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A Contrarian View of Passive Solar Design

Don’t obsess over south overhangs

Image 1 of 3
You don't need south overhangs. A passive solar house can perform well without any overhangs to shade south-facing windows during the summer.
Image Credit: Peter Powell
You don't need south overhangs. A passive solar house can perform well without any overhangs to shade south-facing windows during the summer.
Image Credit: Peter Powell
Winter shading. Even in winter, when solar heat gain is desirable, this south overhang is beginning to shade the second-floor windows.
Image Credit: Peter Powell
A forced-air radiant slab. Parallel runs of 2-in. metal conduit are embedded in the slab of this passive solar house. The ducts are connected to forced-air plenums.
Image Credit: Peter Powell

By Peter Powell, AIA

I have designed over 60 passive solar homes over the last 35 years and have lived in seven of them. Based on that experience, I have come to a few conclusions which, although contrary to conventional passive wisdom, I have found to be valid. I must qualify these comments by saying that most of my experience has been in the Northeast, primarily in Maryland and Pennsylvania, in areas with 4,000 heating degree days and up. The following comments mostly apply to new construction in similar or colder climates.

Overhangs to shade south-facing windows are ugly, unnecessary, and counterproductive

You don’t need them. The theory is that overhangs should be designed to provide full shading of the south-facing glass in the summer and no shading in the winter. Part of the problem is that most of the standard summer designs for these overhangs are based on June 21 at noon. Unfortunately, this is neither the hottest time of day nor of the summer.

Likewise, winter designs are usually based on achieving no shading on December 21, which is certainly not the coldest day of the winter.

In my experience, these overhangs are not really needed. Because of the high solar altitude in the summer, over half of the solar radiation striking the glass is simply reflected away; another significant fraction of the solar radiation is rejected by the glass coatings.

Most overheating problems in the summer are due to east and west windows — window which can’t easily be shaded and which obviously should be minimized in the design.

The usual reason for overhangs is supposedly to reduce air conditioning costs. I contend this is a red herring, in part because AC is grossly overused in houses. We don’t need to maintain precisely 75°F year around, as some of my clients seem to want. (I even had a client once demand that his house include no operable windows.)

The easy solution to most summer overheating is to open windows. The major cause of summer thermal discomfort is caused not by excess solar gain but by high ambient temperatures and humidity. We shouldn’t throw out the baby with the bathwater by installing overhangs which are counterproductive most of the year and only marginally helpful in August (at least in my climate).

Solar gain in the spring and fall should generally be maximized and the heat stored to minimize any overheating. Overhangs, which by design will be shading as much as half of the glass in these seasons, should be avoided.

Using deciduous trees to shade the south elevation in summer is a major design error

This is a myth that won’t go away. Don’t do it! This theory holds that deciduous trees and vines will shade south-facing windows in the summer and reduce heat gain, while in the winter, when the leaves are down, sun will be able to enter and heat the house. It doesn’t work.

The problem is that the limbs of any tree tall enough to shade the windows in the summer will significantly block the lower winter sun, even with the leaves down. In my area (central Pennsylvania), most of the leaves don’t fall until November anyway, after there have been many cool days and nights when the solar gain would have been useful.

Any new house site should be evaluated with one of the solar path devices to ensure that NO shading will occur within 45° or more east and west of the south elevation, any time of year.

A related problem with tall trees to the south is the likelihood of shading any rooftop thermal or PV collectors in the winter when the sun is low. Such shading can be extremely detrimental to their performance.

A house doesn’t need to be perfectly oriented

I keep reading articles about how to locate true south, using everything from computer programs to measuring shadows through different seasons. Just get a simple compass and correct for declination if you must.

Orienting a house east or west of true south by up to 20° will have no significant effect on solar performance. For example, I currently live in two virtually identical passive solar buildings, a residence and a studio. The studio faces due south and the residence faces 25° west of south. By the end of a sunny day, the overall solar performance of the two buildings is almost identical, with the house performing slightly better in the spring and fall and the studio doing slightly better in the middle of winter.

In general, I favor orienting a passive house at least 10° west of south to improve late-day heat gain while slightly increasing east-facing window area to improve early-day warmup.

It’s possible to have more south-facing glazing than allowed by most rules of thumb

The area of south-facing glazing area can comfortably be 15-20%+ of total floor area as long as there is adequate storage mass and “active” movement of the heat into the storage.

To maximize solar gain while minimizing overheating, immediately move the stratified heat into storage. Don’t rely on natural conduction and convection to move the heat.

Most rules of thumb for south-facing glazed area assume that the storage mass is located only in the south-facing rooms, and they assume direct conduction of the solar heat into that storage. This method is relatively slow and inefficient, except for the limited surface areas which are directly in the sun, and often results in overheating. It fails to take full advantage of the available mass in rooms remote from the sun, as well as the advantages that occur when heated air is moved through hollow masonry walls or hollow floor slabs to remote mass storage.

A house with a larger-than-normal glazed area (which could be 30%+ of the floor area of the south-side rooms) can still be comfortable and productive if solar heat is moved mechanically out of these areas and circulated into other rooms and, most importantly, directly into supplemental storage mass.

I have designed a number of homes using this approach, which involves using a thermostatically controlled fan (usually the furnace blower) set to start when the temperature at the ceiling or ridge of the space rises above a set point of about 75°F.

This same system is also useful to store and distribute excess heat on days when a woodstove is being used. I have used a number of hollow floor systems for this storage including Airfloor, Flexicore precast planks, and most often a double 4 in. concrete slab with 2-in. EMT at 8 in. on center sandwiched between and connected to a supply plenum. (This forced air radiant slab can also be used for air conditioning if necessary.) Pulling stratified air through a hollow 6 in. or 8 in. concrete block wall is also very effective since all rooms exposed to either side of the wall benefit from the radiant heat. This hollow wall storage is also very effective when the site is north facing with no opportunity for significant south glazing. A design with south-facing clerestory windows can work as sort of a hybrid active thermal collector with the heat then mechanically stored in the mass wall.

Peter Powell is an architect in Rays Cove, Pennsylvania.

83 Comments

  1. Dave Brach | | #1

    25% south glass in summer sounds scary to me
    Peter,

    First, I appreciate your insights and experience--everyone should have the benefit of a local architect who knows the climate well. But what is the cooling load for a house with 20%+ south glazing and no shading in Pennsylvania (assuming SHGC>.5)? Sounds a little scary to me. Also, how do you define "total floor area". Gross?, net?, basement included?? And I assume that "glazing area" does not include the area of the window frames?

    I guess I'm wondering: even if one CAN have 25% south glass and store it actively in lots of mass, why would one WANT to? Windows are expensive. Active storage systems also tend to be commplicated and expensive. Not to mention the mean radiant temperature of that window wall on a winter evening with anything but the higest R windows.....

  2. John Brooks | | #2

    Hi Peter
    I like Contrarian viewpoints

  3. Carl Mezoff | | #3

    Overhangs
    Powell's points, "aged in wood," of long experience, are on target, except possibly his argument against overhangs. If you set the overhang adequately above the glazing opening, you do not lose the winter sun. Also, overhangs do other things besides provide shade. They can keep a lot of the heavy weather off the siding, allow you to omit gutters, and can give you a to keep a wood pile dry!

    The 2" EMT storage slab is interesting, but looks like a lot of work and expense. One would wonder if 80F air would be provide enough delta T to get a meaningful amount of heat into the slab.

  4. Doug McEvers | | #4

    Mechanical heat distribution
    If you are using a furnace fan to move stratified heat, insist on an ECM motor, they are available as a replacement through EFI.

