Nov 13, 2010

Passive Solar Design: Creating Sun-Inspired Homes - Green Homes - MOTHER EARTH NEWS

Equinox HomeInterview by Megan Phelps
Many people who are planning to build a house would like to end up with a green, energy-efficient home, but aren’t sure how to get started. While we may be familiar with the need for insulation, or even with the basics of passive solar design, it’s not always clear how to transform those ideas into an actual house. And just as importantly, how do you build that house without spending a fortune?
Fortunately, architect Debra Rucker Coleman would like to help us answer these questions. Her book, The Sun-Inspired House, outlines her design ideas, while her company, Sun Plans offers a range of house plans, custom design and consulting services for people who want to build beautiful homes that don’t consume a lot of energy.
Here’s what Coleman had to say about her work, the fundamentals of passive solar design, and why it’s always a good idea to design homes (or select house plans) with the sun in mind. As Coleman says, constructing a sun-inspired home begins with a thorough planning process, and choosing or developing a house plan is one of the first steps along that path.

Designing Sun-Inspired Homes

How would you define “sun-inspired” as opposed to “passive solar”?
I like to use the term “sun-inspired” rather than “passive solar,” because with passive solar, you run into confusion with all the different kinds of solar, such as photovoltaics, and now the new Passivhaus standard that’s coming out of Germany.
Also, “sun-inspired” incorporates more than just the heat from the sun — it also incorporates the light from the sun, and the necessity to keep the sun out in the summer.
(Note from MOTHER: We think the terminology gets confusing, too. If you’re trying to pin down what these different terms mean, check out these brief descriptions of the different types of solar and of the Passivehaus standard — which is not the same thing as passive solar design.)
Can you tell us a little about your company?
Sun Plans was established in 2002, and the goal was to be able to offer affordable architectural services throughout the United States, especially related to sun-inspired/passive solar design.
I’d had a lot of questions from people who were asking why there weren’t more passive solar architects or house plans available. So I thought, well, we’ll make them available on the Internet. It started out nationally and now it’s gone international, into Canada.
The other thing was to make it affordable. Typically architects will charge 6 to 15 percent of construction costs, and less than 5 percent of people hire them to design their homes. So we developed an affordable service that’s more along the lines of a house plan company. That keeps the fees — even for a new design — closer to 2 to 3 percent of total construction cost. And that’s only about half of what you’d pay a realtor if you were buying a home.
How much does the actual plan cost?
I’d say the typical cost for buying a plan we’ve developed is about $1,200. If we adapt a plan, those fees really vary, but I’d say on average about $3,000. And to create a completely new custom plan is about $8,000.

Passive Solar in the ’70s and ’80s

Tell me more about your background and how you got interested in passive solar design.
I went to architecture school at the University of Arizona, where the College of Architecture has a five-year accredited architectural degree. That was in the late ’70s, so that was certainly before the current green movement, but also during the first energy crisis.
The instructors were very sensitive to the environment. I think the phrase might have been “environmental design.” You know, they would be asking, “How is your building going to face according to the sun? How are you going to keep the sun out? How are you going to let it in at different times of year? Are you going to work with native materials?”
So that’s where I got the basics of passive solar — even though it wasn’t called that, and it was taught as just one aspect of environmental design. The curriculum also integrated a solid foundation through various engineering classes. Mechanical engineering has to do with the energy a building consumes, so we were constantly aware of heat gain or heat loss through various surfaces.
When did you start actually designing passive solar homes?
It wasn’t until I left Arizona and started working for other firms, that I realized, “Oh my goodness, they’re not even thinking about the way a building should face. They’re not even thinking about where the sun is!” It was what I perceived as the lack of attention to that in other firms that made me decide to go out on my own in 1985, and at that point I established Energetic Design, the company that I had when I lived in North Carolina. I was intent on making all the buildings I designed more energy efficient and to work with the sun as much as possible.
That’s the point in time where I actually took a course called “passive solar design” from a technical college (Guilford Technical Community College), and then found out that North Carolina actually has a fantastic solar center — the North Carolina Solar Center. It didn’t take long to realize that we were a good match and I began assisting with workshops for them.
Also at that time, there was an organization called the Passive Solar Industries Council, which has since evolved into the Sustainable Buildings Industry Council. They developed some guidelines along with the National Renewable Energy Laboratory. It was those guidelines that helped me understand which were the important things to change in a home design in order to make a home passive solar and how to adapt it for different climates. Their simple worksheets included detailed energy data that showed passive solar gain, which is typically ignored in other energy software. It’s disappointing that funding wasn’t continued on developing these guidelines.

