"You shouldn't buy a home unless you have a thermal infrared inspection",
Department of Energy, Channel 7 News
How Thermographic Inspections Work
Thermography measures surface temperatures by using infrared video and still cameras. These tools see light that is in the heat spectrum. Images on the video or film record the temperature variations of the building's skin, ranging from white for warm regions to black for cooler areas. The resulting images help the inspector determine whether insulation is needed. They also serve as a quality control tool, to ensure that insulation has been installed correctly.
A thermographic inspection is either an interior or exterior survey. The energy inspector decides which method would give the best results under certain weather conditions. Interior scans are more common, because warm air escaping from a building does not always move through the walls in a straight line. Heat loss detected in one area of the outside wall might originate at some other location on the inside of the wall. Also, it is harder to detect temperature differences on the outside surface of the building during windy weather. Because of this difficulty, interior surveys are generally more accurate because they benefit from reduced air movement.
Thermography uses specially designed infrared video or still cameras to make images (called thermograms) that show surface heat variations. Infrared scanning allows energy inspectors to check the effectiveness of insulation in a building's construction. The resulting thermograms help inspectors determine whether a building needs insulation and where in the building it should go. Because wet insulation conducts heat faster than dry insulation, thermographic scans of roofs can often detect roof leaks.
In addition to using thermography during an energy inspection, you should have a scan done before purchasing a house; even new houses can have defects in their thermal envelopes. You may wish to include a clause in the contract requiring a thermographic scan of the house. A thermographic scan performed by a certified technician is usually accurate enough to use as documentation in court proceedings.
Preparing for a Thermographic Inspection
To prepare for an interior thermal scan, the homeowner should take steps to ensure an accurate result. This may include moving furniture away from exterior walls and removing drapes. The most accurate thermographic images usually occur when there is a large temperature difference (at least 20°F [14°C]) between inside and outside air temperatures. In northern states, thermographic scans are generally done in the winter. In southern states, however, scans are usually conducted during warm weather with the air conditioner on.
Detecting Air Leaks
You may already know where some air leakage occurs in your home, such as an under-the-door draft, but you'll need to find the less obvious gaps to properly air seal your home. For a thorough and accurate measurement of air leakage in your home, hire a qualified technician to conduct an energy inspection. Fusion's energy inspections use thermography—or infrared scanning—to detect thermal defects and air leakage in building envelopes.
RESNET, Certified Home Energy Surveys
A Home Energy Survey evaluates how energy efficient a home is by assessing the amount of energy it consumes. Based upon this report, a professional home energy survey will to point out problems and suggest measures that a homeowner can take to make the home more energy efficient, thereby potentially saving the owner a significant amount of money over time. A home energy survey will also assess the efficiency of the home's heating and cooling systems and present ways by which hot water and electricity can be better conserved.
A home's energy efficiency can be diagnosed through a variety of techniques. For example, in conducting a Diagnostic Survey, a professional home energy surveyor may use a blower door to measure the extent of leaks in the building envelope or an infrared camera to pinpoint hard-to-detect areas of air infiltration and missing insulation.
When creating an energy-efficient, airtight home through air sealing techniques, it's very important to consider ventilation. Unless properly ventilated, an airtight home can seal in indoor air pollutants. Ventilation also helps control moisture—another important consideration for a healthy, energy-efficient home.
Purpose of Ventilation
Your home needs ventilation—the exchange of indoor air with outdoor air—to reduce indoor pollutants, moisture, and odors. Contaminants such as formaldehyde, volatile organic compounds, and radon can accumulate in poorly ventilated homes, causing health problems. Excess moisture in a home can generate high humidity levels. High humidity levels can lead to mold growth and structural damage to your home.
To ensure adequate ventilation, the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) says that a home's living area should be ventilated at a rate of 0.35 air changes per hour or 15 cubic feet per person per minute, whichever is greater.