  5. Doug McEvers | | #5

    Overhangs 2
    Overhangs help to get rainwater away from the house, energy heel trusses put the overhang high above the top of the window.

  6. Doug McEvers | | #6

    Deciduous trees
    We have 2 large and well pruned silver maple trees on the southwest corner of our house and I would not be without them. Our AC usage in the summer is 250 kWh in Minneapolis for 3,328 sf. This house was built by others in 1978 and has no special energy features other than some fine tuning by me and a 16 SEER, 2 ton AC.

  7. Pete Powell | | #7

    Reply to Dave
    Dave, as you may have gathered, I'm not a big fan of air conditioning- I don't have any AC system in my present home, so the cooling load is a non issue for me. Floor area in my houses is heated area. I seldom design a house with a basement since a slab on grade is ideal heat storage. I'm in a 5900DD location and am happy to collect and store all the heat I can. There really is no downside. The active storage systems I described take a little construction coordination, but once built involve little more than setting the thermostat. I do have roll down insulating shades on the larger picture windows which helps on really cold nites.

  8. Pete Powell | | #8

    Reply to Carl
    Carl, I agree that you design the overhang to eliminate winter shading, but my point is, that if it's designed to provide summer shading, it will undesirably shade part of the glass in the spring and fall.
    I've built 5 houses with this EMT system and it's not all that hard to do nor expensive (as long as conduit prices don't keep going up.) The overall slab thickness is 8" and we are able to keep it at about 70-72 degrees which is quite comfortable and will maintain the house over 65 degrees for over two cloudy days when fully charged.

  9. Pete Powell | | #9

    Reply to Doug
    I agree about the high efficiency motor since it runs all the time when it is sunny or when the woodstove is in use. I'm not a big believer in buiding houses without gutters- I would rather get the water away from the foundation rather than have it dump on the ground. Your trees may well be helping your cooling costs, but my concern still is the possible reduction of winter solar gain.

  10. James Carr AIA LEED | | #10

    Great essay, but...
    Thanks for these great insights. I would only question whether you might be underestimating the heat gain through the building envelope overall, ie the walls and not just the glass. This is made even worse if the ground adjacent to the buildingis heating up, too. We live in a south-facing 1200 SF studio with no A/C in the Boston area. We have a deep overhang on the south and around 40% glazing on S, almost none on E or W. N side is attached. We heat with wood -- 4 cords avg per winter (someone else do the math!). We have large deciduous trees to the S--full shade in summer. Anyway, it works great. Solar gain means the fire dies out on sunny 30 degree days and we don't notice. Summer is comfortable except for the heat-wave days of 85 plus temp with 80 humidity--always cooler than outside. I do believe that the overhang is a key element of the design (which was done by a friend, years before we moved in.)

  11. Pete Powell | | #11

    Reply to James
    James, Your house configuration and climate sound similar to ours, but. our construction is 8" SIPS walls and roof so I don't expect much heat gain through the envelope. On a sunny 0 degree day, we don't need any supplemental heat. (We recently had 2 sunny days with -20 degree wind chill and needed no supplemental heat for 3 days.) I will still argue for 100% solar access for the south elevation in the winter and even without overhangs, we have no overheating from solar gain in the summer.

  12. Doug McEvers | | #12

    AC
    Pete,
    Thank you for considering my rants and making the point of the need for gutters, this should be the code in all climates short of desert conditions. I am all for passive gain and take nearly full advantage in our 1978 rambler. A couple of basic energy saving criteria were met with our home, the attached garage on the NW corner helps to stave off winter winds and the bulk of the glass faces south.
    I do think one should consider though the type of fuel used for both heating and cooling when making a judgement on shading by trees. Virtually all new homes built in the Twin Cities metro have AC, a new home without it would be a hard sell, plus there is the heat island effect.
    Heating here is by natural gas and cooling is by electricity and the CO2 produced by each should be a consideration. I have not crunched those numbers and hopefully someone wiser than I (Martin) could do so given the right information. When I built superinsulated homes in the 1980's, the cooling load was virtually non existent but these homes were in a much smaller urban area where nightly temperatures are less and average wind speeds higher.

    Building design is situational and homes built to code in the Twin Cities at least have a fairly high cooling demand and are not as well insulated in the walls and ceilings as the homes described by Peter.

  13. Rick | | #13

    Nothing Contrarian, Just Some Rediculous or Illogical
    I don't see anything contrarian in your writing. Things like the most undesireable heat gain comes from E-W windows, no trees (even deciduous) on south side, no need for perfect orientation, glazing/thermal mass ratios are all well known by those who have spent any time being interested in the passive solar subject.

    Comments like overhangs are designed for 6/21 and 12/21 which are not the hottest or coldest and so they are not needed is just illogical. The overhangs provide significant shading against high summer sun well before and after 6/21. Your comment about window coatings helping to reflect summer sun is also illogical. Those truly interested in passive solar heating don't want the coatings in the first place. Finally, your comment about just opening the windows instead of AC is just ridiculous--you have fallen victim to writing for the masses while immersed in your own situation. You have 5900 HDD--I don't have to look to see that you are relatively high. You may have gotten away with no AC in houses in Rays Cove, PA and far western MD, but you shouldn't come around here (Chesapeake Bay), where you can almost steam crabs without any added heat or humidity, and propose a house with no AC...hee hee. Yes, humidity is the issue, and its mitigation is extremely challenging without mechanical help.

  14. John Brooks | | #14

    Did you read this part?
    " The following comments mostly apply to new construction in similar or colder climates."

  15. John Brooks | | #15

    Peak Demand Billing...coming SOON
    Gathering,Moving ,storing and distributing heat and "coolth" could be a valuable strategy in Many Climates soon.
    I would like to see more photos and details.

  16. Pete Powell | | #16

    Reply to Rick
    Rick, I designed, built, lived in, and steamed a lot of crabs in the red house shown at the top of the article. It is located on the Chesapeake Bay near Annapolis so I know a bit about humidity too! Although this house has AC, we probably didn't use it more than 3 or 4 days a year. We would circulate cooler nighttime air through the hollow floor and never had any summer overheating from the unshaded glass. Opening windows does work.

  17. Rolf Miller | | #17

    Question on Thermal Mass
    Pete, Very interesting article and great points. I am trying to finish remodeling my home in Colorado Springs. The original portion of the house is basically complete. I stripped the outside walls down and filled them with closed cell spray-in-place foam, then put up 1 inch rigid foam board and covered with drywall. All the interior walls and ceiling have the original wall board of 3/8 inch drywall covered with 5/8 inch of concrete.

    I replaced all the windows with foam filled fiberglass frames and heat mirror glazing packages. I choose the glazing for each window based on orientation.

    I am trying to finish the final phase of the project but am stuck on a few issues, mostly related to thermal mass. This wing is an addition; it has a crawl space, flat roof (zero insulation) and wood floors. I sprayed 5 inches of closed cell foam on the ceiling in between the 10 inch beams, and covered with drywall. I filled the wall cavities with foam and plan to put up the 1 inch foam board next. The whole house is heated with hot water baseboard. I have never needed AC in the summer, so don't expect to need it now. My concern is with winter heating and storage and movement of heat. The room connecting the addition to the main house has an 8 foot sliding glass door with windows on each side with about 8.5 sqft of glass each (u=0.106, shgc=.53). Unfortunately this wall faces approximately west. The main room of the addition is about 24 ft by 15 ft. There is a picture window that faces due south-west (u=0.181, shgc=.63). Not a great orientation for passive solar. The room has a fireplace that was designed by the original owner, who was the chief engineer of NORAD. It has ducting and blowers to circulate air through it and into the room. For a fireplace it is fairly effective at heating the room, probably not efficient or clean burning, but effective. With insulated walls and ceiling, windows that are no longer super leaky single pane alum., the fireplace will quickly overheat the room unless I can circulate the heat to the rest of the house.

