Myths and old-wives' tales abound in the fertile ground of building in harmony with the environment. And many of them appeal greatly to the emotions of recently converted and very enthusiastic environmentalists.
     Building a log cabin in the wilderness seems a wonderful way to commune with nature and grow closer to all that is virginal and greenly clean.
     Oops! That pristine log cabin uses between 10 and 12 times as much wood as a traditionally balloon-framed or "stick-built" home.
     Now, granted that wood is a so-called "sustainable resource", it still ain't infinite. There is a myth that wood is a great insulator, so that cabin doesn't need more insulation. Wrongo! Wood is a moderately poor insulator. A thermal picture taken of a traditionally framed home shows every stud in the outside walls with alarming clarity, demonstrating that the wood is a heat conductor.
     Particularly when building, one should become an arch-conservative, even if his or her political leanings tend toward the moderate or liberal.
     More problems with that idyllic cabin in the woods: the tendency is to nestle it in the trees. Emotionally, that appeals to the person wanting seclusion in the woods. However, those self-same trees may well prevent any solar heat gain through the windows of the cabin.
     Of course, one may ignore the problems of vermin and spontaneous combustion and opt for a straw-bale home. Denial is a very human emotion. "But I've stuccoed the exterior and interior. Not to worry!" Right.
     The real problem is simple. It is myopia - not looking at the holistic home on a year-round basis.
     When one succumbs to the lure of using solar energy - particularly passive solar energy - it is quite easy to focus on the south wall of the home to the exclusion of everything else. A few books written by authors who plagiarize other enthusiasts with little regard for science or facts propagate myths with abandon.
     Let's examine a few of the myths that seem to be accepted as facts by the "solar experts" in the field today.
     "One should build the home below ground as much as possible, because the earth temperature is 58° Fahrenheit there, year-round.
    If that silly idea were really true, why in the world do we bury water lines 6 to 8 feet deep? Water doesn't freeze at 58°, does it? The truth of the matter is this: there is a gradient of temperatures below the surface of the earth in summer or in winter. But when the ground is frozen, the temperature is 32° Fahrenheit.
     If you don't believe this to be true, get a simple thermometer and take the time, yourself, to measure the temperature of cold water in your own house in January. Duh! It ain't 58 degrees, right? Even in mid-summer, it scarcely rises above 55°. In fact, in Chicago, the cold water temperature in January is 32.2° - barely above freezing.
     Even with water lines buried 6 feet or more, you may actually (yourself) have heard of someone having a water line freeze up in mid-winter. Even if you haven't, take our word, it really does happen quite regularly. The water pipe must have gotten below freezing, right?
     However, earth-berm or below-the-earth homes often do use less heating energy than one in the same location above ground. Why? Primarily because infiltration is significantly reduced. But also because of the gradient of temperatures mentioned above. A home below ground loses heat through the walls to the surrounding earth. A semi-stasis will result after a period of time with warmer earth close to the walls and eventually reaching the 32 degrees of ground frost at a distance, reducing the heat loss directly from the walls and roof.
     You may not be familiar with the term "infiltration". It should probably more accurately be called "exfiltration" since heat always migrates from the warmer to the cooler - whether it be by convection (the transfer of heat in this instance by the movement of air), conduction (the transfer of heat from object to object or through an object by contact) or radiation (the transfer of heat over a distance with neither the movement of air or by being in contact).
     In nearly every home we instrumented and tested for heat loss, the single largest heat loss was due to infiltration - air leaks in the structure. Of course, not all leaks can be "patched", nor is it necessarily desirable to make the home "airtight".
     Talking about weatherstrip and caulking is a major turnoff to any solar enthusiast. Damn boring stuff, after all. Not only that, it is an arduous and time-consuming task to actually seal up a real home. Nah! "I'd rather talk about a "thermal mass" learnedly and pontificate at length about the benefits of south-facing walls."
     Then we get to the windows. Yeah, let's give lip service to using double or even triple pane windows. But that ain't nearly as important as which side of the building they are on! (We run into this misconception on a daily basis) Typically, this same expert will talk in deep tones about transfer of "infrared energy" as if he or she really know something about the physics.
     The same expert will typically recommend solar collectors on the roof of the home. Why? Well, dummy, it's closer to the sun! Yeah. Closer by ten feet to an object 93 million miles away. Makes sense to you? We'll do the math for you: it is 0.000000002% closer.
     In actuality, a solar collector on a rooftop gets fully 30% less energy than one mounted at ground level. Why? Something called "albedo". Your expert talking about "infrared" little realizes that the primary solar input to a home is from the visible light spectrum. Neither the shorter wavelengths (ultraviolet) nor the longer wavelengths (infrared) penetrate glass worth a darn. Indeed, you already know this from personal experience. If you sit in your car, you can't get sunburned. The UV won't go through the glass.
