Home Inspection FYI

Providing Help, Knowledge and Other Useful Information To Home Owners Everywhere

Home Inspection FYI - Providing Help, Knowledge and Other Useful Information To Home Owners Everywhere

Building Orientation for Optimum Energy

Building orientation is the practice of facing a building so as to maximize certain aspects of its surroundings, such as street appeal, to capture a scenic view, for drainage considerations, etc. With rising energy costs, it’s becoming increasingly important for building orientation to capitalize on the Sun’s free energy.

building orientation sun Building Orientation for Optimum Energy

For developers and builders, building orientation of a new home to take advantage of the warmth of the Sun will increase the home’s appeal and marketability.  For homeowners, building orientation will increase their indoor comfort and reduce their energy bills.

Thus, building orientation, along with day-lighting and thermal mass, are crucial considerations of passive solar construction that can be incorporated into virtually any new home design.

Facts and Figures about Building Orientation

  • Many older homes’ designs were oriented through the use of a heliodon, which is a moveable light source used to mimic the Sun’s path that hovered over a small-scale model of a proposed building. Today, mathematical computer models calculate location-specific solar gain and seasonal thermal performance with precision, and have the added ability to rotate and animate a 3D color graphic model of a proposed building orientation design in relation to the Sun’s path.
  • Homeowners may now tap into a specialty market of homes designed to spin on their axis in order to follow the hourly and seasonal path of the Sun. These UFO-shaped homes can spin a full 360 degrees in minutes and are built with unusually tall ceilings and windows for maximum efficiency in powering their solar energy system.
  • While some passive solar features are relatively recent innovations, the practice of orienting a home to the path of the Sun is as old as civilization itself. Examples are numerous, from south-facing doors on Neolithic and ancient Ming Dynasty houses, to the astonishing Pueblo ruins in southwestern Colorado.

The Sun’s True Position and building orientationsolar north Building Orientation for Optimum Energy

Schoolchildren (and most homeowners) will tell you that the Sun rises in the east and sets in the west, and, if this were true, building orientation would be a fairly simple matter. In reality, the sun rises and sets in the east and west only on the autumnal and vernal equinoxes, and something very different happens during the remaining 363 days of the year. The Earth’s tilt causes the Sun to rise and set slightly south of east and west in the winter, and slightly north of east and west in the summer.  This slight angle depends on the time of year and the observer’s distance from the equator.

As a result, the winter sun spends all of its time in the southern sky, and the summer sun spends all of its time in the northern sky. In the Southern Hemisphere, all of these directions are reversed, so the winter sun rises and sets in the northeast and northwest, respectively, and the summer sun rises and sets in the southeast and southwest, respectively.

How the Sun’s Variations in Position Can Affect Building Orientation and Design

The relative position of the Sun is a major factor in heat gain in buildings, which makes accurate building orientation of the building a fundamental consideration in passive solar construction.

Most importantly, a rectangular house’s ridgeline should run east-west to maximize the length of the southern side, which should also incorporate several windows in its design. For this reason, fewer windows should be located on the northern side of the house, where the summer sun can be intense. A deep roof overhang can shade the few windows in this area, as can different types of shade trees and bushes. Research supports an east-west ridge-line.  Homes re-oriented toward the Sun without any additional solar features save between 10% and 20% and some can save up to 40% on home heating, according to the Bonneville Power Administration and the City of San Jose, California.

Builders should note that these directions are given in reference to the Sun and not magnetic north, which can vary significantly from the Sun’s actual position. Magnetic north, as read from a compass, can still be used as a reference if the builder adjusts the figure based on the location-specific magnetic variation, which can be found in publicly available maps.