    Where can I locate thermal mass, and how much do I need? I thought about using concrete board, but it is only ½ inch thick, is this thick enough to do anything? The thermal time constant is probably too small to actually store anything. Plus I don’t like the idea of putting thermal mass on the exterior walls because it will increase the delta T across the insulated wall. I don’t want to tear up the wood floors for several reasons, including expense and my wife would kill me. There is an interior “L” shaped wall, one side faces the fireplace and the other is in the room with the sliding door. I already removed the ‘70s wood paneling, so could fill the cavities with concrete and cover with concrete board and plaster rather than putting up drywall. Since the sun doesn’t hit this wall directly, will it be effective? I have also read articles that mention using water walls for thermal mass, but have never been able to find anything on how to make them. Is there a way to put a heat exchanger in my fireplace and tie it to my hydronic system to move heat to the other parts of the house? With no attic over this addition, options for putting in duct work to move air to the rest of the house are limited.

    Any suggestions?

  18. User avater GBA Editor
    Martin Holladay | | #18

    My two cents
    Peter,
    Thanks for sharing your years of experience. Like John Brooks, I like contrarian viewpoints.

    I'd like to add a few notes of caution to this discussion, lest impressionable designers make some serious mistakes.

    1. You are designing homes that have a lot of heat gain on sunny days. In very cold weather, the heat gain is desirable. Your furnace fan is a key component of keeping the south-facing rooms comfortable; without your active systems to move heat, these rooms could become unbearable. Few builders are willing to invest in the hollow concrete floors and walls that are an essential component of your system.

    2. Running furnace fans for hours on every sunny day carries a substantial energy penalty. Many furnace fans draw 700 or 800 watts. These fans are expensive to run. They introduce waste heat into the house -- and the heat is generated on sunny days when the last thing you need is 800 watts of expensive additional electric heat. A proper economic analysis of your system must take into account the value of the collected heat -- minus the cost required to move the heat around. Of course, an ECM blower helps -- but still, electricity is required whenever the sun is shining.

    3. I'm guessing that you and I are the same age. Plenty of us veteran builders built passive solar houses in the 1970s that had relatively high south glazing ratios. These houses overheat on sunny afternoons in February, March, and April. How do I know? I built a few. I became a convert to superinsulation and more reasonable south glazing ratios. Too much glass is cold at night, cold on cloudy days, and hot on sunny days. What's to like? Solving the multiple problems of these buildings is relatively easy: just reduce the square footage of south-facing glass.

    4. I like overhangs. Your first photo makes me cringe. I've worked as a home inspector, and I can't tell you how many times I've seen deteriorated siding and rotten window sills on houses without roof overhangs. I'd much rather lose a few hours of sun occasionally and live in a house with good roof overhangs than see my siding deteriorate from weather exposure. Moreover, the aesthetics of a home are important. To me, at least, a house without roof overhangs is an aesthetic line I'm not willing to cross.

    5. You are completely correct about deciduous trees and orienting 20° east or west of south.

    6. Advice to newbies out there: there are a lot of variables involved in the principles that Peter is talking about. For one thing, what type of glazing is being specified? If you are using glazing with a SHGC of 0.30, the performance of all that glass will be dramatically different from the performance of glazing with a SHGC of 0.60. A factor of two difference. Get it right, as Peter evidently has, and you have a house that works. Get it wrong, and you have blown it big time. You end up with a house full of unhappy homeowners, hot in the summer and shivering on winter nights.

  19. John Brooks | | #19

    Aesthetics=overhang?
    Martin,
    All of your warnings should/MUST be considered.
    Aesthetics is a little too personal.
    Tight skinned architecture has been extremely popular in America from Cape Code to the more modern (70's)Architecture of William Turnbull,Charles Moore and Hugh Newell Jacobsen.
    As an Architect I find it attractive.
    As an Architect from Texas I would go with an overhang.

  20. John Brooks | | #20

    Know the Rules, Understand the Rules
    BREAK THE RULES

  21. User avater GBA Editor
    Martin Holladay | | #21

    I agree
    John,
    Of course you're right — de gustibus non est disputandum. My personal architectural aesthetic, honed in part by my years working as a roofer, requires an elegant roof. Ideally, in my mind, the roof sits like a graceful hat, protecting the house from sun, snow, and rain. It should not be cut up into a dozen disparate planes; I like a gable, with two simple slopes. And it needs decent overhangs, including wide rakes. My personal dislikes: shed roofs, complicated roofs with intersecting valleys and dormers, and roofs with stingy overhangs.

    But aesthetics are personal and not subject to argument.

  22. Rick | | #22

    Pete's Humidity Tolerance is Certainly Contrarian
    Pete, I hear your reply comments to mine. Actually, here they are again followed by more of my reply:
    -----------
    Rick, I designed, built, lived in, and steamed a lot of crabs in the red house shown at the top of the article. It is located on the Chesapeake Bay near Annapolis so I know a bit about humidity too! Although this house has AC, we probably didn't use it more than 3 or 4 days a year. We would circulate cooler nighttime air through the hollow floor and never had any summer overheating from the unshaded glass. Opening windows does work.
    --------
    Pete, I grew up in an old house near the Chesapeake Bay with no AC, ever, but we did have well ventilated toilet facilities. I could proclaim that literally sweltering myself to sleep "worked," and of course it does work if it has to, as in the days of old. You may have been comfortable in the red house, but I doubt if 99 out of 100 other people would be. Of course you got some nice cool by being ON the bay, and by floor channels but the humidity would have been considered a disaster by most. Also worth mentioning is Kachedorian, Passive House, and Doubs, all of whom or which had problems or rumored problems with mold associated with earth tubes or underfloor channels involving passive "earth" cooling.

  23. Doug McEvers | | #23

    Overglazing
    Another reason these homes may be getting by without AC is the nightly radiational cooling from all that glass. I would love to see some performance figures expressed in Btu's/sf/hdd. My best effort in the 80's for what I would consider a passive solar house was .9

  24. John Brooks | | #24

    Getting by without AC
    His house does not have 14 (murky)inches of foam under the slab either.
    I am not saying everyone should copy his solution....
    We should question EVERYTHING.

    note:murky is an obscure reference ....I know

  25. Doug McEvers | | #25

    Earth connection
    Peter is utilizing some very vaiable and sustainable concepts such as earth cooling, this might use some refinement to eliminate the mold possibility. How about some concrete filled sono-tubes tying the earth to the living space? Not sure how you turn it on and off but it might work for coolth. My friend Larry Kinney sent me a bit of information a while back on what they called the "snug house", I will see if I can dig it up. It was an experimental shed that was highly earth connected and very energy efficient.

  26. Rick | | #26

    tubes
    Doug
    It seems Eric Doub never says anything around here, but I guess he still has earth tubes at Solar Harvest in Boulder integrated with his HRV or ERV, whichever it is. He told me a while back he had discovered evidence of mold in the tubes and threw some ultraviolet lighting into the mix in an effort to mitigate it. I don't know if or how well it works--like with other things, however, you have to watch out for running into diminishing or negative returns if things aren't as passive as you anticipated.

    Sono-tubes sound rather expensive. Available knowledge seems to indicate that for US latitudes, you typically need to get down to about 20 feet below ground to get temperatures real close to the average air temperature for the year. Maybe you could live in one big one, all buried except for
    a south-facing glass band near the top, like a green intercontinental ballistic missle (GICBM) silo.