     So, if you are collecting solar energy, regardless of the methodology, you are, for the most part, collecting the light spectrum your eyes can see. Look out the window right now. The ground, the trees, the neighboring houses that you can see are all reflecting solar energy to your eyes. That ground reflectance is called "albedo". Keep in mind that it adds 30% (approximately) to the light you would see if you lay on your back on the roof looking at the sky.
     The next time you talk to the "south wall" expert advising you about your solar home, remember albedo. The unobstructed north-facing windows of any home will receive about 23% of the solar input through the unobstructed south-facing windows on the same day at the same time.
     The unobstructed east-facing and west-facing windows will receive about 50% of the energy received by the south-facing windows. However, and this is important, the net solar heat gain through the west-facing windows will be more than that through the east-facing windows because it is typically warmer in the afternoon than in the morning, so the heat losses from the home will be less in the afternoon.
     Heat loss through the walls and windows of your home is linear. All that means is that the colder it is, the more the heat loss is. The technical term for this is "Delta T", or differential temperature. Here in the United States, we calculate heat losses in BTU's per square foot of floor, wall, window and ceiling area per degree Fahrenheit difference between the inside temperature and the outside temperature.
     However, your body warms the interior of your home by about 390 BTU's per hour when you are watching TV and as much as 800 BTU's if you are active. That 100 watt light bulb is adding 341.3 BTU's per hour to the home as well. In fact, everything electrical you have running is adding heat to the home.
     As a result, if the temperature is 65° outside, it is assumed by heating and refrigeration engineers that you need no additional heat input whatsoever to keep the interior at a comfortable 70°.
     Although most of the self-promoting "solar experts" tend to shoot from the hip with facile statements about south windows and optimal house orientation, they nearly always have not taken the time to do a simple heat loss calculation on that same proposed home.
     A sure tip-off that you are being scammed is if you hear talk about heat requirements for a such and such square foot home.
     The square footage of a home does not determine the heating requirements of that home! A 3500 square foot home may well require less heat on a year-round basis than a 1000 square foot home. The heat loss is determined by the construction: the R-value of the walls, the floor or crawl space, the ceiling, the size and kind of windows and most importantly, how well the house is sealed against exfiltration. If the home is "stick-built", has the builder added continuous exterior insulation to prevent conduction through the wood or steel studs? Has the fiberglass insulation simply been placed between studs (which will inevitably and eventually result in a sagging at the top) or has it conscientiously been stapled to the top plate?
     Doing an actual heat loss calculation is a time-consuming job. First, you must obtain the Degree Day data for your own city.
     The National Weather Service through the National Center for Atmospheric Research in Boulder, Colorado maintains records of average temperatures for every day of the year for your locale. If you plan to build in a rural area, they also maintain graphical representations of the average temperatures so that you may extrapolate them for your site.
     For example, if the average temperature (day and night) in your area in January is 15° F, that means that you will have 1500 Degree Days in January. (65° - 15° = 50 Degree Days per day x 31 = 1500 DD)
     You must have the Degree Days for your locale to know what the average heat loss of you home will be. One simple example: let's assume that you have 320 feet of glass area (all sides of the home) If you use dual pane windows, the R-Value will be about R-2. However, if you use "Low-E" (Low emissivity) windows, the R-Value will be about R-3. Doesn't sound like a big deal, does it? But that simple difference will add about 1125 Degree Days to the DD size of your home. On a well-insulated 3 bedroom home, that will increase the heat loss of the entire home by 20%! Going from R-19 in your walls to R-24 will cut one quarter of the heat loss through the walls! And R-44 in the attic instead of R-30 will reduce the heat loss through the ceiling by fully one-third.
     We can hear the rabid enthusiasts tuning out already. "Really boring, man, all this talk about BTU's and stuff. Let's get back to the exciting stuff about south walls and thermal mass."
     But a well insulated home with super-insulation will typically require one-third to one-fourth the amount of heat that the usual tract home or "solar engineered" home will. Because the sad fact is that even most "solar-engineered" homes ignore the mundane stuff like insulation and Low-E windows.
     We like to keep a 1500 square foot home with 320 square feet of fenestration below 5500 Degree Days. Thus, in our example of a 1500 DD January, above, a 5500 DD home will need 8,250,000 BTU's from all sources during the entire month. That's an average 266,129 BTU's per day or 11,088 BTU's per hour. You would require 113 gallons of propane (LPG) with an 80% efficient furnace, or 100 gallons with a 90% efficient furnace at sea level. If you live at a higher elevation, add about 4% more fuel for each 1000 feet. (The energy supplied by the fuel is reduced by about 3% for each 1000 feet due to the thinner air)
     Unfortunately, as complicated as all of the foregoing sounded, there are more complications to consider. First, we haven't taken the heat gain due to solar energy through the 320 square feet of windows distributed on all sides of the home. Worse, we haven't accounted for human nature and human laziness, either.
