The technology for enhancing the energy efficiency of historic buildings is improving all the time. Acting now will extend their useful lives and reap benefits for both present and future users.

Historically landmarked buildings and properties in Boulder's historic districts are irreplaceable reminders of the city's past. As energy costs rise and fossil fuel reserves dwindle, improving the energy efficiency of historic buildings is more important than ever.

In 2006, City Council adopted a Climate Action Plan to meet the Kyoto Protocol goals of substantially lower emissions of greenhouse gases. It is the city's aim to create compatibility between historic preservation and energy efficiency goals. One such goal is to make a building's environmental footprint smaller.

Making Your Historic Building Energy Efficient

Most existing buildings, including those in historic districts, can benefit from energy efficiency improvements. Well planned and implemented, these improvements can:

  • Increase comfort in all seasons;
  • Make the building healthier and safer;
  • Save electricity, gas and water;
  • Lower utility bills;
  • Qualify for tax credits; and
  • Enhance the building's value.

These benefits can be achieved while preserving historic authenticity and integrity.

Energy Audits of Historic Buildings

To find out what energy efficient measures make sense for your building, it is recommended you have an instrumented energy audit done by a professional energy auditor, then undertake a combination of do-it-yourself work and work contracted by appropriate building professionals.

A Systematic Approach to a Building's Performance

To analyze options for improving a building's energy performance, an energy auditor views its energy systems and its occupants as interrelated parts of an organic whole. Changes in one part can affect many of the others.

For example, a combination of air sealing, adding attic and wall insulation and adjusting equipment controls can often cure the problems of poor heat distribution and lower bills at the same time. Or if a new furnace or cooling system is really needed, a smaller, more efficient unit along with a tighter "thermal envelope" (the insulated shell of a building) and well-sealed ducts may be the best strategy.

The energy auditor uses a number of instruments to evaluate the function, efficiency and interactions of the energy systems in a building. Watt hour meters monitor refrigerator and freezer performance. Manometers, combustion analyzers and gas leak detectors help in assessing heating, cooling, ventilating and hot water systems for appropriate control settings, efficiency and safety. A calibrated, variable speed fan is temporarily mounted in a doorway and used to measure the relative tightness of the building and identify most sources of leaks. An infrared sensor helps to find insulation voids.

Did You Know?

Except when the wind is blowing particularly hard, the dominant force causing convective losses in homes is called "stack effect." The greater the temperature difference between the inside and outside - and the taller the dwelling - the greater the force of stack effect. The resulting discomfort and energy loss is at a maximum on the coldest day of the year, just when the furnace is working its hardest to maintain comfort. Since infiltration forces are greatest at the bottom of the envelope and exfiltration forces at the top, sealing openings in basements and attic floors is especially important.


The energy auditor usually finds a number of opportunities to save energy without spending much money or time.

Recommendations for lower cost and possible do-it-yourself work items include:

  • Replacing incandescent light bulbs with compact florescent lights(CFLs).
    • New CFLs fit almost anywhere, produce excellent light, are noiseless and outlast candescents tenfold. Over their lifetime, they pay back their initial costs by a factor of 30.
    • The average home in the US has 38 incandescent bulbs. Replacing them with CFLs will save an amount of energy over their 10,000 hour lifetimes equal to that of the gasoline needed to drive a 4 cylinder gas/electric hybrid car around the equator five times.
  • Adjusting thermostats that control hot water heaters, refrigerators, freezers, fans, furnaces, boilers and air conditioners.
    • When appropriate, installing a modern electronic thermostat may be recommended.
    • Setting thermostats back can save lots of energy while ensuring good comfort. Each degree Fahrenheit (F) of continuous set back can produce a 3 percent savings in Boulder's climate. Eight hour only setbacks can save about 1 percent per degree F setback.
  • Modern electronic thermostats can be programmed to suit your schedule and be different on weekdays and weekends. It is easy to override them when needed without changing the program. When a home is air sealed and well insulated, it drifts down in temperature quite slowly even on cold nights - yet may be heated quickly the next morning.
  • Curing water leaks and replacing high-flow shower heads with good-quality, low-flow models
    • Insulate hot water pipes and hot water heater tanks.
  • Air sealing recessed light fixtures that penetrate insulation.
  • Many buildings in Boulder's historic districts have recessed fixtures that penetrate the insulation. Infrared scanning reveals energy losses that melt snow, cause premature roof failure and waste energy. Air sealing and replacing incandescents with CFLs can make it safe to install insulation, thereby addressing all of these problems.

Hiring Building Professionals

Recommendations for higher cost items are usually more complicated and may require the skills of building professionals:

Should old windows be replaced?

  • Although conventional wisdom says yes, energy auditors usually find a number of other energy efficiency measures that are more important and cost effective to deal with first.
  • Sometimes windows need to be replaced; however, window repairs, the addition of an interior pane, appropriate storms, interior blinds, shades and curtains can greatly improve the energy efficiency of historic windows.
  • Installing storm windows (photo on right) can significantly improve the energy efficiency of historic windows while preserving them.

Curing convective and conductive problems

  • Many buildings have high heating bills due to air leaks alone. Historic buildings usually require air sealing a wide variety of leakage areas - including ductwork - and insulating areas that may never have been insulated before. Curing them can not only save a great deal of energy, but also raise comfort and extend the life of the building.

Replacing old boilers or furnaces with modern condensing units by save a lot of energy

  • Condensing units are much more efficient and do not use the main chimney - which may allow for closing this large hole in the envelope.

Replacing inefficient appliances can save a lot of energy, with favorable return on investment

  • Replacing refrigerators with ENERGY STARĀ® rated units can sometimes save over $100 per year.
  • New washers can save both energy and water - how much depends on patterns of use and the characteristics of the old versus new unit.

Front loading clothes washers use half the water and much less electricity than most older machines. Choose an ENERGYSTAR-rated unit. For a list of energy efficient clothes washers and rebate information, visit the Water Conservation Program website.

Review Process & Incentives

Steps to make historically-designated buildings more energy efficient that require exterior changes (including windows and doors) require a Landmark Alteration Certificate (LAC). If you are unsure if your property is designated or want to learn more about the LAC process, please contact the city's historic preservation planning program by calling 303-441-3274.

Interior work does not require a LAC, but extensive rehabilitation work may require a building permit that could energy code requirements depending on the extent of the work. For building permit information visit the Planning & Development Services Online Center or call 303-441-1880. For information on the energy code visit

Energy efficiency upgrades to designated historic properties are eligible for 20 percent State and, in some cases, 20 percent Federal tax credits.

Renewable energy system installations on the exterior of buildings must be reviewed through the LAC process. Rebate information on solar thermal and solar electric systems is available on the Database of State Incentives for Renewables & Efficiency (DSIRE) website.