  27. Doug McEvers | | #27

    Gadgets
    Rick,
    I am not sure if I could get military clearance for the design you suggest, but it did give me good laugh along with the steamed crabs.

    When I built 6 superinsulated homes in the mid 1980's, the homes were indistinguishable from the neighboring code built homes. This concept was new to me but building was not and I really felt my homes should fit the surroundings and just be a whole lot more energy efficient.

    I know Eric Doub and he has a different take than I do on what constitutes energy efficiency. I think the net zero energy movement could have learned a lot by studying all of the information that came from Canada and the US during the superinsulation movement. Simple is better when it comes to affordability and efficiency for that matter, square is better than long, that sort of thing.

    Martin described the right roofline as an elegant hat and I agree, slightly bigger than the foundation for rainwater control. The same goes for home design, neat and clean, no great appendages knocking the crap out of the surface to volume ratio. All the gadgets in the world will not make up for a home with improper design, start with superinsulation and Passive House concepts and you will not need all of the expensive countermeasures.

  28. Pete Powell | | #28

    Reply to Rolf
    Rolf, I'm not sure I completely understand your floor plan, but the easiest answer to moving the heat out of this room is a fan assisted transfer grill near the ceiling to blow warm air into adjacent rooms. You say you are only getting solar gain from SW and W facing glass and apparentlly havn't experienced summer overheating, what is happening in the winter? Adding a lot of mass may not be useful unless the room is overheating in the winter. I'm wondering how you do in the winter in this climate with only moderate levels of insulation. I would consider a couple of layers of cement board on the interior wall but don't cover them with wood. There is a discussion elsewhere in this site about hydronic coils in the fireplace. I assume that you have some kind of boiler for heat. Tying a fireplace coil (which can easily produce boiling water or steam) into the conventional hot water system has to be designed carefully. make sure you get help from somebody who knows what they're doing. Don't waste your time with water storage!

  29. Pete Powell | | #29

    Reply to Martin Rick, Doug, John
    OK guys, I appreciate all the comments, so now a few from me. First of all, I won't wade into the aesthetics argument- de gustibus etc and sometimes form doesn't follow function when it comes to overhangs. Yeah, I confess I probably overdesigned some glazing in the 70's and 80's, but maybe that was mitigated somewhat by lower quality windows and not insulating things as well as we do now.

    As far as the summer nitetime cooling thread, this is a very effective measure. I am not using earth tubes in the traditional sense, but simply circulating cool air from inside the house and venting it inside the house. My wife in very vulnerable to mold and other indoor air chemicals and to date she's had no problems with this air tube setup in 4 houses we've lived and used it in. Please note that a critical feature of this scheme is the ability to clean the tubes which we do annually via a shop vac and simple PVC cleanouts in each tube. I don't use Airfloor any more because it can't be cleaned. I found that out years ago when one of the kids gerbils got into the airspace in the floor- never saw it again.

    I think the bottom line to this whole discussion about heat gain/ comfort etc boils down to what level of comfort is expected by the client/occupants. If they expect a high degree of temperature and humidity control, then an "extreme" passive house is probably not right for them. If they are willing and able to open and close some windows and maybe insulating shades, can tolerate some moderate temperature swings, don't need air conditioning 4 or 5 months out of the year and want to save a lot on opering costs, then go for it . We used to have a saying that passive solar houses are for active poeple and active solar houses are for passive people. So I still contend that you can be comfortable with my design suggestions by ventilating in the summer and storing in the winter (even on the Chesapeake.)

    I still fail to agree with the comments about overhangs protecting the siding and preventing window frames from rotting etc. Even on a single story house, a reasonable overhang only protects a small part of the siding from rain, and if you add in a little wind in a rainstorm, it will hardly protect any of it. With the quality of windows, siding, finishes and installation systems we now have, in my experience, this is really not an issue in houses that are designed, built and maintained right.

  30. John Brooks | | #30

    Gerbil Motel
    The Gerbils check in and they never check out ;-)

  31. Cousin Ernie | | #31

    ok nuff bs now
    enbody seen fesser rivasawng?

  32. Rolf Miller | | #32

    From Rolf back to Pete
    Pete, thanks for the reply. Yes the floor plan sounds confusing. The addition is basically a rectangle with a triangle attached, one long side of the addition is inline with the main house wall, this joined wall faces north-east. The addition is not as wide as the main house, so a triangular room on the south-west side connects the addition and the house. The diagonal wall faces a little south of west, this is the wall with the sliding door. This wall connects to the south-west side of the addition where the 14’x5’ picture window is.

    I am not sure if I am completely clear on your suggestion of a transfer grill.
    Before I started this project, the main house had no insulation in the walls. The addition had 2” fiberglass in the walls, and nothing in the ceiling, it had horrible windows. So to answer your question about winter, it was always cold. It did warm up noticeably during the day when the sun was coming in the windows. We have been living in the basement since I started this project, and had to take the baseboard heaters off the walls, so I don’t know how the new windows, doors and insulation have changed things. I expect that the family room will over heat when I use the fireplace. Before, I could easily get that room from 64 degrees to 75 or 80, using the fireplace for 2 or 3 hours, in very cold weather. When you say, “moderate levels of insulation”, are you referring to the before or after? Since the walls of the addition are not complete yet, I could put up 2” of rigid foam over the studs instead of the planned 1”.

    Yes I have a boiler for my hydronic heat system.

  33. Carpet | | #33

    Telling it like it is...
    It is good to see someone else that agrees with summer overhangs. Growing up in Minnesota, June was still cool at night. It is not till the end of July was the heat becoming an issue.

  34. Dave Brach | | #34

    data please
    Peter,

    My question was: "what is the heating load on this type of hosue? " Your anwer: "I don't car for AC". I don't care for AC either, but you didn't answer my question. I am also an architect and am looking for valuable data on passive systems that I can replicate on my own projects. Knowing that you can withstand the heat (how much heat?) is not specificallly helpful for other designers. Also, there is one conspicuously absent piece of information: the SHGC of your 20%-30% south glass. A SHGC of .55 is very,very different from a SHGC of .3.

  35. Pete Powell | | #35

    Reply to Dave
    Dave, your question was what is the cooling load and I answered that that there is none since I have no AC system. The windows in my current house were purchased in 2001 and I believe had a SHGC of .35.

  36. Pete Powell | | #36

    Reply to Rolf
    Rolf, I would definately increase the insulation. To move any excess heat from this room, and not having a forced air system, you need to move the air to other rooms either through an open doorway or using a transfer arrangement which is an opening at the ceiling from this room to an adjacent room with a thermostatically controlled fan, You will also need a similar sized opening near the floor for relief air. This should be more than adequate since you have a relatively small glass area.

  37. Riversong | | #37

    Contrarian or just Wrong?
    First, that red house is one of the ugliest things I've ever seen. Aesthetics might be in the eye of the beholder, but there's timeless and universal aesthetic principles that transcend personal myopia.

    Second, you're using active solar systems (thermostats, fans, remote storage) and calling it passive solar. Those houses are NOT passive solar.

    Third, you're completely wrong about overhangs - studies have demonstrated that significant overhangs correlate highly with durability of exterior claddings and finishes.

    Fourth, if you keep moving out of the solar homes you've built, they can't be nearly as wonderful as you claim.

    Fifth, I've been building passive solar and superinsulated homes for 30 years in much colder climates, I teach passive solar design and construction, and I disagree with most of your "contrarian" points.

  38. jlbaerg | | #38

    And then there are the future owners.
    Friends, Great topic.