Building Tips for New Construction and Building Orientation

The following tips will also assist homeowners and builders in maximizing heat gain through building orientation:

  • Orient the floor plan – not merely the building’s profile – toward the Sun. Design the home so that frequently used rooms, such as the kitchen and living room, are on the southern side. Occupants will appreciate the sunrays in the winter and relief from the sun in the summer. Patios and decks should be built on the south side of the house, where direct sunlight will permit their use for more hours during the day and more days during the year. Likewise, the garage, laundry room and other areas that are less frequently used should be situated at the northern part of the house, where they will act as buffers against cold winter winds.

orientation floor plan Building Orientation for Optimum Energy


  • Beware of mountains. The north/south sun differential is exaggerated in hilly and mountainous regions, where significant climatic differences can be seen over comparatively small areas. A passive solar house should be constructed on the south-facing slope of a mountain to avoid the extreme shading created where the low-angled sun is blocked by the mountain on the north side. Halfway up the slope is ideal, as the mountain’s peak is exposed to strong winds, while cold night-time air flows into the underlying valley, which is also a natural drainage point.slope effect Building Orientation for Optimum Energy
  • Plan for tree shade. Trees are an important factor in passive solar design because they can both provide needed shade on a balmy summer day and starve the house of natural light when it is needed most. Deciduous trees planted on the south side will lose their leaves in the winter and allow natural light to enter the house, while evergreen trees planted on the north side will provide shade from the summer sun. Builders should carefully consider the age, species, growth rate and mature canopy cover of existing trees before deciding where to orient a structure on a building lot. Trees also pose unique danger.
  • Install as many windows as possible, but not too many! The exact number of windows required is different for each house because it’s based on – among other considerations – the local climate.  A “sun-tempered” house should include enough glazing to equal 5% of the conditioned square footage of the house. Remember, though, that windows allow heat transfer more easily than walls, so too many windows can actually drain heat from the house during the cold winter months. Read articles on Window Gas Fills and Window Films to learn how to insulate a house’s glazing.
  • Stray from the rule on east-west building orientation, if needed. The east-west building orientation of the ridge-line may be adjusted to accommodate other factors by up to 20 degrees with only a minimal impact on heat gain.
  • Driveways can get hot! Driveways and parking lots are made using gravel and asphalt – materials that heat up faster and reach higher temperatures than the rest of the yard. Excessive heat there can spill over to the adjacent house, which is why placement of the driveway or parking lot to the south or east of the building can reduce summer heat buildup in southern climates. During the cold winter months in northern climates, a south- or west-oriented driveway will melt snow faster and provide the home with greater warmth.
  • Glass need not be vertical. Custom glass is available that may be tilted to match the angle of the sun and minimize reflection. Angling glass away from the vertical makes it less insulative, however, so builders should balance potential gains in sun exposure with loss of heat to the outdoors.
  • Another environmental factor that should be considered in the equation of building orientation and positioning is prevailing winds, which are the winds that blow predominantly from a single, general direction over a particular point. Data for these winds can be used to design a building that can take advantage of summer breezes for passive cooling, as well as shield against adverse winds that can further chill the interior on an already cold winter day, or even prevent snow from piling up against windows and doors. Detailed information about prevailing winds for specific locations are plotted in a graphic tool called a wind rose, which is usually available from airports, larger libraries, Internet sources, and county agricultural extension offices. As a general rule of thumb, cold winter winds generally come from the north and west, which can be limited by using insulating glazing on these sides of the house. Also, remember that coastal areas typically experience breezes from an onshore direction, while cool breezes flow down valleys from mountain slopes.

Ultimately, factors such as street appeal and the property’s lot dimensions may restrict a builder’s ability for proper building orientation in strict accordance with passive solar techniques. Even while working under these constraints, however, a builder can still create an energy-efficient home through the implementation of energy-saving features, such as low-E windows, adequate insulation, air sealing, and cool roofs.

Building orientation to the path of the Sun will require less energy for heating and cooling the home, resulting in lower energy bills and increased indoor comfort.  Homeowners who are considering new builds should consult a builder to discuss ways to maximize low-cost and no-cost energy strategies with good building orientation .

Window Films

Window Films

Homeowners and business owners can employ a number of methods to “green up” their indoor environments to make the interior more comfortable and to lower heating and cooling costs.  Installing window films is one method.


