A Home Energy Efficiency Primer

Illustration from the Building Science Corporation website Houses That Work section.

Sorry: this is a long boring ranty informational post. It’s been brewing up for a while, and I finally sat down and finished it.

I’ve been periodically consulting on friends’ houses and dispensing advice on increasing house energy efficiency and durability. This made me realize that I often miss the opportunity to tell people enough at the ‘getting starting’ phase, or that they don’t think about these aspects until they are well on their way, with a site, rough house plan, even a contractor, before giving me a call.

Considering all the news about oil prices heading towards $70 a barrel (and probably getting worse—peak oil and all that—see info from previous posts), I think that energy conservation is more important than ever, and I hope you would all agree.

This piece reflects my broad brush and philosophical thoughts on building energy efficiency. I can expound on this topic ad nauseum—after all, it was part of my job for seven years at Building Science Corporation, and now part of my graduate studies at UW’s Building Engineering Group. Incidentally, the Building Science Corporation website and Builder’s Field Guides are great resources for learning more about this stuff. But I also realize that the longer this piece is, the fewer will read it. I’ll try to keep it down to the vital points: I describe them as “I would be embarrassed to call a house energy efficient if it didn’t address these items.” But feel free to ask me questions if you want to know the excruciating details. I didn’t come up with a catchy number of points (e.g., top 10 or dozen), but I have divided them into the categories of the design stage, building enclosure (shell), and appliances/mechanical systems.

Design

• Design for climate: We can learn from how aboriginal people built, and take a cue from that. People in the desert once dug holes in the ground, in cliffs, or made massive stone buildings. Nowadays, we ship wood from Canada to the desert to build fake stucco houses around a golf course. Perhaps we should realize that living in Vegas is kinda like making a colony on the moon—we need to ship in water and electricity to survive—but just infinitely more tacky. But more importantly, wherever you are, you need to take the climate loads (cooling, heating, wet, dry) into account: it explains the evolution of local “architectural vernacular.”
  
• Design for orientation/site: News flash: we can now predict where the sun is going to be in the sky, season by season. I wince when I see long thin buildings with the long windowed faces oriented east and west: you get the worst cooling loads all year round. Instead, in a heating (northern) climate, the classic “solar tempered” house has south-facing glass with overhangs to prevent summertime overheating. For a nice example, see the McStain Discovery House—a job I was proud to be involved in. Whenever people claim “energy efficiency costs too much,” I throw this example in their faces—how much does it cost, when the building is just ink on paper, to design it in a non-stupid way?
  
• Building size (square footage): I assume all of you have seen the various news reports on how the average square footage per American is ballooning (from an average 1450 sf in 1963 to 2300 sf today, all while average family size was getting smaller). I am personally disgusted with the trend towards McMansions, using house size as a status symbol (as opposed to character and detail), and the useless space that is used once or twice a year. Obviously, the larger the house is, the more energy it takes to condition it. Sarah Susanka’s work (The Not So Big House, etc) has done a great job fighting against this trend.
  
• Building type/layout: In a similar vein, think of how much “exposed skin” a house has, compared to its floor area. Buildings like townhouses, duplexes, and apartments manage to eliminate one or more walls facing the exterior; the heating and cooling load are largely a function of that metric. I’m not saying everybody should live in apartments: I’m just saying that if you decide you need the single family house with a lawn all around it, there is a price involved. Of course, this “surface area fetish” can be taken too far, as shown by the people who build half dome houses to reduce exposed area.

Building shell (enclosure)

• Insulation: Insulation is good; more insulation is better. This is something I can spend days discussing, so I’ll try to distill it. Insulation is measured in R-value; R-13 is baseline to compare to for walls (the pink batt that goes in a typical 2x4 wall); maybe R-30 for roofs. Depending on climate location, I would say at least R-20 walls are respectable, but don’t go nuts to R-50 or anything (unless you’re building in Antarctica, where it’s called for). A fine framed wall includes foam board insulating sheathing (instead of, or on top of the structural OSB/plywood): it is great for both insulation reasons and moisture/condensation control. To use an analogy, a regular frame wall has insulation for 14-1/2 inches, and wood (R-3.5) for 1-1/2 inches. If you were cold, would you cut your blanket into strips with 1-1/2” gaps between them? There are lots of innovative building systems (e.g. SIPS structural foam panels, insulated concrete forms (ICFs), externally insulated buildings, straw bale construction), but I don’t think that any one of them is a guaranteed winner that will take over the world or anything. But they are all moving in the right direction.
  
