Innovative solutions for creating healthy, efficient, eco-friendly homes

Remodeling for peak efficiency

Many homeowners embark on green renovations without giving energy efficiency the priority it deserves. The energy a home consumes over its life span has a far greater environmental impact than just about any product a homeowner can select. Recycled glass tile and bamboo flooring, for instance, are certainly attractive and can play a role in an overall green strategy. But if you’re really serious about greening your home, you have to pay more attention to less conspicuous, less fun aspects of the design and construction of your renovation: insulation, air-sealing, mechanical-equipment sizing and window selection.

The good news is that these relatively boring improvements have tremendous investment value. That bamboo flooring may look pretty beat up in 20 years, but good insulation will appreciate in value with every increase in energy prices, and in 20 years might well be one of the most attractive features of your house, despite being entirely hidden from view, ironically enough.

The dirty little secret of energy-efficiency improvements, however, is that they frequently don’t achieve anywhere near the results they could or should. The root problem is the difficulty of measuring results. Month-to-month utility bills rarely provide clear-enough feedback for homeowners to be able to say, “Aha! That (fill in your favorite efficiency measure here) is really working.”

Yes, sometimes you can see an immediate reduction in utility costs, such as when you replace an ancient beat-up 60-percent-efficient boiler with a shiny new 90-percent-efficient unit, but far more often the feedback is slow, diffuse and uncertain. As a result, beyond a few really obvious things such as adding insulation to walls that have none, few homeowners and contractors really know what works and what doesn’t. The whole industry is, to a large extent, flying blind, and we’re missing many opportunities we just can’t afford to miss much longer.

Key questions
To achieve significant and reliable results, you and your renovation team need to ask these key questions before, during and after the project:
    • How is the house performing pre-renovation?
    • What are the most effective measures we can make during this renovation to improve the home’s performance?
    • Did we achieve the results we expected? If not, why not?

In my remodeling work, I’ve found that we need a good scorekeeping system to be able to clearly and effectively answer these questions. I like using the HERS index. HERS stands for Home Energy Rating System, and is used most often to determine if a home qualifies for an Energy Star rating.

A certified HERS rater will input a broad range of data about the house into a software program called REM/Rate, and the program will then generate a number. A rating of 100 means the house performs about as well as expected for a house built to current building codes. A rating of 80 or 85 (depending on the climate zone) means you have achieved Energy Star standards, while a rating of 0 means you’re (at least theoretically) at net zero energy. (See sidebar for more information on HERS.)

A rough HERS index range for older homes where I work (metropolitan Boston) is 140 to 190, pre-renovation. With good planning and thoughtful execution, we’re able to get those houses down to a range of 65 to 90 or so, without changing the exterior appearance. When we do add exterior insulation (more on this later), we’re able to get still lower scores.

One of the useful things about a modeling software program such as REM/Rate (many others are available; REM/Rate is the only one used for HERS ratings) is its ability to illustrate “what if” scenarios. Once we input the data for an existing house and its proposed renovation, we can change assumptions to see how the HERS index improves.

We can change the boiler efficiency, the U-factor of the windows (see sidebar), the thickness of the wall insulation, the air leakage rate and many other variables to determine the best package of improvements to get us to our goal. In short, it’s an effective scorekeeping system, and the number it generates is easily understood by the client, the architect and the crew — no advanced engineering required, not even a familiarity with BTUs, therms or kilowatt hours.

The typical cost to get an initial HERS index for your home, model a few what-if scenarios during the planning stage to set a goal and document how close you come to your goal at the end of the project can range from $400 to $1,200. So it’s not inexpensive. But you need to view it as an investment adviser, a home-design tool and a quality-control mechanism all rolled into one.

Scorekeeping strategies
Despite its utility, you do need to keep in mind that a HERS index is an attempt to project a home’s energy performance based on a significant but limited set of data. It works reasonably well with new construction; when applied to home renovations, the correlation between the modeled performance and the actual performance is imperfect at best. Still, it’s a significant improvement over guesswork, and a good antidote to overzealous salespeople and entrenched industry myth regarding the best places to put your energy-improvement dollars.

To help us improve our use of REM/Rate, we also like to track the actual energy performance of the houses on which we work. We collect utility bills representing at least a year’s worth of data prior to construction, and continue to collect data after construction so we can put a real number to the improvements we were able to achieve.

This not only requires a familiarity with therms, kilowatt hours and BTUs, but also means we need to know how to convert one to another. My favorite metric measurement (also imperfect but relatively easy to calculate) is BTUs used per square foot of living space per year (BTU/sf/yr). Here’s a quick summary: Take your total annual kilowatt hours multiplied by 3,414; your total therms of natural gas (if any) used for a year and multiply by 100,000; your gallons of fuel oil multiplied by 139,000; and your gallons of propane multiplied by 91,000.