There are three basic ventilation strategies:
Natural Ventilation Uncontrolled air movement into a home through cracks, small holes, and vents, such as windows and doors. Not recommended for tightly sealed homes. Whole-House Ventilation Controlled air movement using one or more fans and duct systems. Spot Ventilation Controlled air movement using localized exhaust fans to quickly remove pollutants and moisture at their source. Typically used in conjunction with one of the other strategies.
Properly controlling moisture in your home will improve the effectiveness of your air sealing and insulation efforts, and vice versa. Thus, moisture control contributes to a home's overall energy efficiency.
The best strategy for controlling moisture in your home depends on your climate and how your home is constructed. Before deciding on a moisture control strategy for your home, you may first want to understand how moisture moves through a home.
Moisture control strategies typically include the following areas of a home:
Attics Foundation Basement Crawl space Slab-on-grade floors Walls.
In most U.S. climates, you can use vapor diffusion retarders in these areas of your home to control moisture. Proper ventilation should also be part of a moisture control strategy.
Elements of an Energy Efficient House
Designing and building an energy-efficient home that conforms to the many considerations faced by home builders can be a challenge. However, any house style can be made to require relatively minimal amounts of energy to heat and cool, and be comfortable and healthy. It's easier now to get your architect and builder to use improved designs and construction methods. Even though there are many different design options available, they all have several things in common: a high R-value, tightly sealed thermal envelope; controlled ventilation; and lower than usual heating and cooling bills.
Some designs are more expensive to build than others, but none of them need to be extremely expensive to construct. Recent technological improvements in building elements and construction techniques, and heating, ventilation, and cooling systems, allow most modern energy saving ideas to be seamlessly integrated into any type of house design without sacrificing comfort, health, or aesthetics. The following is a discussion of the major elements of energy-efficient home design and construction systems.
The Thermal Envelope
A "thermal envelope" is everything about the house that serves to shield the living space from the outdoors. It includes the wall and roof assemblies, insulation, windows, doors, finishes, weather-stripping, and air/vapor retarders. Specific items to consider in these areas are described below.
Wall and Roof Assemblies
There are several alternatives to the conventional "stick" (wood stud) framed wall and roof construction now available and growing in popularity. They include:
•Optimum Value Engineering (OVE)
This is a method of using wood only where it does the most work, thus reducing costly wood use and saving space for insulation. However, workmanship must be of the highest order since there is very little room for construction errors.
•Structural Insulated Panels (SIP)
These are generally plywood or oriented strand board (OSB) sheets laminated to a core of foam board. The foam may be 4 to 8 inches thick. Since the SIP acts as both the framing and the insulation, construction is much faster than OVE or it's older counterpart "stick-framing." The quality of construction is often superior too since there are fewer places for workers to make mistakes.
•Insulating Concrete Forms (ICF)
These often consist of two layers of extruded foam board (one inside the house and one outside the house) that act as the form for a steel reinforced concrete center. This is the fastest and least likely technique to have construction mistakes. Such buildings are also very strong and easily exceed code requirements for tornado or hurricane prone areas.
An energy-efficient house has much higher insulation R-values than required by most local building codes. For example, a typical house in New York State might have haphazardly installed R-11 fiberglass insulation in the exterior walls and R-19 in the ceiling, and the floors and foundation walls may not be insulated. A similar, but well-designed and constructed house's insulation levels would be in the range of R-20 to R-30 in the walls (including the foundation) and R-50 and R-70 in the ceilings. Carefully applied fiberglass batt or roll, wet-spray cellulose, or foam insulations will fill wall cavities completely.
Air / Vapor Retarders
These are two things that sometimes can do the same job. How to design and install them depends a great deal on the climate and what method of construction is chosen. No matter where you are building, water vapor condensation is a major threat to the structure of a house. In cold climates, pressure differences can drive warm, moist indoor air into exterior walls and attics. It condenses as it cools. The same can be said for very Southern climates, just in reverse. As the humid outdoor air enters the walls to find cooler wall cavities it condenses into liquid water. This is the main reason why some of the old buildings in the South that have been retrofitted with air conditioners now have mold and rotten wood problems.