    One of the first Passive Solar houses (1200 sqft) I built in the 70's in Montana was heated by a half cord of wood/season. Fortunately the same owner still lives there and enjoys the interaction with the weather. New owners often bring old habits, high comfort expectations and window blinds. In my experience, glare will invariably drive homeowners to cover up much of the south glass.

    Fortunately, we have a new generation of glazing options so that we can architecturally respond to other design considerations. The end result should be pleasing to the eye, comfortable and extremely energy efficient. Can we all agree to document and publish annual energy costs whenever we are describing our "successful" projects? Also some mention of location and climate so as to evaluate various design strategies.

    From my experience in the cold, dry north, I would agree with the deciduous tree and orientation points, but have also found a lot of value in overhangs. Fairly good solar control and building protection. Thanks for the discussion. It's brought some of us old timers out into the open.

  39. Eric Doub | | #39

    Earth tubes, and "energy efficiency"
    I would like to hear more from Doug McEvers or anyone else who understands the main theme of his paragraph:

    "I know Eric Doub and he has a different take than I do on what constitutes energy efficiency. I think the net zero energy movement could have learned a lot by studying all of the information that came from Canada and the US during the superinsulation movement. Simple is better when it comes to affordability and efficiency for that matter, square is better than long, that sort of thing."

    I started looking at superinsulation examples in the early 1980s in civil engineering classes. In 2004 when it came time to create a test house of my own, with the goal of having the home annually produce as much energy as it uses, I deployed what I considered at the time to be the least-cost, simplest measures using standard materials and easily understood methods.

    These measures were guided by "Build Tight, Ventilate Right, Reduce Indoor Emissions." The walls are thermally broken twice, and the ceilings and roofs once. Air leakage was brought down to a moderate NACH of 0.09. We indeed followed the two-step process of Reduce Loads, then Provide Renewable Supplies.

    I am not sure what is being referred to as "gadgets," or what is meant by "constitutes energy efficiency." Living in Solar Harvest, with 5,200 HDD, we use a total of 2.2 kWh/sf/year. This usage is similar to the US single family home average (which is indeed an average, i.e., with no reference to home size). So we are not high-achievers when it comes to minimizing our kWh usage. There is no wood burning, and no gas, but there is an outdoor 360-gallon hot tub, and a steam shower.

    What about that relatively unimpressive (high) usage? The PVs produce a little more than 2.2 kWh/sf/year. So by a small margin we are a net producer. The means to get to this end were indeed simple: Sensible climate-sensitive design; off-the-shelf technologies that can be installed by any competent tradespeople; and building science best practices that can be implemented by tradespeople without a huge paradigm shift or extensive retraining.

    All the components of Solar Harvest that got us to zero net energy cost about 8% more than this custom home otherwise would have: PVs, solar thermal, solar storage tank, thermal break with resilient channels, higher cost windows and doors, sunspace for passive gain but with ductwork and Panasonic inline fans that use about 140 Watts to deliver about 35,000 BTU/hr.

    Yes, 8%. At that level we are close to cost neutral -- what we might be paying otherwise to the utility company, we pay in our mortgage.

    The current HERS 0 house we are building for clients is coming in at a little below 5%. The NREL/Habitat house in Denver was at about 8%, and the single mother of two occupant now probably has at least 5,000 extra kWh on her meter. Gadgets? Energy efficiency? I pay most attention to what is widely understandable and depoyable by the industry, and proven performance.

    Oh, by the way: Solar Harvest is by far the most comfortable home I have ever lived in. And the air quality is good.

    The one clear exception to the above Solar Harvest discussion is the earth tubes. We have installed them once, of our own volition, and this was at Solar Harvest. I do not recommend tubes for clients. One later home does have a tube for the fresh air intake, at the request of clients, and this is to capture cleaner air in the forest away from the nearby highway. This HERS -3 home also has a UV light. If we ever do earth tubes again, I would look into the Rehau silver-impregnated tubes. But I feel that with ERV and HRV efficiencies being fairly high, the ca. 5,000 BTU/hr of heated or cooled air we gain from the earth tubes is something we would readily go without.

  40. User avater GBA Editor
    Martin Holladay | | #40

    Thanks for your great post
    Eric,
    Thanks for your great post.

    For those unfamiliar with Eric's ground-breaking house, it includes 8.7 kW of photovoltaic modules. In most area of the country, 8.7 kW of PV costs about $65,000 to install. Right now, there is a 30% tax credit available for PV, and in some areas of the country there are utility rebates or other incentives as well.

    Nevertheless, some of us still wonder whether adding $65,000 to one's mortgage will really reduce utility bills to the point that the investment proves worthwhile. The incentives help, of course -- but still ...

  41. John Brooks | | #41

    Amen...it is about time
    Eric,
    thank you for joining the discussions....please stay a while
    I can not believe so few of the GBA advisors participate in the discussions.
    Sharing knowledge is the BEST thing we can do.

    Joe Lstiburek answered 4 questions and then backed off.
    John Straube only a few comments.
    Many advisors after one year.... not a single word.
    I would love for my local Mentor ...Jim Sargent to chime in some times.

    Martin,
    Chris Miles (Dallas) just completed a net zero home and the reported cost for PV after incentives was less than $30,000

  42. John Brooks | | #42

    Earth Tubes ...maybe not..probably not
    Condensation issues, maintenance issues, Gerbil issues

    What about the attic as an energy storage container?
    Attic Tubes, Garage Tubes, Crawl space tubes.......
    Simple room to room ventilation...flow by design(not accident)..small ecm fans where needed

    More thermal mass inside the thermal control layer

    moveable shading devices?

  43. John Brooks | | #43

    Simple shapes First..of course
    Simple shapes and careful use of glazing ....agreed

  44. User avater GBA Editor
    Martin Holladay | | #44

    Chris Miles' house
    John,
    About Chris Miles' house:
    1. What was the size (in kW) of the PV array?
    2. Does he have 12 months of energy monitoring data?

  45. John Brooks | | #45

    See for yourself
    Martin,
    here is Chris' website
    http://timbercreekzeroenergyhouse.com/videos.html
    there is a video(2) about the pv

    No there is not a 12 month history..yet

    My impression is that the size of the array is a little bit science and a little bit seat of the pants....
    based on other homes he has built.
    This is a Building America Project

  46. User avater GBA Editor
    Martin Holladay | | #46

    The PV array is 9.03 kW
    John,
    At the Chris Miles house, the PV array is rated at 9.03-kW. The cost to install the PV array was probably about $67,700.

    If the builder and homeowner were able to get the system for only $30,000, it means that the rest of us -- taxpayers and utility rate-payers in Texas -- are helping an upper-middle-class family by chipping in $37,000 to subsidize the construction of their new dream home.

  47. John Brooks | | #47

    30 K is not an official number
    Martin,
    When I went to the presentation....
    The PV guy was mentioning numbers around 30 thousand after incentives
    I do not have the details...

  48. Doug McEvers | | #48

    Eric, at least I brought you out of winter hibernation
    The point I was making is your home is not mainstream, nor do I think it is affordable or cost effective. I have a good amount of experience with superinsulated homes and the monitoring of them, and would like to see a good discussion on this site, superinsulation vs net zero energy.

    I did have a discussion with Paul Norton of NREL about the Habitat House and I think they came close to hitting a home run. The ach50 was a bit high but then the work was volunteer, I think it came in around 2 ach50, 1 or less is achievable and would have helped lower the heating load.