What you’re doing is taking all your energy usage and converting it to a common unit — BTUs, or British Thermal Units, which is the amount of energy required to raise the temperature of 1 gallon of water by 1 degree Fahrenheit. When you add all those results together, you will know your household’s total energy consumption in BTUs. Divide that by the square footage of living space in your house. If your climate is similar to Boston’s (5,600 degree days), here’s how you rank:
    • 15,000 or below: Outstanding — with a little solar, you might be close to net-zero energy.
    • 15,000 to 30,000: Still outstanding but a bit of a stretch for net zero.
    • 30,000 to 40,000: Some room for improvement but it will be hard.
    • 40,000 to 50,000: Some low-hanging fruit left.
    • 50,000 to 60,000: This is about average for single-family homes; you have some opportunities.
    • Above 60,000: There’s some serious savings opportunities; time to get going.

Tips and advice
So how can you ensure your next renovation or remodeling project results in improved energy efficiency? Here are some tips, advice and thoughts I can pass on, based on what I’ve learned from using these scorekeeping strategies over a range of projects:

If you’re interviewing contractors for an upcoming renovation, ask whether they can document energy improvements they have achieved on past projects. Most contractors — even so-called green contractors — don’t know how much of an impact they have had on a home’s energy performance. One of the reasons for this is that homeowners don’t hold their contractors accountable for energy improvements, so we end up with a supply-and-demand problem: There’s a limited supply of contractors who can document their energy-conscious renovations because most homeowners don’t ask them to.

Just as you need to set a budget for your renovation, consider setting a budget for your energy use, post-renovation. Use the BTU/sf/yr calculations described above to document your current usage, and set a target for how much you want to consume after your renovation is complete. As I discussed, the HERS index is a good planning tool that can help you get close to your goal, but the modeling software doesn’t fully take into account lifestyle choices you make once the project is complete, which can often have a big impact on your actual usage. Set a budget, track your actual usage and continue to make changes and modify behavior until you meet your budget.

With regard to insulation, think outside the box — literally and figuratively. By that, I mean consider adding insulation to the outside of your house instead of just within the walls or roof cavities.

Insulation is most effective when it is continuous and airtight. If you’re just working within the framing cavities — within the plane of the stud walls and roof rafters — you can’t possibly make the insulation continuous or airtight. There’s all that framing lumber in the way, not to mention pipes and wires. But if you add insulation to the outside — in essence, wrap the house in rigid foam insulation — then it’s relatively easy to get continuous and airtight insulation (except, of course, at the windows and doors — you can’t have everything). Exterior rigid foam also reduces the amount of heat conduction, known as thermal bridging, through the framing. Without exterior rigid foam insulation, it will be hard to achieve really deep reductions of energy consumption in most climates. With it, you may be able to see reductions approaching 80 percent or so.

The best time to consider adding some rigid foam insulation is when you’re re-siding your house. And I’m not talking about the one-half-inch-thick stuff some siding contractors add. I’m talking 2 to 6 inches, depending on climate zone.

Obviously, some houses will lend themselves well to this treatment, and some not at all. You will also have to decide whether to replace your windows at that point with new ones. I’m not saying this is an easy strategy, but it is an effective one. And since you will probably only replace your siding every few decades, it’s best to think ahead.

Improving home value
As energy prices increase, concepts of resale value may change. I’ve recently had conversations with clients who, instead of going for the major kitchen and bathroom renovation, have opted for a major insulation retrofit, including significant amounts of exterior rigid foam and window replacements. Their thinking is that extremely low energy bills will be more attractive to prospective homebuyers in 10 or 20 years than a 10- or 20-year-old kitchen and bathroom.

If you’re undergoing or planning a renovation, keep in mind that the easiest time to identify and fix flaws in your insulation is just before the Sheetrock goes up. So negotiate with your contractor to have the work tested with a blower door as soon as the insulation work is complete but before the drywall crew arrives. The blower door will help you identify and seal significant air leaks in the building envelope that will be inaccessible once the wall and ceiling finishes have been installed.

On our projects we like to use the blower door to pressurize the house and use a theatrical fog machine to fill the interior space with fog. We then identify the air leaks by standing outside and looking for places where the fog is escaping from the house. In my energy-auditing work, I’ve seen a lot of bad insulation jobs in newly renovated spaces, and it’s pretty depressing news to deliver to a homeowner. To avoid that depressing news, insist that your project be tested at the right time.

One thing we’ve learned by means of our diagnostic testing with the blower door, fog machine and infrared camera is that it is very difficult to get effective air sealing with fiberglass insulation only. Fiberglass batts, even when well installed, do not really stop airflow the way properly installed rigid foam, spray foam or dense-pack cellulose insulation can.

If you’re using fiberglass batt insulation, it’s extremely important to make sure it is protected on all sides from air infiltration. This is one reason I keep referring to insulation and air sealing rather than just insulation: You can install lots of insulation and still have lots of heat loss from air leaks that the insulation does not necessarily deal with.

Another thing we’ve learned is that using more expensive spray-foam insulation is not a sure thing either. I used to think that spray foam was like magic — that if we used it, we would automatically have a good insulation job. Once we started testing our projects with a blower door, however, we found that it’s actually pretty easy to do a poor spray-foam job. The lesson here (once again): Test your insulation and air-sealing work.