• Airtightness: Keeping your house warm or cold is all about making the air inside it warm or cold. In order to control the air, you have to contain the air; therefore, greater airtightness (eliminating uncontrolled leakage) reduces energy use. Of course you will ask: how tight is too tight, and what about sick buildings? Well, any problems I have ever seen or heard about are not just about airtightness: they had poor control of interior pollutants (e.g., smoke, mold, chemicals furniture and furnishings, moisture), and the ventilation rate was too low. That is the key: as the silly catchy phrase in our industry goes, “Build tight and ventilate right.” Also, just because a building is leaky by no means implies that it is healthy—for instance, I’ve seen houses where the biggest single leak was to the garage (with carbon monoxide, stored fertilizer and insecticides, and gasoline)—not the place where you want to be drawing your intake ventilation air. An intentional ventilation system draws air from a known location.
  
• Windows: Yes, I know that windows define the personality of a house, connect indoor and outdoor space, and showcase outside views, if any. But if you look at the R-value of a window, a typical one (vinyl double glazed) is about R-2. That’s about a half inch of coffee cup white foam. A good window is in the range of R-3 to R-4. A window is an R-2 hole in your R-13 to R-20 wall: all of my geek friends should understand the analogy of resistors in parallel. So my recommendation: get good windows (low emissivity coated, double or triple glazed, with argon fill gas), and try to design realizing that the back wall of floor-to-ceiling windows does have energy consequences.

Appliances/mechanical

• Mechanical equipment:. I don’t want too get bogged down in efficiencies, ratings, and other engineering trivia of heating/cooling/water heating appliances. But as a quick summary: if you are buying a 55% efficient water heater (EF=0.55), an 80% furnace (AFUE, annual fuel utilization efficiency), or a 10 SEER (seasonal energy efficiency ratio) air conditioner, you should probably be embarrassed if you think you’re building an energy efficient house. Technology that I would be happy to install in my own home is a tankless instantaneous hot water heater (EF=~0.85), a 90% condensing furnace, and a 12 to 13 SEER air conditioner. Be sure to think about loads and usage: a high efficiency air conditioner is a lot more important in Houston than in Ottawa. So in my list above (assuming Boston), cooling demand is low enough that I don’t think getting a super-efficient (over 14 SEER) air conditioner is economically worthwhile.
  
• Efficient home appliances: Once you’ve tacked the loads of heating, cooling, and water heating, you can start to think of the electric loads of the things inside your house (a.k.a. “plug loads.”) The refrigerator is probably most important, being on 24/7/365: see this writeup in Home Energy Magazine. Get an Energy Star rated product. Next would be lighting: the best realistic technology (besides daylighting, which can be tricky) is fluorescent lighting; compact fluorescent bulbs are probably the most common way to incorporate them into a house plan. CFL technology has been continually improving; try giving the current products a fair shake, if you’ve had bad experiences in the past. You need to wait a minute or so for them to come up to full brightness: don’t judge them just after you turn on the switch. Also, an Energy Star horizontal axis (front loading) washing machine saves both water and energy (and also gets more detergent out of your clothes)--strongly recommended.
  
• Enclosure vs. mechanical choices: As a side note on mechanical equipment, I want to emphasize that given a cost choice of improving the building enclosure (shell) or appliances, you should probably choose the former. A furnace or air conditioner can easily be replaced during its 20-30 year lifespan. Also, mechanical equipment is more likely to be replaced with better evolving technology. Increasing the wall insulation or replacing the windows is a difficult and expensive job. Remember that a house has a pretty long lifespan: if you build an energy hog of a house today, it will still probably be around, sucking down natural gas and electricity, in fifty years.

You might ask: but what about renewable resources and other ‘off grid’ technologies, such as solar photovoltaic panels, home windmills, fuel cells, or gas turbine cogeneration? Well, they are great, but I first would make sure that you maximized my above points: those are the more cost effective ‘low lying fruit’, and not stretching the technology at all. I have been frustrated by too many projects that ignored the body of knowledge of energy efficiency, and just threw on some solar panels to get a ‘green’ label. These advanced technologies are best when teamed to small, efficient houses: they are very expensive (per unit of power produced), so the lower you can make your load, the smaller your investment in solar panels, etc.

If you just don’t want to think about the specifics, one option is to buy an Energy Star Home--Energy Star rates houses, as well as appliances. My work at BSC involved getting a lot of houses to this level. It is pretty decent, but I’d consider it just a start, on the scale of things. As with any rating system, it can be gamed so that the improvements are inexpensive but largely ineffective, and measures that require planning might be dismissed. For instance, in a production setting, I doubt anyone would design for site or orientation.

As a final note, it is foolish to improve building energy efficiency without understanding and addressing building durability. Considering how long it has taken me to finally write this, give me… um… another six months or so to put that post together.