Regardless of your climate, it is important to minimize water vapor migration by using a carefully designed thermal envelope and sound construction practices. Any water vapor that does manage to get into the walls or attics must be allowed to get out again. Some construction methods and climates lend themselves to allowing the vapor to flow towards the outdoors. Others are better suited to letting it flow towards the interior so that the house ventilation system can deal with it.
The Airtight Drywall Approach and the Simple CS system are other methods to control air and water vapor movement in a residential building. These systems rely on the nearly airtight installation of sheet materials such as drywall or gypsum board on the interior as the main barrier, and carefully sealed foam board and/or plywood on the exterior.
Foundations and Slabs
Foundation walls and slabs should be at least as well insulated as the living space walls. Uninsulated foundations have a negative impact on home energy use and comfort, especially if the family uses the lower parts of the house as a living space. Also, appliances that supply heat as a by-product, such as domestic hot water heaters, washers, dryers, and freezers, are often located in basements. By carefully insulating the foundation walls and floor of the basement, these appliances can assist in the heating of the house.
The typical home loses over 25% of its heat through windows. Since even modern windows insulate less than a wall, in general an energy-efficient home in heating dominated climates should have few windows on the north, east, and west exposures. A rule-of-thumb is that window area should not exceed 8-9% of the floor area, unless your designer is experienced in passive solar techniques. If this is the case, then increasing window area on the southern side of the house to about 12% of the floor area is recommended. In cooling dominated climates, its important to select east, west, and south facing windows with low solar heat gain coefficients (these block solar heat gain). A properly designed roof overhang for south-facing windows is important to avoid overheating in the summer in most areas of the continental United States. At the very least, Energy Star rated windows or their equivalents, should be specified according to the Energy Star regional climatic guidelines.
In general, the best sealing windows are awning and casement styles since these often close tighter than sliding types. Metal window frames should be avoided, especially in cold climates. Always seal the wall air/vapor diffusion retarder tightly around the edges of the window frame to prevent air and water vapor from entering the wall cavities.
A well-constructed thermal envelope requires that insulating and sealing be precise and thorough. Sealing air leaks everywhere in the thermal envelope reduces energy loss significantly. Good air-sealing alone may reduce utility costs by as much as 50% when compared to other houses of the same type and age. Homes built in this way are so energy-efficient that specifying the correct sizing heating/ cooling system can be tricky. Rules-of-thumb system sizing is often inaccurate, resulting in oversizing and wasteful operation.
Since an energy-efficient home is tightly sealed, it's also important and fairly simple to deliberately ventilate the building in a controlled way. Controlled, mechanical ventilation of the building reduces air moisture infiltration and thus the health risks from indoor air pollutants, promotes a more comfortable atmosphere, and reduces the likelihood of structural damage from excessive moisture accumulation.
A carefully engineered ventilation system is important for other reasons too. Since devices such as furnaces, water heaters, clothes dryers, and bathroom and kitchen exhaust fans exhaust air from the house, it's easier to depressurize a tight house if all else is ignored. Natural draft appliances, such as water heaters, wood stoves, and furnaces may be "back drafted" by exhaust fans and lead to a lethal build-up of toxic gases in the house. For this reason it's a good idea to only use "sealed combustion" heating appliances wherever possible and provide make-up air for all other appliances that can pull air out of the building.
Heat recovery ventilators (HRV) or energy recovery ventilators (ERV) are growing in use for controlled ventilation in tight homes. These devices salvage about 80% of the energy from the stale exhaust air and then deliver that energy to the fresh entering air by way of a heat exchanger inside the device. They are generally attached to the central forced air system, but they may have their own duct system.
Other ventilation devices such as through-the-wall and/or "trickle" vents may be used in conjunction with an exhaust fan. They are, however, more expensive to operate and possibly more uncomfortable to use since they have no energy recovery features to pre-condition the incoming air. Uncomfortable incoming air can be a serious problem if the house is in a northern climate, and they can create moisture problems in humid climates. This sort of ventilation strategy is recommended only for very mild to low humidity climates.