  49. Doug McEvers | | #49

    1/2 cord house
    jlbaerg,

    Please tell us more about the 1/2 cord house, sounds groundbreaking for it's time. Interestingly enough, I was discussing over the weekend, before I read you post, the building specs. for a 1,200 sf house with off-peak electric thermal storage and I felt we could heat the house in NW Minnesota with 10,800,000 Btu's annually, about 1/2 cord. This is state of the art efficiency and you achieved it over 30 years ago, welcome to the GBA forum.

  50. Pete Powell | | #50

    Robert, Sorry you don't like
    Robert, Sorry you don't like that house- it won an American Institute or Architects design award. I certainly would not consider a house "not passive" simply because the house air system is pulling return air through a storage mass. Putting "significant" overhangs on a building to supposedly protect the top few feet of siding is a waste of money and potential solar gain. We'll have to agree to disagree.

  51. Rick | | #51

    Passive, Overhangs, Experts and Studies
    There is no black and white passive. There is no "passive" and "not passive" in describing any given house for humans. We have a long way to go, just to emulate a simple tree, in learning how to re-adapt to the environment and how to use the sun-to be passive. There are people banging their heads on trees, trying to understand photosynthesis. Local experts, here, should understand that the best we can hope for is to integrate passive elements the best we can, and it is useless to say something like "[t]hose [Pete's] houses are NOT passive solar." Even Passive House, although they get an A for effort, is only a goal.

    The utility of overhangs as related to optimizing use of the sun is also not really something that is black and white--many variables including specific insolation, orientation, heating/cooling domination, and on and on. However, I know that I want them where I live, with that desire only partially based on Energy Plus simulations using various scenarios and available, historical weather and insolation data.

    Finally, be very suspicious any time you hear or see the words "expert" and "studies." Take, for example, a statement from above in this blog: "...studies have demonstrated that significant overhangs correlate highly with durability of exterior claddings and finishes." I know a stand-up comedian who uses that study result in his nightly routine. His routine goes something like this:

    " I had to get the cladding on my house replaced today--you know, the siding. Wasn't nothing wrong with it anywhere, and I've lived there for 30 years--no leaks and none blew off. I wasn't gonna replace it but the siding man talked me into replacing part of it. He said that where the shingles overhang my siding by a half inch wasn't a significant overhang and it was messing up my siding durabililty. Well, I told him that's where the worst wind and rain has hit for 30 years and that siding don't leak and it doesn't look any different than anywhere else under overhangs or anywhere else. He said doesn't matter......experts and studies say you got a durability issue cause of that tiny shingle overhang. So I told him to replace only the siding that wasn't under no overhang. He did that and I kind of liked it. It knew my durability was good for another 30 years or so. Felt real good until I got in trouble with the community association cause they didn't like my two-tone house--had to end up replacing all the siding."

  52. User avater GBA Editor
    Martin Holladay | | #52

    Not quite sure what your point is
    Rick,
    Okay, you've introduced a straw man — a hypothetical stand-up comedian who was bamboozled into the premature replacement of perfectly decent siding. The folly of the straw man's decision is clear. And the point is...?

    Yes, it's possible to see siding in good condition on a wall without an overhang. However, here in Vermont, on houses I have inspected, it isn't unusual to see exterior pine trim begin to rot in only 5 or 6 years. Ditto for wooden window sills.

    These problems can be addressed many ways: use only clad windows; use plastic exterior trim. But I'll tell you this: wood trim, wood siding, and wood window sills last much longer when walls are well protected by generous roof overhangs. I base this conclusion on years of observation and inspection.

    Or, to put it another way, I'm an expert, and I conducted a study. (That was a joke.)

  53. Rick | | #53

    Got an apology from my siding man
    Yesterday, my siding man came back and apologized---said that durability study did not apply to aluminum siding like mine. Said he was really sorry he got the wrong study. I said well what was the study for that you were talkin about? He kinda mumbled, sheepishly, well that study was for wood siding. I said, a study for wood siding!!??? You needed a study to tell you that wood siding wasn't going to hold up in the weather!!! Man, give me a refund and get the hell out of here.

  54. Doug McEvers | | #54

    Energy Plus
    Rick,
    Have you developed a "user interface" for Energy Plus?

  55. Rick | | #55

    Energy Plus
    Doug,
    Just so we stay on-subject here, E+ is very contrary and I expect many people are pretty passive about it. I am not a software developer but I have developed a headache using the E+ native user interface. It is a text-base interface and not very user friendly. To me, to get to know it, is like taking another computer programming course--need to focus and think right and keep track of what you are telling sim to do. That's in addition to the need to know something about the actual physical elements, processes, you are trying to sim. The worst part (for me) was that native E+ demands you enter things like walls or solar collectors, for example, into the sim in terms of their x,y,z coordinates! So that's where Open Studio comes in handy. NREL Open Studio is a free plugin for Sketchup (amazing esp. for free) so you can draw your geometry that E+ will accept.. Still, you really need to want to use E+ and pay your learning curve dues to use it. I think it is worth it, because I think it can either do everything energy related already, or they're working on it. Should be called Energy R Us. Another thing, though, is that you have to help them develop it, by way of the help desk, cause it's not all polished yet.

    I am not familiar with any of the commercial user interfaces, but this bit of information (about a year old, now) I found interesting. I asked one of the very-capable guys at the E+ help desk how they could have such a powerful sim program, but so hard to use? He said that earlier in E+ evolution, there was clamor and pressure from the commercial private sector to allow them to develop the design interfaces to E+, but it hadn't really happened very good yet.

  56. Doug McEvers | | #56

    E Plus
    I took a look at E Plus a while back and it is way beyond me to make it work, my brother Dave however is a programmer/analyst and can make sense of these things. It sounds like E Plus can do it all, if a user friendly interface comes about.. Sounds like it can handle multiple buildings and zones and probably could work for district heating, that type of thing. I am currently using Energy 10 and even that software takes some practice to make it work.

    My biggest complaint is the easy to use progarms do not provide the breakdown and itemization that I want so I can apportion heat loss to all of the building elements. Most of my energy calcs. I do with a 10 digit calculator.

    I did expound on your sono-tube gig, hope you don't mind.

  57. Rick | | #57

    GICBM Silos
    Best thing since opti-grabs.

  58. John Brooks | | #58

    Unintended Consequences
    Just remember even Opti-grab had unintended consequences!

  59. Rick | | #59

    Such as Inadvertent Launching During Earthquakes
    John, yes, I know, I was only joking around about GICBM silos in the first place. I thought I would even add a little sarcasm in suggesting that their value might be similar to that of opti-grabs. Even so, I think a certain case could be made for the silos. At least one person or couple has already taken to living in such old silos, although I do not know how green, passive, or even energy efficient they are. My own feeling is that most of us are just not comfortable with spending a lot of subterranean time while we're still alive.

  60. John Brooks | | #60

    What would you do?

    John,
    At the Chris Miles house, the PV array is rated at 9.03-kW. The cost to install the PV array was probably about $67,700.

    If the builder and homeowner were able to get the system for only $30,000, it means that the rest of us -- taxpayers and utility rate-payers in Texas -- are helping an upper-middle-class family by chipping in $37,000 to subsidize the construction of their new dream home.

    Martin,
    I talked to the PV installer the final price of the $60,000 system after incentives from power company and tax credit was less than $27,000
    My question for you.....
    If it were your home and the house was already optimized for low energy....
    Would you install PV?
    Would you take advantage of the incentives?
    Or tell the power company and the Gov to use the money some other way?

  61. User avater GBA Editor
    Martin Holladay | | #61

    I don't begrudge people taking advantage of incentives
    John,
    Of course it's only natural that most of us are happy to take advantage of tax breaks and incentives. (Three years ago I got an $800 tax credit on my solar hot water system.)

