So what are the ballpark costs for engineering a home to be a passive home? Let's say 2,500 square feet.

Constants are easy to accommodate in design, ICFhybrid. As I mentioned, the peak insolation in my part of the world in Dec would put 40k btu/hr through my windows or four times the typical irradiation. That means a whole lot more mass than the house needs on a regular day. For passive solar, as opposed to solar tempering, modest insolation also means a lot of glass that spent 20 of the last 24 hours as a major hole in my insulation.The question then becomes why do it? I must say that you need other reasons where I live. In my case those reasons are the view and Frank Lloyd Wright.

Lbear, Wright did a series of designs from 1936 on that he called Usonian and that he intended to be haute architecture for the masses. Their best feature was amazing use of space in small homes, in no small part because passive solar let the outside in. That economy is still a toss up because, while not-so-big houses get lip service, they don't get a flood of offers on resale. Yet. But Wright's designs were also meant to save money on construction, and I did so with a slab-on-grade and uncoated double-panes (not possible in the north since IRC 2009.) Solar tempering should cost nothing extra and require only a bit of extra attention to heat distribution. Passive solar can be cheaper to build as well as to operate.

Okay, toddm, so are you saying that you threw out cloud cover data in favor of additional glazing due to personal aesthetics?
Up here, at 49N, you have to work hard to get yourself too much insolation in December and January, and for that matter, November and February. We simply started with a a date, say May 15, although I don't remember exactly what we used. Before this date you are accepting all the insolation possible and after this date you are rejecting all the insolation possible by a variety of means. Think of it as the balance point. Before that date, you are trying to stay warm and after that date you are trying to stay cool. It helps to know something about the climate you are building in, but you can get that information from someone even if you are new to the area. After this, it's just applying passive solar principles to get the adjustments.

So what are the ballpark costs for engineering a home to be a passive home? Let's say 2,500 square feet.

The most powerful method is if you have a set of electronic drawings that can be fed into someone's software. Of course, the software needs to recognize key solar features such as overhangs, tops and bottoms of glazing, R-values and, of course, climate data (by month, at a minimum). Then, you can have it do iterative calculations giving answers on a variety of questions. That shouldn't run more than $1,500 - $3,000, in my opinion. On the other hand, if you have some guy sitting there, laboriously plugging in error-filled numbers to a variety of software packages, you are going to pay a lot more, and get a worse product. SO, it's hard to say.

What I am saying is that you can't know too much about your climate if passive solar is risky there for one reason or another.Recognizing those risks is the strongest argument for modeling software. Here are the mistakes I would have made without HEED:

My initial idea of earth coupling my slab by leaving the center uninsulated was a terrible one. Too much mass is as bad as too little.

In fact, I needed a way of heating mass directly, which led to wood fired radiant heat for days when the sun doesn't shine.

I realized that controlling heat loss through my windows at night was key in my climate to making passive solar work.

Insulating drapes with a radiant barrier over uncoated glass works better than low e windows with high solar heat gain, which really isn't high at all.

Because 90 degree days in April are quite possible, as are 40 degree nights in January, automated daylighting shades are a valuable addition to heavier, more labor intensive drapes.

What HEED was telling me that I failed to heed: Thermal mass can control sensible temps in the summer but you won't mistake it for comfort in a high-humidity climate.

Energy designers are relatively rare and more likely to work on schools and office buildings. At a LEED seminar I attended back when, the only person of the hundred or so ;present to bring up residential was me.If sailawayrb does design analysis and his prices are reasonable, he may be the best bet. But if you email him plans, as ICFhybrid suggests, the ship may already have sailed. Distribution and mass are just as important as glass in many if not most parts of the world. I wish it was easier but it is not.

Lbear -

The cost to “engineer” a passive solar home is likely between zero and several hundred dollars depending on your passive solar design objectives. The additional cost to “construct” a passive solar home is likely between zero and several thousand dollars depending on your passive solar design objectives.

If you just take a standard home floor plan and do nothing more than just orient the long axis of the home to face due south, you will benefit from some passive solar heating without any additional expense.