Heating and Cooling Requirements
Houses incorporating the above elements should require relatively small heating systems (typically less than 50,000 BTU/hour even for very cold climates). Some have nothing more than sunshine as the primary source of heat energy. Common choices for auxiliary heating include radiant in-floor heating from a standard gas-fired water heater, a small boiler, furnace, or electric heat pump. Also, any common appliance that gives off "waste" heat can contribute significantly to the heating requirements for such houses. Masonry, pellet, or wood stoves are also options, but they must be operated carefully to avoid "back drafting."
If an air conditioner is required, a small (6,000 BTU/ hour) unit can be sufficient. Some designs use only a large fan and the cooler evening air to cool down the house. In the morning the house is closed up and it stays comfortable until the next evening.
Beginning a Project
Houses incorporating the above features have many advantages. They feel more comfortable since the additional insulation keeps the interior wall temperatures more stable. The indoor humidity is better controlled, and drafts are reduced. A tightly sealed air/vapor retarder reduces the likelihood of moisture and air seeping through the walls. They are also very quiet because of the extra insulation and tight construction.
There are some potential drawbacks. They may cost more and take longer to build than a conventional home, especially if your builder and the contractors are not familiar with them. Even though their structure may differ only slightly from conventional homes, your builder and the contractors may be unwilling to deviate from what they've always done before. They may need education or training if they have no experience with these systems. Because some systems have thicker walls than a "typical" home, they may require a larger foundation to provide the same floor space.
Before beginning a home-building project, carefully evaluate the site and its climate to determine the optimum design and orientation. You may want to take the time to learn how to use some of the energy related software programs that are available to assist you. Prepare a design that accommodates appropriate insulation levels, moisture dynamics, and aesthetics. Decisions regarding appropriate windows, doors, and heating, cooling and ventilating appliances are central to an efficient design. Also evaluate the cost, ease of construction, the builder's limitations, and building code compliance. Some schemes are simple to construct, while others can be extremely complex and thus expensive.
An increasing number of builders are participating in the federal government's Building America and Energy Star Homes programs, which promote energy-efficient houses. Many builders participate so that they can differentiate themselves from their competitors. Construction costs can vary significantly depending on the materials, construction techniques, contractor profit margin, experience, and the type of heating, cooling and ventilation system chosen. However, the biggest benefits from designing and building an energy-efficient home are its superior comfort level and lower operating costs. This relates directly to an increase in its real-estate market value.
A well-designed landscape not only can add beauty to your home but it also can reduce your heating and cooling costs. On average, landscaping for energy efficiency provides enough energy savings to return an initial investment in less than 8 years. The energy-conserving landscape strategies you use should depend on which region you live in.
The Washington D.C.metropolitan region is in a temperate region. The U.S. Department of energy recommends the following general guidelines for temperate regions.
Maximize warming effects of the sun in the winter. Maximize shade during the summer. Deflect winter winds away from buildings. Funnel summer breezes toward the home.
Landscaping and Your Microclimate
The climate immediately surrounding your home is called its microclimate. When landscaping for energy efficiency, it's important to consider your microclimate along with your regional climate.
Your home's microclimate may receive more sun, shade, wind, rain, snow, moisture, and/or dryness than average local conditions. If your home is located on a sunny southern slope, it may have a warm microclimate, even if you live in a cool region. Or, even though you live in a hot-humid region, your home may be situated in a comfortable microclimate because of abundant shade and dry breezes. Nearby bodies of water may increase your site's humidity or decrease its air temperature.
Microclimatic factors also help determine what plants may or may not grow in your landscape.
Solar heat absorbed through windows and roofs can increase your air conditioner use. Incorporating shading concepts into your landscape design can help reduce this solar heat gain, reducing your cooling costs.
Shading and evapotranspiration (the process by which a plant actively moves and releases water vapor) from trees can reduce surrounding air temperatures as much as 9° F (5°C). Because cool air settles near the ground, air temperatures directly under trees can be as much as 25°F (14°C) cooler than air temperatures above nearby blacktop.
