Seattle - Energy Efficiency
In our view, almost no one takes energy efficiency seriously enough, and that is due to low energy prices. The arguments for greater energy efficiency have been made many times before, and more certainly more eloquently than we could ever do. The current energy code is a lot better than nothing, but still results in a house that isn't really all that efficient. Our goal would be to be a zero energy house: one that generates all the energy it uses, but we don't see that as practical for a number of reasons. First, the only power source we have available is the sun, since we know of no wind generator that is appropriate for a city lot (and since the best place for a wind generator is above surface features-typically 60 feet or more, it doesn't seem likely either). Second, there is little useful solar power for 3-4 months a year in Seattle. While some people have called their house "zero energy" by generating extra power in the summer to make up for what they consume in the winter, its takes a lot of PV to do this, and we don't have nearly enough roof surface or budget. (See the zero energy page on what this entails).
Being pragmatic, the goal is just to get as close to zero energy as is reasonably affordable, and that means thick walls and really good windows and doors, as well as a very tight house with mechanical ventilation. For a pretty complete background on energy efficiency see energy in the how-to section.
Since the existing house has a brick exterior, the walls are 9" thick, and since that gives you approximately 50% more space to put insulation we decided on making the entire structure have 9" insulated walls. On the recommendation of the energy consultants (Ecotope) we decided to use Cellulose, which has a slightly higher R-value per inch than BIBs fiberglass, giving us an even greater total wall R-value (note: there are good arguments for both products, for more info see materials i in the tutorial). Since we were already up against the E-W zoning setbacks, and we planned on keeping the existing foundation, making the walls any thicker would have been impractical, although we originally were thinking we'd make them 12" thick. For a 9" thick wall our only real choice for structural material is framing of some sort (wood or steel), with the obvious candidate being a double wall system, since its the most common thick wall framing system. Others have used TGIs (wood I-beams) as framing, or post-and-beam systems, but we knew of no clear advantage of any other system, although we are not familiar with them either. We considered SIPs, but there just wasn't a strong enough argument for them in our view.
Since double wall construction involves a non-load bearing inner wall, a straight wood framed wall would use twice as much wood than a standard 2x4 walls, and even more when compared to "advanced framing" using 2x6s. Our initial idea was to use salvage 2x4s for the non-load bearing wall, but as of this writing we are considering steel studs instead because the framer didn't like the idea of using salvage 2x4s. This would lower our overall R-value a bit, but use less wood. When it comes to overall wood usage, there is an awful lot of wood in subflooring, roof underlayment, exterior sheathing and internal shear panels (since we are in the highest earthquake zone) that reducing wood use in framing isn't likely to make a big dent in overall wood use. We intend to have actual numbers and further analysis in the construction section.
Our existing floor is 2x8s, which when stuffed with cellulose at R3.5/inch gives about an R-25 floor after you've adjusted for thermal bridging, but then added the value of the basement sheetrock, subfloor and finish floor. While this isn't particularly high, the heat loss to the basement is a little less than the attic ceiling since the basement is likely to be 5-10 degrees warmer than outside, has no wind induced convective cooling, and the floor temperature is always a little cooler than the ceiling.
Our original plan had been to insulate the second floor ceiling (which was assumed to be 12" TGIs), but when Bob got greedy and wanted a small office space under a dormer in the attic, it was suggested that we build a SIP roof instead (for more info on SIPs, see construction the how-to section), which at 12" thick would give an R-value of about 48 (about the same as the floor would be), but with somewhat more surface area since the roof covers more area than the corresponding floor below it (and since we decided on a 9/12 pitch roof, its a good amount more). As of this writing there is still a possibility we will frame the ceiling with 12" TGIs instead of the SIP, depending somewhat on price and the complexity of framing the other roof details.
Energy-wise, window manufactures have made little progress in the last ten years: the standard is still double pane, low-E coating and argon fill with a R-value of about three. We wanted much better than this, and in looking over the energy-star website, the only manufactures that built triple pane units regularly and also had insulated frames (the frame is a significant part of the windows heat loss) are all in Canada, where the cold climate forces then to take heat loss seriously (and the government seems to take part in advancing green building). The particular unit we chose is made by Accurate-Dorwin in Winnepeg. We have no previous experience with their products, but they had been using in energy efficient demonstration homes, so we took that as a solid recommendation. The idea is to use triple pane with two low-e coatings on the north, east and west sides and use double pane with a single low-e coating (to get good solar heat gain) on the south.
(Heat loss summary goes here)
Since we are using passive solar only as a backup heat (although hopefully a very significant one), our design criteria are much more lenient than a house intending on using nearly 100% solar (which in our climate is not really an option anyhow). Simply stated, passive solar design is about allowing the sun to enter in the winter, preventing it from entering in the summer and storing the heat of the day to get you through the night. What is all boils down to is having quite a lot of windows on the south side of the house, and overhang over those windows designed to shade them in the summer, very little heat loss, and enough mass in the house to store some heat for nighttime or cloudy days.