What Makes a House Passive Solar

What would you say are the basic elements of a passive solar or sun-inspired design?
Orientation of the home is probably the first.
Window placement within that orientation is next. (Most of your windows should be on the south side of the home if you’re in the northern hemisphere).
Third, the overhang of the south windows and the shading protection of the east-west windows (a lot of times these are porches, or they can be trees).
And then thermal mass (which helps store the sun’s heat) is probably fourth.
How do you add thermal mass to a home?
A lot of people are building with insulated concrete forms and there’s a lot of inherent mass within them. A 4-inch thick concrete slab is also a very economical way of adding thermal mass. Some homes will have 4 inches of brick or stone veneer on interior walls or 8-inch thick free-standing concrete block walls that have both sides exposed and finished with thin stone or tile.
Some people will choose to forgo extra thermal mass because there can be additional costs. So those people may say, OK, I know it’s going to get a little extra hot on sunny winter days, but I’m willing to sacrifice a little comfort, and to go with insulated shades or to crack a window to keep it from overheating. Thermal mass helps some with cooling too, because it reduces the temperature swing of interior temperatures.
What kind of changes to the house plans do you have to make for different climates?
There is surprisingly little difference in the basic house design requirements. However, the details may vary substantially, especially in relation to the amount of insulation needed and the type of south-facing glass. But those details are easily changed without major house plan adaptations.
Most data will say you wouldn’t want to put the exact same home in Minnesota as in Atlanta, but it’s not that different, mainly since they both need to have most windows on the south wall and have an overhang to protect the south windows from summer heat gain.
Warmer climates may need to have the south-facing glass reduced somewhat. For instance, in the United States, I think the very south lower level, which would be Southern California all the way to northern Florida, might need only 5 to 7 percent south glass. You certainly wouldn’t want to go above 7 percent.
And that’s because it would overheat?
Yes, and it would overheat in both summer and winter.
The middle range of climates starting at approximately 34 degrees north (the latitude of Los Angeles, or Columbia, S.C.) and upward are very forgiving with 7 to 10 percent glass.
The extreme northern part of the United States — with the exception of the Pacific Northwest, which as you know is not really that cold — those climates can handle 10 to 12 percent south glass.
But there are very few plans with that percentage of glass because there’s not enough available south wall area. Or you could end up with a long, rectangular home, and that’s not as efficient to heat and cool. The most efficient shape to heat and cool is a cube.
Why is that?
It has the least amount of surfaces to lose and gain heat through for the given volume. But the next most efficient design with passive solar is to stretch the building along the east-west axis to give it a little more south wall area.
One other thing with the extreme southern climates is that they can handle more north glass. We have some plans on the website with north glass, because for example, the client had a really fantastic north view and wanted to take advantage of it.
And the reason you’d want to minimize north glass is because of the heat loss?
Exactly. Because you have heat coming in through the south windows in the winter and the more that you can do to keep that heat in the better. Windows are the weakest link in a home’s thermal “envelope” and so the ones that do not also contribute to the winter heat gain should be minimized.
However, I am not a proponent of putting all your windows on the south and none on the east, west and north because that may result in a home that is uncomfortable in other ways. I think our connection to nature through views to the outside is equally as important as using the sun’s energy. You need to have those windows for the psychological benefit, as well as to provide balanced daylighting and some cross breezes, which are important for cooling.

Serious Energy Savings

Do you have any estimates on how much people reduce their heating costs by choosing a passive solar design?
It really ranges a lot, and it depends on climate. But to answer your question simply, purely on the sun I would say, approximately 20 to 40 percent, with conventional construction. The higher latitudes are going to be at the lower number. However, if you were to take the same building and double the insulation, you’ve probably just doubled the percent of heat gain that the sun is providing.
You know, the heat from the sun is really just one more type of energy. People talk about “zero-energy homes,” but really by heating with the sun you’re just replacing one type of energy with another and reducing the amount of purchased energy required such as gas, electricity or even wood with a more environmentally-friendly alternative.
I would say that for most of the houses we’re designing, energy savings of 30 percent over a code-built home is the minimum that we recommend our clients strive for: 10 percent comes from energy efficiency and a minimum of 20 percent from the sun. Most of our clients are achieving about 50 percent energy savings, and that’s more like 30 to 40 percent from the sun, and 10 to 20 percent better attention to insulation and air sealing.
Some people are going for net zero. But from what I’m reading, 80 percent is a goal that many people are starting to aim for — 80 percent energy savings over a code-built home. With that level of savings, extreme attention to air sealing and additional insulation is required.
Unfortunately, just meeting code really isn’t very energy-efficient since building codes point to minimum requirements. When we prepare Custom Energy Specs, we’ll ask the client, “what are your personal goals” and if they do not know, then we will make recommendations.
Some people will say they want the current Energy Star standard, which is 15 percent better than code, or the new Energy Star 3.0 standard which is 30 percent better than code. And some clients will tell us they intend to get the home Passivhaus-certified, and in that case we’ll specify another, much higher, level of insulation and possibly recommend changes to the type of wall and roof framing, although the design may be able to stay the same.
So this is really the advantage of custom design — you can help people find a plan that fits their particular needs?
Yes, although what I’m finding is that it’s not so much to help them find a plan, because typically people are very particular about what they want in a house plan. They don’t necessarily want the most energy-efficient plan, they want the most energy-efficient plan that fits a particular design.
Also, for most of our homes, the actual drawings may not necessarily need to be modified for increased energy efficiency. When we write Custom Energy Specs, we may list five strategies of reaching R-40 in the walls if the client wants to achieve Passivhaus standards, or five strategies for achieving the Energy Star 3.0 standard. The homeowner and builder can then choose which of the strategies work best based on local costs, available materials and the builder’s familiarity with various construction methods. Then, they can work out the modified construction details with the builder in the field if this is acceptable with the building inspector. Through Adapt-A-SunPlan, those changes can also be made on the drawings if desired.
Do you make recommendations to people on heating systems?
We have a consultant now who works with us, or in some cases works with the clients directly. That’s to help the clients right-size their heating and cooling systems, so they don’t buy a super-high cost system that they may not need for this house because heating loads are so low. Our consultant can work with a subcontractor to help them get the right size system.
Unfortunately, code doesn’t typically accept a woodstove as the code-compliant backup heat source since it has to be maintained and could not work when the homeowners may be away, but we’re talking that level of heating. Sometimes, as inefficient as it might be, the recommendation may be going with electric baseboard heat, because it may be seldom needed, especially in homes with super-high levels of insulation.
Because it’s expensive to run, but you don’t have to run it as often?
Yes, and it meets the code requirements. And yes, if you ran it all the time in a leaky, non-passive solar home it would get expensive, but in this case it’s a very cost-effective option. A small propane unit is another option so long as venting and other safety issues are adequately addressed.