One last thing with regard to insulation: You should take your insulation and air-sealing improvements as far as you plan to before upgrading your heating or cooling equipment. You may find you can buy smaller HVAC equipment (saving some money there) and that it runs more effectively because it’s not oversized (true more for air conditioning than heating). Make sure your HVAC contractor does the right calculations to size the equipment; don’t let him or her just guess. The Department of Energy has calculated that more than 50 percent of the HVAC equipment in homes in the United States is improperly sized.

Deeper reductions
Speaking of HVAC, if you’re using gas or oil to fire your furnace or boiler, keep in mind that sealed-combustion appliances are not only more efficient, they’re safer than atmospheric-combustion appliances. Atmospheric-combustion equipment exhausts up a chimney; sealed combustion typically exhausts out a side wall.

A standard atmospheric-combustion boiler, for instance, may be about 80 percent efficient, while a sealed-combustion boiler should be at least 90 percent efficient. Not only that, the risk of backdrafting carbon monoxide is much smaller with sealed-combustion mechanicals.

As you make deeper and deeper reductions in the energy required for heating and cooling your home, understand that lighting and plug loads loom larger and larger as energy hogs. So don’t focus only on improvements to the building envelope; also think about energy hogs in the house.

Usually the main culprits are unnecessary or obsolete appliances: extra refrigerators in the basement, constantly running dehumidifiers, ancient window-mounted air conditioners. See if you can do without some of these items, and when it comes time to replace them, buy the most efficient appliances you can find.

In addition to old or unnecessary appliances, some lighting strategies also unduly increase a home’s electrical load. Designers love recessed lights, for instance, and for a reason — they can be very attractive and can really enhance a room. But that extra lighting flexibility can come at a real cost. It’s not unusual for just one surface-mounted light to be able to produce the general room illumination of six recessed lights. In our remodeling work, we’re moving away from recessed lights and more toward surface-mounted lights with task lighting. It’s definitely a design challenge, but one we need to face if we are to make significant reductions in energy usage in our homes.

Paul Eldrenkamp is the founder and owner of Byggmeister Inc., a residential design-build remodeling company based in Newton, Mass. He speaks and writes often on energy and environmental issues in residential remodeling. You can reach him at


A remodeling glossary

When remodeling for energy efficiency, you’re likely to encounter a number of terms used by builders, contractors, energy raters, architects and other
building professionals. Here’s a quick primer to help you grasp the basics.

BTU: The British Thermal Unit is the amount of energy required to raise the temperature of 1 gallon of water by 1 degree Fahrenheit. It’s useful when making energy calculations for your home prior to remodeling.

Degree days: A method for determining energy requirements for heating or cooling a home. To determine degree days, take the average high and low temperature for a day and average them. If the number is greater than 65 degrees, subtract 65 from the average temperature to determine the number of cooling degree days (a daily average of 80 degrees minus 65 would equal 15 degree days). If the average temperature is lower than 65, subtract the average temperature from 65 to determine the heating degree days (65 minus an average daily temperature of 40 would equal 25 degree days). By calculating degree days, you can assess typical energy demands.

HERS: The Home Energy Rating System is used most often to determine if a home qualifies for an Energy Star rating. A HERS rating of 100 means the building performs about as well as expected for a house built to current building codes, while a score of 80 to 85 means a home has achieved Energy Star-level efficiency. Older, leaky homes can have HERS ratings of 140 to 190. Note that the HERS scale changed in 2006. Prior to July 2006 it was called a “HERS score” and higher was better; now it’s called a “HERS index” and lower is better, so you may get confused if you’re comparing old HERS ratings with new ones.

REM/Rate: An energy analysis software program used by homebuilders, home designers, energy consultants, home improvement contractors and utilities to rate the energy efficiency of homes and identify cost-effective improvements using what-if scenarios. It’s also used to determine HERS ratings and evaluate homes for energy-efficient mortgages.

R-value: The “R” in R-value stands for resistance. The more resistant a material is to the conduction of heat, the higher the R-value. Resistance is important because when there’s a difference in temperature between two sides of a surface, heat will always move toward the cooler side. Understanding R-values (and their limitations) can help homeowners choose the most cost-effective insulation and decide where and how to install these products.

Therm: A unit of energy equal to 100,000 BTUs.

U-value or U-factor: A measure of how much heat passes through a building component, such as a window or radiant barrier. Another way to think of it is as a measure of heat loss. With U-values, the lower the number, the better (which is the opposite of R-value). Windows with U-values of 0.35 or less are recommended for homes in colder climates, while in warmer climates windows with U-values lower than 0.60 (and often 0.75) can suffice. (In Southern climates, the Solar Heat Gain Coefficient, or SHGC, is more important than U-value. The SHGC is a measure of how well a window blocks heat from the sun, and is expressed as a number between 0 and 1. Again, the lower the SHGC, the better.)