     As far as the windows are concerned, on a clear night in January (or any other month for that matter) everywhere is equivalent to 3565 Degree Days. This is due to a phenomenon called "night sky radiation". If there are no clouds, your windows radiate heat from inside your home to outer space. For heat loss calculations, that outer space temperature is assumed to be -50° F. Imagine keeping your home warm if the temperature outside were to be 50° below zero!
     So, you must insure that all windows are covered at night. Even simple vinyl vertical or horizontal blinds will do the trick to reduce radiative losses. But they must be closed! Using our 320 square feet of windows example, the heat loss per hour through uncovered windows would be 16,533 BTU's per hour on clear nights if Low-E and nearly 25,000 BTU's per hour if not low emissivity windows.
     And this is a case where triple pane windows won't help, since radiative losses will be nearly identical.
     Human nature bites again during the daytime. Because if those self-same window coverings are not opened, there will be no solar heat gain to the home. It takes a conscious effort to remember to open and close those damned curtains!
     Especially the curtains on the north side of the home. After all, solar experts are forever dwelling obsessively on the south side of the home as if it were the only one that counted! That piddling 30% from albedo inputs is a mere trifle - not worth worrying about.
     A typical home in Minneapolis, Minnesota in January will experience about 100,000 BTU heat input through just 150 square feet of windows distributed equally on all four sides of the home (typical tract home fenestration) if the sun is shining. With an outside temperature of 0°, a 5500 DD home only requires about 15,000 BTU's per hour. Means the furnace ain't gonna kick on.
     We recommend double the fenestration provided with typical tract homes. But, and this is important, we do not recommend that the windows be distributed evenly.
     Rather, you should put more windows on the east side of the home because the major heat requirements for the home occur at night and in the morning. We recommend that you cut down the number of windows on the prevailing wind side of the building. Why? Because the best constructed windows still need to open. As a result, there are inevitable heat losses due to infiltration/exfiltration around the tracks of those windows. The windward side of the home will always have the most convective losses.
     We can hear the wounded and indignant screams of the "solar experts" who have never in their lives instrumented a house on a year-round basis to analyze anything as insignificant as actual heat loss. "Why... why... everyone agrees that the south side or the southeast side of the home should have all the windows!" Sputter, sputter, etc...
     Damned if we can convince them that real people live in a home all the year around. That an ethical designer will take summertime into account as well!
     During the late sixties and early seventies at the height of the solar energy craze, we ran the largest solar equipment corporation in the world. One of the dumbest of the technologies of that time was the so-called "passive solar" notion. Not dumb because it didn't work. But dumb because it didn't account for the American lifestyle. It ain't by accident that our country uses more air conditioning than any other in the world. We don't like being hot. Unfortunately, the early passive solar designs were more enthusiastic than competent. We got dozens of calls each week from folks trying to live in the early iterations of passive solar.
     Now understand human nature. They did not tell their friends and neighbors what a disaster they had fomented. Nah! Indeed, we saw television interviews with some of them proclaiming to the heavens the joys of a passive solar home. But they called us to help them out of the dilemma. "It's too damn cold in the morning and too damn hot in the daytime." They really hated our solution of adding fans and pebble beds to store the solar heat, to make it controllable, to make it available when they actually needed it, since "active solar" was in some mysterious way impure!
     The very idea of using any electricity was an anaethema. Kinda like offering meat to a vegetarian.
     Don't get us wrong. Passive solar can be lived with, if you are willing to adapt. Just like living "off-grid" with solar panels is possible if one doesn't need to watch TV and make toast and coffee at the same time. It just requires slight changes in lifestyle - that's all.
     But let's be real with each other. Most Americans damn well ain't gonna give up their comfortable lifestyle just to "protect the environment". Oh, they may donate to the Sierra Club, but that ain't the same as walkin' the walk.
     So, back to the topic. Your home needs to be designed with summer taken into account as well as winter. Means you should distribute windows with a mind to the beautiful view available to you, but trying as much as possible not to overload the south side. Then pay attention to the angle of the winter and summer sun. Put at least two foot eaves on the sides and at least two feet on the fly-rafters of the home. That'll allow winter sun entry, but tend to screen out some of the summer sun.
     And don't forget that the summer sun will shine directly on the north side of your home both in the morning and in the evening. Yeah, we know, you forgot that the sun rises in the northeast and sets in the northwest in summer...