What People Don’t Know About Passive Solar

What are some of the biggest misconceptions you run into with passive solar design?
One is that the house is going to overheat in the summer. But really, what’s more of an issue is the possibility of overheating in the winter. And yes, if the home is not properly oriented within 15 degrees of true south and if there’s not a properly sized overhang on those windows, it can overheat. The Custom Energy Specs that we prepare look at both the proposed orientation of the home and the latitude to verify that the overhang as shown on the plans is an adequate compromise between both the heating and cooling needs for the particular climate. If not, we make a recommendation for the contractor to modify the overhang length in the field. There is not a “one size fits all” solution for overhang lengths for any given climate since it varies based on the south wall height, the window size, window placement on the wall and the roof and overhang construction type.
The second misconception is that people think that it’s going to cost a lot more. But in a lot of ways, there are really no extra costs with passive solar design. You’re taking most of the windows that are typically in a home and you’re putting most of them on the south side. There is a little more cost as you get into the higher amounts of glass due to extra window costs and extra thermal mass needed to store the extra heat.
What else do you want to tell people about designing an energy-efficient, passive solar home?
I would emphasize the importance of a smaller footprint, and a smaller home. One of my biggest frustrations is when people go to our website and say, oh I don’t see a 1,400 square foot plan that has everything I want, so therefore I’ll settle for this 1,800 square foot plan. And then that extra square footage costs — probably as a national average, $120 a square foot, but it varies greatly — and you’re also paying more to heat and cool. It’s worth working with someone, either with us, or, if you’re not comfortable with the web-based design process that we use, working with a local architect or experienced home designer who can help you obtain a right-sized plan.
I’d like to emphasize the hierarchy of thinking about what you want your home to be. Think small and good insulation first, then passive solar. Third, let’s think about a really low-tech simple auxiliary heating system. And then fourth, is to add the active solar, with typically solar hot water being first and photovoltaics last, or other forms of renewable energy that create electricity, such as wind generators.
Also, if people are looking at a two-story home, it’s a good idea to think about reversing that. Instead of your additional floor space being on the second floor, make it a daylit basement. If you have land that slopes to the south, you can build it so that you don’t even know you’re in a basement. And that’s a very energy-efficient space.
What do you like most about passive solar?
I love the fact that we’re taking something from nature that is available on every single site no matter where you live, and we’re incorporating it into our homes to save energy and connect to the environment.
During the ’70s and ’80s, did you ever think that eventually passive solar would be everywhere, that by now almost everyone would be doing it?
Well, yes, I’ve been surprised by how slow the construction industry is to change. More than 20 years ago I published a booklet of passive solar house plans with the slogan “for a green home tomorrow, save energy today,” and the industry is just now “going green.” And still many of the green building programs do not adequately allow for passive solar credits.
I find myself continuously wondering “why would you not integrate something into a new design when it saves you money, costs very little extra, is good for the environment, and makes you comfortable and happy to be home?”
One more question: We’d like to add links to a few of your favorite plans, so people can see examples of passive solar design. What would you say are your 10 favorite plans that you’ve done?
The following Sun Plans are my favorites, primarily because each has one or more of the following features: a small footprint, compact design, ease of construction, a popular floor plan, or creative design.

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