Window films are represented in three general categories.  Most familiar to consumers is the tinted cellophane-type material that can be applied temporarily or used as needed, as in glare-reducing retractable shades.  Window films can also be semi-permanent, such as window tint that is applied directly to windows and remains in place.  Window films can also be permanent, such as the product Heat Mirror™, which is different from typical window films and tints.  Window films prices range from fairly inexpensive to very expensive.  We can learn more about the different types of window films and the technology available, along with the performance characteristics of window films, which can be useful when it comes time to following an energy audit.

Where Can You Buy Window Films

Window films or tint are available for purchase from hardware stores in long sheet rolls.
window film Window FilmsWindow films are relatively inexpensive and may be applied directly onto windows by the homeowner or business owner to provide shading without blocking all sunlight. This is the same type of tint found on vehicle windows.  Heavy-gauge window films are sometimes applied to windows to keep them from shattering into dangerous shards in case of an impact. Most window films can be cut to fit any size or shape and can be removed with steam or a razor blade and alcohol.

Heat Mirror™ and low-E Window Films

These window films are factory-installed and permanent.  Heat Mirror™ is a clear, three-layer polyester film that transmits light through insulated glass units (IGUs) while reflecting long-wave infrared energy. It was developed by Southwall Technologies in 1980 to reduce the amount of solar heat transferred into a home or commercial building, increasing the occupants’ comfort and reducing energy costs.

Heat Mirror™ can be mounted inside an insulated glass unit in a variety of configurations (one, two or three coated films, uncoated, or low-E coated glass) to provide energy conservation performance ranging from R-6 to R-20 in order to meet the unique requirements of commercial and residential new construction and renovation. Designations include a two-digit number that represents the amount of light transmitted through the coated film.  For example, Heat Mirror™ 22 is designed to block more infrared light than Heat Mirror™ 88.

The polyester film bisects a layer of argon or krypton gas that fills the gap between two glass panes, creating an extra air space that significantly improves the window’s R-value and associated heating and cooling costs. HM1 Final web Window FilmsHomeowners may become confused regarding the properties of Heat Mirror™ and other green products commonly applied to windows, such as low-E coatings, which also use a reflective layer to reflect infrared energy. Low-E film, however, is made from metal or metal oxide instead of polyester and is physically applied to the glass surface.  Unlike Heat Mirror™, a low-E coating does not increase the number of air spaces in an IGU. Debate has persisted for many years concerning which is the better design, with proponents on each side pointing out defects and inefficiencies of the other product. The two designs are sometimes incorporated in the same IGU for additional protection against heat or infrared energy loss.

Amory Lovins is a Colorado resident who pays $0 in energy bills for what may be one of the greenest houses on the planet, according to MSN Money.  Heat Mirror™ and other energy-saving features (many of which are covered in InterNACHI’s robust Inspectopedia article database) have allowed Lovins to harvest 28 banana crops in his indoor banana jungle without the aid of central heating, despite the fact that his Rocky Mountain estate experiences sub-zero blizzards every winter. There are also plans to install Heat Mirror™ in the Empire State Building’s 6,500 windows as part of the building’s energy retrofit project. According to BusinessWire, the installation of Heat Mirror™ in the windows of New York’s tallest building will decrease energy costs by $400,000, cut solar heat gain in half, and improve the windows’ R-values from R-2 to R-8. Skyscrapers and alpine banana jungles aside, most Heat Mirror™ window film is found in ordinary residential and commercial structures, although it is among the more expensive options available.wrinkled Heat Mirror Window Films

Be on the lookout for older types of Heat Mirror™ that are prone to discoloration, warping, becoming brittle, and seal failure. One such defect is yellowing, caused by impurities that make their way onto the film before it is sealed within the glass panes. Wrinkling is also a problem in older Heat Mirror™, as you can see in the accompanying photo. These problems have largely been resolved in recent years, as Southwall has corrected manufacturing errors and more closely scrutinized their licensed distributors.

Heat Mirror™ and other types of window films are designed to reflect solar heat, increase a window’s R-value, and/or provide shading while reducing the building’s energy costs for both heating and cooling, sometimes significantly, depending on the product.  Inspectors who perform energy audits can help with recommendations on the most appropriate choices for the application and budget for window films.


 Window Films


Window Films