The next step would be to begin increasing the window area of this south wall and decreasing the window areas of the north, east, and west walls. This can often be accomplished without any additional construction expense, but you may want do a passive solar heat gain analysis to ensure that you are not at risk of over-heating your home. DIYers can often accomplish this engineering analysis themselves, but you can hire a company to do this for you for typically a couple hundred dollars or less. At this point you also begin to need a floor plan that will enable the passive solar warmed air to circulate within the home and have living space that is suitable for people/furniture given the increased sun exposure. Many standard home floor plans that have a central great room off the south wall can be made to work well with passive solar with only minor modifications to the construction drawings. You can hire an architect to modify existing floor plans to create passive solar construction drawings anywhere from reasonable prices to exorbitant prices. By exorbitant, we have seen some architects charge upward of 6% of the total building cost to create customized passive solar construction drawings. You can purchase existing passive construction drawings anywhere from reasonable prices to exorbitant prices, but you need to be aware that they may not have been engineered at all relative to passive solar heat for your location so you need to be careful. So the cost of getting your passive solar construction drawings can easily vastly exceed the cost of doing the passive solar heat gain engineering analysis, can get exorbitant, and the design may not appropriate for your location if you are not careful.

At some point as you are increasing the window area of this south wall, you will begin over-heating the home during the daylight hours unless you do something to mitigate this. The most common mitigation approach is to add thermal mass (e.g., concrete slab floors or masonry walls that are perhaps 4 - 6 inches thick) to absorb the excess heat that occurs during the daylight hours and slowly release this heat during the night time hours. Some DIYers can sometimes accomplish this engineering analysis themselves, but you can hire a company to do this for you for typically a couple hundred dollars. At this point your home construction cost may increase slightly to moderately because you may have more overall windows than you would otherwise and you may also want higher quality (i.e., more expensive windows) with higher R-values.

The final step if you want to maximize passive solar heating capability is to integrate it with hydronic radiant floor heating. This allows you be more aggressive in capturing solar heat, efficiently conveying any excess heat to other area of building where it is immediately needed, storing it for when and where it is needed, or rejecting it when it is not needed at all. This approach tends to be more appropriate and economical for larger residences or commercial buildings. However, since this approach involves using electrical pumps to operate the hydronic system, it is not considered a pure “passive” solar heating system.

In addition to the passive solar heat gain analysis, you should also do a terrain obstruction survey. If you are lucky and can see the horizon between due east and due west (i.e., don’t see any trees that can’t be removed or hills/mountains that would block the sun) you can avoid this expense. DIYers can often accomplish this engineering analysis themselves by obtaining and using a Solar Pathfinder, but you may be able to hire a local company to do this for you for typically a couple hundred dollars or less.

I should also mention that you should also do a proper heat loss analysis. This is something you really should do for any building (passive or non-passive solar) before designing the heating system. So I wouldn’t characterize this as an additional expense, but it critical to have an accurate heat loss analysis in order to properly engineer the passive solar heating.

Posted By ICFHybrid on 24 Jan 2013 10:05 AM
...snip...
Up here, at 49N, you have to work hard to get yourself too much insolation in December and January, and for that matter, November and February. We simply started with a a date, say May 15, although I don't remember exactly what we used. Before this date you are accepting all the insolation possible and after this date you are rejecting all the insolation possible by a variety of means. Think of it as the balance point. Before that date, you are trying to stay warm and after that date you are trying to stay cool. It helps to know something about the climate you are building in, but you can get that information from someone even if you are new to the area. After this, it's just applying passive solar principles to get the adjustments.
...snip...

That was exactly my approach for designing overhangs for passive solar tempering. I plotted the average high and low temperatures for each month, and the average of the high and low. I made the arbitrary decision that I wanted solar heat gain when the average outdoor temperature was below 48 F (9 C), and no solar gain above that outdoor temperature, as shown at http://www.residentialenergylaboratory.com/rel_energy_use_natural_gas.html. That resulted in a requirement for solar gain between Oct. 8 and May 3 for my latitude of 38.5 deg. I compromised on an overhang (including gutters) of 24" (2' or 610 mm) to get 45% sunlight coverage on my windows at 11:30 AM on May 3, and 100% coverage on Oct. 8, as computed using the overhang calculator at http://www.susdesign.com/overhang/ (cost $10). (11:30 AM rather than noon since the "south" side is actually south-southeast.)

The overhang design did require changing the roof design from gable to hip on the south side, a no-cost change, and an ideal angle for mounting a solar thermal panel. I am expecting the largest monthly natural gas bill since moving into this house 2 1/2 years ago due to many minus 10 F (-23 C) nights, and it should be about $64 for heat, domestic hot water, and cooking.

