tighter than that, but the homeowner will have a longer return on investment.
There are other mechanical systems within the home that can be tested and measured, such as the efficiency of the furnace, water heater, appliances, light fixtures and plumbing fixtures. These items can be tested then repaired or replaced by assembling a list, starting with the worst ones and moving up the list as the budget allows.
Indoor Air Quality
A green remodeling component is important to the health and well-being of the occupants, and part of the quality of comfort is indoor air quality (IAQ). The tightening of a home to reduce uncontrolled air infiltration and increase energy efficiency might create an environment that could be unhealthy for its occupants.
Indoor pollution sources that release gases or particles into the air are the primary cause of indoor air quality problems in homes. Though a home is more energy-efficient due to sealing, inadequate ventilation can increase indoor pollutant levels by not bringing in enough outdoor air to dilute emissions from indoor sources and by not carrying indoor air pollutants out of the home. High temperatures and humidity levels within the home can also increase concentrations of some pollutants.
Remodelers, when making energy-efficient improvements in a home, must consider that if too little outdoor air enters a home, pollutants can accumulate to levels that can pose health and comfort problems. Unless a mechanical means of ventilation is introduced into homes that are designed and constructed to minimize the amount of outdoor air that can “leak” in and out of the home, indoor pollutant levels may be higher.
There are three basic strategies to follow to improve indoor air quality:
- Control the source—eliminating the pollutants or reducing their emissions.
- Improve the ventilation—increasing the amount of fresh air introduced into the home in a controlled manner.
- Clean the air—filtering particles such as dust, mold spores, pollen and pet dander from the air.
Dumpster debris sorting: Laws regarding the sorting of construction and demolition waste may have been put in place in your state or community. Check with your hauler and verify what is—and is not—acceptable for
Reusing materials: Stripping nails from 2x material may not be very practical on a cost to value basis; however, saving 4x and larger sized beams can be a practical way to save time, money/profit and landfill space.
ReStores: Remove appliances, cabinets, plumbing, lighting fixtures and even carpets with as little damage as possible so that they can be donated to a local Habitat for Humanity ReStore or other recycling facility. This may result in a tax deduction for you or your client. In some cases, ReStore may conduct the demolition and remove reusable material. This function may also be contracted out to specialty contractors.
Selecting Sustainable Products
A green material is considered something that uses minimal energy and resources to support long-term sustainable use of that product with minimal waste or contamination of earth, air, water and other resources.
“Greenwashing” is calling something green that may not be truly green, but has green aspects to it. Simply because something uses recycled material does not necessarily make it green. Be cautious of marketing strategies that mislead. Another example is something that is perhaps relatively inexpensive to manufacture or produce using natural materials but has high transportation costs; thus, it is not a green product, although it may have green attributes. |QR
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