In reality it much more difficult than this because the sun is at the same angle in months that are normally quite cold as it is in months that are quite warm, for example the sun is at the same angle on Mar 21 and Sept 21, as well as Aug 21 and Apr 21. The solution is to compromise, allowing a little less sun in the typically cool month of April, and add an adjustable overhang or drop down screen for days in August where it would otherwise be too hot. Since the end of September is usually getting quite cool in Seattle, we chose to design our overhangs so we would get full solar gain from Sept 21 all the way till Mar 21, while on Jun 21 it would shade about half the window. Essentially we opted to risk overheating in the summer in order to not lose any heating in the winter.
To understand why this would be a good tradeoff, you also have to look at the overall window area, which in our design is smaller than is necessary to maximize our solar gain (the rule of thumb is 10-15% of floor area, and although we designed it for about 10% of the floor area of our unit, its only about 8% of the floor area of the two units combined.) With this smaller window area we didn't think that overheating was likely, and although it will likely happen some time, we believe it will be rare, and drop down bamboo screens is a cheap, easy fix. Although we would have liked to use more glass area, doing so would affect such things as the look of the structure, the feel of the rooms and affect privacy, so we opted to compromise on solar gain.
Using a similar argument as to why we could risk overheating, we also felt we didn't need any thermal mass beyond the mass of the house itself (which is not insignificant), because we wouldn't really have extra heat to store, except at times when you wouldn't want it anyhow. In addition, the more mass you add to a house, the longer it takes to change the houses temperature. This means that if you go away and the house gets either too cold or too hot, it could easily take 12-24 hours to get it to a reasonable temperature. Finally, since the house was built on a crawlspace that we indented to turn into a full basement, there was no simple way to incorporate thermal mass.
Judging how our passive solar design works will take at least a year of occupation, and with any luck this site will still be active so we can report on it at that time.
Infiltration & Ventilation
The infiltration of outside air through leaks in the building is often the largest source of heat loss in a building. Through experience, the builder believes we could possibly get as low as .1ACH, or at least .2ACH (natural), which corresponds to about 25-50 CFM of ventilation, but of course that will vary widely with weather conditions. This is somewhat better than the .35ACH that is often given as a good number to aim for. Since this low level of natural ventilation would sometime not be enough fresh air, we also included a mechanical ventilation system via an air-air heat exchanger, which will provide on average, anywhere from 25-150CFM of additional ventilation, depending on how much of the day we keep it running.
While there is at least a market for energy efficient appliances, efficiency hasn't been a top priority for either manufactures or consumers. The biggest energy users are refrigerators (mostly because they're always on) or washer/dryers depending on how much laundry you do, and then dishwashers (but again depending on how much you use it).
When reading the rating for the various appliances consider that the ratings, like the EPA gas mileage ratings are derived from standard tests that may not match your usage. One particular interesting case is the dishwasher test, which was previously done with clean dishes, but had to be changed because dishwasher manufactures starting installing sensors in the dishwasher that adjusted the cycle based on how dirty the water was, so that a senor dishwasher would get a better rating than a non-sensor one, even though with normal dirty dishes the non-sensor might use less energy.
In addition to giving energy use rating, washing machines and dishwashers are starting to have water use ratings on them also.
For other appliances, one of the biggest issues is their "phantom load", which is the amount of power they draw continuously, whether they are on or not. Virtually all TVs, DVD players and other electronic equipment (in fact virtually everything with electronic controls) have some kind of phantom load, which can be anything from just a couple of watts to as much as twenty watts (verify this). While this doesn't add much to your bill, it draws a significant amount of power nationwide over the course of a year. As a simple comparison, every 2watt phantom load uses more energy during the course of the day than running a 1000 watt toaster for 2 minutes. The average house has at least four devices with phantom loads, which at even just 2 watts each, adds up to 192watt-hours a day, which when multiplied by 100 million homes is 19,200 megawatt hours a year, which is the entire output a a typical 500MW generator for straight 38 days!
Compact fluorescent bulbs use a lot less power than incandescent bulbs, but they are still not always the best choice. Fluorescent bulbs contain mercury, and although the amount has been reduced enough to keep them from being classified as toxic waste, they still contain mercury are so there is still some negative environmental consequence of their disposal (how much is of course controversial). Compared to incandescent bulbs, they last much longer, but again the fine print is that turning them on on off reduces their lifetime.
The best way to save energy on lighting is to use good daylighting, and install lighting in the right places and use the right amount of light. Reading and other detail oriented tasks should be accomplished with local task lighting, rather than lighting up the whole room so bright that you can read anywhere.
To find out more see the how-to on lighting.
To read our one year later evaluation on energy click here.