Resource

Improving the Thermal Envelope for an Energy Efficient Home

Author: Matt Lee, Bautex Systems

Every home has a thermal envelope. The house cladding, walls, insulation, windows, roof, attic, and basement all come together to keep out the elements and, hopefully, to keep the residents of that house comfortably warm in winter and cool in summer. Some thermal envelopes are much better than others, however. Unless you are Ed Begley, Jr., chances are good that your home’s thermal envelope could use some improvements. The good news is that most thermal envelopes can be improved without spending a fortune.

New homes are not necessarily efficient

There are many companies out there that will conduct an energy audit on your home and pinpoint where, exactly, the house is bleeding energy. This can be particularly valuable for homes that were built up to code in the past ten years or so. Such homes feature quality insulation but installers frequently make mistakes that permit gaps where cold air and summer heat can seep through. Over time, poorly installed insulation also becomes compacted or shredded which also compromises the home’s energy efficiency. Gaps in the insulation of relatively new homes are so common that there are several products on the market specifically designed to correct the problem. Easy to use spray foam and polyurethane is available from several manufacturers.

Small improvements yield big results in older homes

Old houses are, of course, charming. They easily achieve a warmth and historical resonance that is difficult to come by with new construction. However, from a green design perspective, many old houses are a nightmare of energy loss. They simply were not designed with a thermal envelope in mind. An old house that has not been renovated for energy efficiency is typically leaking heat and air from the walls, roof, and even the basement. Many older homes, typically those built before the 20th century, have no real insulation at all, unless they have been remodeled with energy conservation in mind.

With older houses, owners can conduct their own energy audit. All you have to do is wait for a cold day, then put your hand on your window sills. If you feel cold air entering the house, you have a compromised thermal envelope. Feel the bottom of the front and back doors. Is cold air coming through there? Similarly, if your heating bills are exorbitant, that’s another sign of profound energy loss.

Energy efficiency experts mostly argue that, before any other improvements are made on an old house, the thermal envelope must be improved. The measurement of efficiency for newly installed insulation is called an R-value. R is short for “resistance.” The R-value measures the resistance of the insulation material against heat flow. Hence, high R-values mean that the thermal envelope is doing a good job, while low R-values indicate the need for more effective insulation.

The harsher the climate, the more R-resistance a house needs to be effective against the elements and guard against energy loss. In a fairly mild climate, R-values of 13 to 15 will yield good results. However, in regions that have freezing winters and sweltering summers, a higher R-value will be needed.

Energy renovation of old homes doesn’t stop with insulation, however. Window replacement is also a great investment for this-old-house owners. Nineteenth century wood single pane windows are beautiful, but they’re hemorrhaging heat and air conditioning. Double or triple paned glass replacement will stop a great deal of energy loss in its tracks.

Caulking cracks in the outside walls, window sills, and the space between the roof and house is also an easy way to make old homes more efficient and comfortable. Insulating pipes is an easy do-it-yourself project and that guards against frozen pipes.

Achieve net zero with new construction

If you happen to be building a new home, you have unprecedented opportunities to make it so energy efficient, you won’t even feel your utility bills. With a combination of new construction technologies, solar panels, and/or geothermal heat and air conditioning, paying nothing for utilities has become a matter of careful design. Here are some of the features that make a house super green:

Start with green walls and roof—A new energy efficient home begins with keeping out extremes of hot and cold. Walls have always protected us from these elements—up to a point. These days, however, science and engineering have produced super strong wall systems that not only buffer against hot and cold, they also keep out rain and protect the home’s structure against tornadoes and hurricanes. Drive around any neighborhood, the home exterior you are most likely to see is fiber cement or vinyl. Fiber cement siding doesn’t offer much insulation to your wall system, while some brands of vinyl siding have been improved to offer tremendous defense against the elements and savings on energy bills. As siding goes, humble vinyl planks are, so far, the most efficient green cladding for the money.
Consider building your home’s shell with insulated concrete blocks, an energy efficient building product made of engineered expanded polystyrene (EPS), portland cement and recycled cementitious material. This composite building product creates an efficient thermal envelope or wall system with a high R-value.
Go ductless. Traditional HVAC systems waste a deplorable amount of energy in the ducts. Warm air cools as it travels to the room where you want heat. Similarly, cool air heats up as it makes the same trip. New homes that make use of ductless heating and cooling systems will realize tremendous energy savings for their owners.

No excuse for leaky houses

Whether you own an eighteenth century Victorian mansion, are renovating a 21st century home, or building something brand new, there are opportunities to lower your footprint and stop the depletion of the earth’s natural resources. Get started today by getting an energy audit or researching green materials.

References

NREL http://www.nrel.gov/docs/fy00osti/27835.pdf

Envelopes for Hot and Cold http://www.youris.com/Energy/Ecobuildings/Fitting-Hot-And-Cold-Climates-Into-The-Envelope.kl

Going Green Tips http://www.poughkeepsiejournal.com/story/life/2017/01/26/going-green-environment-tips/97056436/

Cladding Systems http://www.yourhome.gov.au/materials/cladding-systems