Using shade effectively requires you to know the size, shape, and location of the moving shadow that your shading device casts. Also, homes in cool regions may never overheat and may not require shading. Therefore, you need to know what landscape shading strategies will work best in your regional climate and your microclimate.
Trees can be selected with appropriate sizes, densities, and shapes for almost any shading application. To block solar heat in the summer but let much of it in during the winter, use deciduous trees. To provide continuous shade or to block heavy winds, use dense evergreen trees or shrubs.
Deciduous trees with high, spreading crowns (i.e., leaves and branches) can be planted to the south of your home to provide maximum summertime roof shading. Trees with crowns lower to the ground are more appropriate to the west, where shade is needed from lower afternoon sun angles. Trees should not be planted on the southern sides of solar-heated homes in cold climates because the branches of these deciduous trees will block some winter sun.
Although a slow-growing tree may require many years of growth before it shades your roof, it will generally live longer than a fast-growing tree. Also, because slow-growing trees often have deeper roots and stronger branches, they are less prone to breakage by windstorms or heavy snow loads. Slow-growing trees can also be more drought resistant than fast-growing trees.
A 6-foot to 8-foot (1.8-meter to 2.4-meter) deciduous tree planted near your home will begin shading windows the first year. Depending on the species and the home, the tree will shade the roof in 5–10 years. If you have an air conditioner, shading the unit can increase its efficiency by as much as 10%.
Trees, shrubs, and groundcover plants can also shade the ground and pavement around the home. This reduces heat radiation and cools the air before it reaches your home's walls and windows. Use a large bush or row of shrubs to shade a patio or driveway. Plant a hedge to shade a sidewalk. Build a trellis for climbing vines to shade a patio area.
Vines can also shade walls during their first growing season. A lattice or trellis with climbing vines, or a planter box with trailing vines, shades the home's perimeter while admitting cooling breezes to the shaded area.
Shrubs planted close to the house will fill in rapidly and begin shading walls and windows within a few years. However, avoid allowing dense foliage to grow immediately next to a home where wetness or continual humidity are problems. Well-landscaped homes in wet areas allow winds to flow around the home, keeping the home and its surrounding soil reasonably dry.
Properly selected and placed landscaping can provide excellent wind protection, or windbreaks, which will reduce heating costs considerably. Furthermore, the benefits from these windbreaks will increase as the trees and shrubs mature.
To use a windbreak effectively, you need to know what landscape strategies will work best in your regional climate and your microclimate.
Basically, a windbreak can lower the wind chill near your home. Wind chill occurs when wind speed lowers the outside temperature. For example, if the outside temperature is 10°F (-12°C) and the wind speed is 20 miles per hour (32 kilometers per hour), the wind chill is -24°F (-31°C). A windbreak will reduce wind speed for a distance of as much as 30 times the windbreak's height. But for maximum protection, plant your windbreak at a distance from your home of two to five times the mature height of the trees.
The best windbreaks block wind close to the ground by using trees and shrubs that have low crowns. Dense evergreen trees and shrubs planted to the north and northwest of the home are the most common type of windbreak. Trees, bushes, and shrubs are often planted together to block or impede wind from ground level to the treetops. Evergreen trees combined with a wall, fence, or earth berm (natural or man-made walls or raised areas of soil) can deflect or lift the wind over the home. Be careful not to plant evergreens too close to your home's south side if you are counting on warmth from the winter sun.
If snow tends to drift in your area, plant low shrubs on the windward side of your windbreak. The shrubs will trap snow before it blows next to your home.
In addition to more distant windbreaks, planting shrubs, bushes, and vines next to your house creates dead air spaces that insulate your home in both winter and summer. Plant so there will be at least 1 foot (30 centimeters) of space between full-grown plants and your home's wall.
Summer winds, especially at night, can have a cooling effect if used for home ventilation. However, if winds are hot and your home is air conditioned all summer, you may want to keep summer winds from circulating near your home.
Department of Energy, Energy Star Information and Publications in .pdf format