    My only point — and it's a policy point — is that the cost is the cost. If you're not paying, somebody else is. I'd really like to see better weatherization incentives for air sealing. The payback is so much faster than it is for PV.

  62. Sea Wolf | | #62

    Seattle Votes YES to Overhangs
    Sun? What's that? You'd be a fool not to consider overhangs in the cloudy, rainy Pacific Northwest, which, come to think of it, isn't that much more cloudy and rainy that the Northeast.

  63. CURTIS L BIGGAR,ARCHITECT-NAHD CGB | | #63

    PETER POWELL AIA PASSIVE CONTRARIAN
    LOT OF COMMON SENSE PETER. I HAVE PRACTICED PASSIVE ENERGY DESIGN SINCE THE AIA PASSIVE ENERGY STUDIO IN 1980. I HAVE SEEN ENTHUSIASM COME & GO AS THE PRICE OF OIL UNDULATES. I HAVE A NATURAL GREEN HOME OF THE FUTURE THAT I AM BUILDING THIS SPRING IN APPLETON WI. WITH OVER 50% SPACE HEAT FROM SUNSHINE ON A CONCRETE SLAB WITH IN FLOOR TUBES TO CIRCULATE THE HEAT THRU-OUT. I USE A HIGH VELOCITY AIR HANDLER FOR CIRCULATING WARM AIR INCLUDING FIREPLACE HEAT.I ALSO USE A CUPOLA IN THE CENTER OF THE BUILDING WITH ELECTRIC AWNING WINDOWS. I ALSO USE PADDLE FANS IN BEDROOMS & VERTICAL OSCILLATING FANS IN LIVING AREAS . THIS IS IN MID WISCONSIN AND I HAVE NOT USED MY AIR CONDITIONING FOR TWO YEARS. MY NEW PROJECTS ARE SOLID LOG OR MASONRY BEARING WALLS WITH 2 LAYERS (3.5") RIGID INSULATION & 2" X 12" ROOF FRAMING WITH 2" SPRAYED FOAM & THE BALANCE FILLED WITH INSULATION. I AM IMPRESSED WITH THE ATTENTION GIVEN TO YOUR COLUMN. MAYBE WE CAN GET RID OF ROOF GARBAGE & GET THE PUBLIC T O RESPECT RESIDENTIAL ARCHITECTS AT LAST. VISIT ME @ http://WWW.CURTISLBIGGARARCHITECT.COM TO SEE MY OFFICE STUDIO & THE NATURAL GREEN HOME OF THE FUTURE.

    CURT

  64. Aaron Marcavitch | | #64

    overhangs are a problem out here...
    Great article, still working on the later posts. Nantucket's Historic District Commission doesn't allow overhangs on many houses, so the ability to get sun shading on new buildings is actually not even possible by the local design regs. I also think that they are a bit un-necessary, but perhaps someone else can persuade me. We just use blinds.

  65. Chad_Ludeman | | #65

    Loving this topic
    Great post and comments so far. Thanks for the effort on everyone's part. I just posted this article on the Passive House forums as I am very interested to see what a certified Passive House consultant would think about the points in this post.

    We attempted to build a Passive House in Philly and when our consultants input proper shading into the Passive House formula, it decreased out cooling load by 2/3's. It also slightly increase our heating loads due to slight blocking of desired solar heat gain in the winter as stated in this article.

    As a developer who is currently including exterior shading in all or our homes in Philly (not far from homes mentioned in this article) I'm very interested to determine if we are just wasting money that would be better spent on higher efficiency windows.

    It was also strange that there was little detail about the specific windows being used in these homes without shading. I would expect more concrete recommendations on U values and SHGC's...

    Lastly, the house in the article looks pretty cool to me. Those blindly insulting all things non-traditional or modern are simply close-minded. I won't insult their taste directly, but they're obviously no in touch with the times it they're insulting AIA award winning designs.

  66. brian | | #66

    This is my first look at this
    This is my first look at this site and my first comment,and I've missed many details that seem to be common references now,but I've been avidly interested in energy-saving design for at least 30 years.Reading this sort of discussion after about 15 yearsoff (overseas) I wonder what happened.I feel as if I was in a time warp.Aside from terminology it seems most commentators are earnestly trying to reinvent the wheel.Physics haven't changed since the days when a lot of people were trying a lot of stuff,but their efforts seem to have been lost to history.I would back everything Peter says without reservation,and I suspect it's because he's been around doing it long enough to know what it's like to live the ideas. Does this mean all the stuff discussed here will also be summarily forgotten and rehashed by the next generation of designers and builders?

  67. User avater GBA Editor
    Martin Holladay | | #67

    Brian, I see you're another old-timer
    Brian,
    I hear you. Indeed, many of today's younger builders and designers missed all of the debates of the 1970s and 1980s, including the passive solar versus superinslation debate. So, be patient. It's a good idea to pass our stories and knowledge on to the next generation. Just because our country got stupid and forgetful during the 1990s, doesn't mean that all is lost.

    We just need to share our stories and knowledge.

  68. jake wright | | #68

    VIEWS TO THE WEST
    Does anyone have any creative solutions for new construction with great views to the west.
    My clients have a great view to the west- looking almost directly at the sunset, but we need to minimize the potential solar gain. Any advice would be greatly appreciated. Thanks.

  69. User avater GBA Editor
    Martin Holladay | | #69

    Response to Jake Wright
    Jake,
    My advice:

    1. Provide windows to the west, but keep the window area reasonable. In other words, specify just a few windows, and resist the temptation to make the windows huge.

    2. Specify glazing with a very low SHGC.

  70. Peter Powell | | #70

    Response to Jake
    Jake, Although I don't know your location, but assuming a primarily heating climate, the first thing I would consider is to rotate the house up to 25 degrees to the west, which won't cause a major impact to your passive gain. If this doesn't face the view enough, then open up the west side as Martin suggests, and provide some type of exterior shades or shutters on the west windows for those times when the heat gain is not acceptable. Another possibilty is to design a permanent trellis which would block the heat gain in all but the lowest sun position but could be configured to not block the view.

  71. John Gant | | #71

    Shading - other solutions than overhangs
    Great discussion, I'm learning a lot about practice versus theory. For solar heat and daylight management, dynamic systems are believed by many to be the best answer - exterior window shading such as solar screens and awnings. Activate them when needed, retract them when not needed. Automation systems are available. Shade devices are modelled in COMFEN, hopefully soon in RESFEN. They are required in many Europe building codes, but not in ASHRAE's ... go figure. These are dependable and effective and durable, and can be configured for specific installations. I am from the shade industry, and am working with LBL and other research groups to create unbiased proofs. Many research reports are out there, and even better information is being developed for the architect and building community.

  72. John Gant | | #72

    Response to Jake W
    I understand the challenge for west-facing windows - not only to control solar gain but also address problems like glare (both direct from the sun and indirect from very bright spots in the room/on the wall), hot spots in the room, thermal discomfort of the occupants, and fading of interior furnishings. I recommend exterior shading devices - with no openness factor or open slats, as even a 1% OF can lead to excessive sunlight in the eyes. Tightly woven fabrics with a very low diffuse transmittance (0 - 10%) would be effective.

  73. Jim Guy | | #73

    Contrarian View
    Peter, I helped design and built-lived in a Passive Solar Home (PSH) about 35 years ago. We won a HUD cycle 1 grant. I lived in the home for several years and my experience was that they are pretty forgiving. We had some roof overhang, I don't remember how much, and lots of glass-mass again I apologize for not having the specifics as I write this. What I remember most is how well the home kept us cool during the summer months by taking advantage of the temperature swings we had in the mountains of SW Va. It was usually 65 or so degrees at night. By having the house closed on 95+ degree days it always felt like 72 when you first entered the home. The other thing I remember is going away for about 2 weeks during a particularly cold windy winter. Frequently the the wind chill was -20 over the two weeks. We only had a wood stove for backup so no heat was on during that time. The house didn't get below 40 during that time. It was insulated well for that time but not by today's standards. We had a floor system like the one you advocate but had a wooden plenum on one end and a masonry plenenum on the other end acting as a manifold where the interface to the manifold was masonry flue block (I don't think they're made anymore. The two interfaces were connected by flue pipe. I never did get the fan working to move hot air although I'm not sure there was lots of air over 75 degrees becasue of all the mass and the fact that the sun hit the floor on the south side and the walls on the north side. I had inoperable windows on the N and S sides with vents designed in via Ken Kern I believe. They worked great. On the E and W wall the windows were operable. My point is that you might need some heavy duty engineering to maximize energy efficiency. But you can do well with 80-20 rules in the PSH domain. We're doing something very similar in Western Md (near Cumberland). We're only 700 ft in elevation there and after this summer I'm concerned that It may be too hot in the cabin (851 SF). I asked my guy about the lack of adequate overhang and he was in your camp. I'm not initially putting on gutters as we're hoping to use a landscaping trick to keep water away from the house (we do have some overhang). Once we get moved into the cabin we're going to continue to build. Perhaps there is collaboration potential. Best ever!

  74. Peter Powell | | #74

    Replty to Jim
    Jim, I was one of the reviewers in the HUD cycle 1 grant program and I still have a copy of the final report including your house. I currently live in Bedford County PA not far from you and have a house with no overhangs on the south but with significant glass area and a 10" thick hollow floor slab for storage. We experience no overheating problems in any season and find that in the summer we maintain very comfortable temperatures even on the hottest days. If you insulate adequately and use decent windows you will definately have excess heat to move into storage. Good luck

  75. John Swearingen | | #75

    Sunny California
    Great posts and great article. "Contrarian" is really a description for reality-based ideas, and it's great to see how the thumb prints for the Rules of Thumb can vary regionally. We design in California, with many homes in the very hot Central Valley and in the Sierra Foothills with lovely west-facing views that are difficult to shade.

    Usually, we design for passive cooling, rather than heating, to allow people to live comfortably without the life-support of air conditioning. Many areas are excellent for night-vent cooling. We design straw-bale houses that have a good 2" plaster surface on all the exterior walls, which allows for pretty good heat transfer on a diurnal cycle.

    Often we have cloudy weather during the winter, which makes solar gain problematic. We try to include thermal mass, such that's available on at 3-5 day cycle, to maintain decent indoor temperatures during those periods, and use moderate south glazing to reduce heat loss in winter and excessive gain in summer. This mass works well as a cooling anchor in summer, as well, when nighttime temperatures might stay high.

    We design overhangs to optimize performance during the transition months in Spring and Fall when a slight difference in performance can make the difference between turning on heat or coasting through the day without. We favor facing east a little to avoid hot western sun in summer, but I agree that it makes little difference overall.

    My home studio is in a poorly insulated converted garage, and I can attest to the benefits of shading: a leafy madrone tree has grown over the years, each summer providing more and more shade, primarily of the roof, lowering the afternoon temperature inside by perhaps 20F from a decade ago. We get very little gain in the winter, so that's not an issue.

    The same elements that work well in summer also work for us in winter: readily accessible thermal mass, good insulation, open air circulation throughout the building (mechanical or passive), and moderate glazing. We're just now building a home with AirFloor ducting, and I'm excited to see how that performs. I think the house will ride like a big Buick, gently following the temperature trends happening outdoors....

  76. Mike O'Brien | | #76

    Glare
    Something that hasn't been much discussed--to me, it's hard to incorporate a lot of glazing into a house and not create glare problems. Low-angle direct sun on one side of a room can make it uninhabitable, both from glare and overheating. It's a real challenge to manage room-to-room brightness across a south facade with a lot of glass. It's easier to manage if windows can be located on more than one side of a room. A good thermal envelope makes it possible to keep solar glass within aperture sizes and locations that the design can accomodate.

  77. James Dontje | | #77

    overhang- it depends
    No experience actually building houses, but once I was doing some passive solar demonstrations with Energy 10 software. A simple, one-story rectangular house in Kentucky (a Habitat floor plan) was the base model. What the model showed was that the window awnings tended to cancel out savings by how they performed in the "shoulder season". As I remember the result, in the fall they let in enough light to add to the cooling load and in the spring they kept out enough to add to the heating load. My conclusion was that the appropriateness of overhangs is determined by the interaction of climate and latitude.

    At the same time and in the same place, I witness the clerestory awnings on some townhouses built by an architect with passive solar experience. The awnings were a grill of large angle iron cross pieces rather than a solid shade. My thought was that the architect had seen the same "shoulder" penalty as I had, and was trying to create a more fitting solution.

    My current house here in MN has a west facing patio door (used to be shaded by an outdoor fireplace that was removed before we came, I'm told). The roof overhang (about 2 feet) is a significant help for part of the afternoon (alas, not all afternoon).

  78. Military Clearance Jobs | | #78

    Always nice to hear
    Always nice to hear contrarian ideas like this.

  79. smalld | | #79

    someone is concious
    Thank you. Robert this is not a article about aesthetics. Refreshing may a phase, however, I would suggest realistic and empirical rather the technical might be the operative. I too, have designed with (no sophisticated electronic systems) homes that well north of the 49th have more than proven that by orientation, glazing selection/placement, interior air/heat/cooling convection resulted in houses (up to 4000 square feet) that required no air conditioning (cooling) 90+ and in a great number of cases no supplemental heating during some of the coldest sunniest days of the year -January:February - -20. Tight --yes-but breathing, as Robert R and I have always advocated - with Solar gain even more. Most clients don't understand thermal banking and the payback. Still I win/they win/we win when they are actually aware and willing. The sun is free energy however the creators of solar gain electronic control systems would hate to hear that or imply that their specific gizmo solves ALL of whatever problem(s) you may have in accessing that free energy. Use it and everything else that the environment that allows us to become what we are with consciousness, morality, and empathy for ourselves, our children, future generation, and the planet that KEEPS US ALIVE.

  80. Anonymous | | #80

    "PASSIVE" SOLAR FANS
    CAN ANYONE RECOMMEND AN ENERGY EFFICIENT FAN USED TO CIRCULATE AIR IN A "PASSIVE' SOLAR HOUSE?. tHE HOUSE WAS DESIGNED TO PULL THE AIR FROM THE TOP FLOOR DOWN TO THE BASEMENT. THE ORIGINAL EARLY 80'S VINTAGE FANS ARE TRUE ENERGY HOGS. THANKS

  81. User avater GBA Editor
    Martin Holladay | | #81

    Response to Anonymous
    Anonymous,
    What size fan (that is, how many cfm)?

    By the way, it's better not to type in "all caps" mode. Some people consider it the equivalent of shouting.

  82. Anonymous | | #82

    At this point i am simply
    At this point i am simply looking for the manufacturers of fans that are currently specified for this purpose. I will research the appropriate size/cfm once i can identify the manufacturers. Thanks

  83. User avater GBA Editor
    Martin Holladay | | #83

    Good fans
    If you need a fan rated at 130 cfm or less, it's hard to beat the Panasonic WhisperGreen fans for efficiency.

    Here's more information:
    http://www.panasonic.com/business/building-products/ventilation-systems/products/whisper-green.asp

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