If the goal is partial passive solar heating (what some like to call solar tempering), then all the fuss about thermal mass can mostly be minimized. Of course, in our area, the solar insolation is pretty reliable, so design is easier. A full passive solar design to meet most of the heating needs would be more fun, but does require attention to thermal mass, as well as a custom house design that was not an option in my case.

Posted By sailawayrb on 24 Jan 2013 01:33 PM
...snip...
If you just take a standard home floor plan and do nothing more than just orient the long axis of the home to face due south, you will benefit from some passive solar heating without any additional expense.
...snip...

I would rephrase this recommendation to say, "Orient the long axis of the home along the east-west direction, so that there is a lot of wall space facing to the south."

Toddm –

Agreed, controlling heat loss thru the windows at night is critical for all climates where you need significant heating at night. As I am sure you know, window R-value is always far worse than the worst wall R-value. As such, windows are always a major contributor to building heat loss. So given the window area typically used on south wall of a passive solar building, you pretty much always want to use insulated drapes at night.

Earth coupling is a very interesting subject onto itself. We are currently working on some earth coupled thermal mass walls that are fully insulated/isolated from the hydronic heated floor slab. The massive footing for this wall is a couple feet below the floor slab. This is a ground-cantilevered wall (not attached to ceiling) because of seismic requirements.

I don’t think I will be able to convince you that historical climatic irradiance data is really only useful for accessing passive solar heating feasibility and sizing the supplemental heating system, and less useful for actually designing the passive solar heating. I think we will just need to agree to disagree.

However, you did convince me that we need to add a table to our instructions that provides the data that apparently isn’t easily obtainable. We will do this.

Posted By Lee Dodge on 24 Jan 2013 01:52 PM

Posted By sailawayrb on 24 Jan 2013 01:33 PM
...snip...
If you just take a standard home floor plan and do nothing more than just orient the long axis of the home to face due south, you will benefit from some passive solar heating without any additional expense.
...snip...

I would rephrase this recommendation to say, "Orient the long axis of the home along the east-west direction, so that there is a lot of wall space facing to the south."

Yes, that is a clearer description...thanks!

...and I fully agree with your and ICFHybrid's design approach.  It is important to account for climatic TEMPS when designing the roof overhang.  I assume you selected the date this target temp historically occured, determined the associated solar altitude angle for this date, and then worked out the roof overhang geometry.

Posted By sailawayrb on 24 Jan 2013 01:55 PM

...and I fully agree with your and ICFHybrid's design approach.  It is important to account for climatic TEMPS when designing the roof overhang.  I assume you selected the date this target temp historically occured, determined the associated solar altitude angle for this date, and then worked out the roof overhang geometry.

The dates were selected based on the graphs shown at http://www.residentialenergylaboratory.com/rel_energy_use_natural_gas.html that include historical temperature data. The solar altitude angle for these dates are taken care of by the overhang model at http://www.susdesign.com/overhang/. The user enters the window geometry and vertical distance from the overhang, and then enters various amounts of overhang. Of course, due to the thermal inertia of the earth, you have to compromise between optimum overhangs for the spring and fall. A smaller overhang in the spring and larger overhang in the fall would be optimum. I use insulating shades in the fall to help address this issue.

I do just want to briefly interject that it is very difficult to build a completely passive solar home and it is realistically impossible to do except in a few selected areas. That's not what I am talking about. I am talking about how every home, everywhere can benefit from passive solar principles. It is very easy to achieve 15% or 20% energy savings using those principles and voila! you have a passive solar. Going to a 25%, 30% or 40% fraction of solar heating is what gets more difficult in terms of tradeoffs and additional building cost.

Lee Dodge -

Yes, I referenced Chris’s susdesign.com earlier in this post and we are avid fans. We intentionally broke out our roof overhang design math into two separate calculators (Passive Solar Altitude Angle and Passive Solar Roof Overhang Design) to better illustrate the seasonal declination angle affect on altitude angle and the affect of selected altitude angles (dates) on the roof overhang design geometry. Frankly, I am not sure if that really helps or hinders the average DIYer? However, we have been astounded by some of the questions we have received relative to apparent solar motion and we have tried to do our part to “educate” too.

Yes, the optimal solution is smaller overhang in the Spring (or larger fenestration aperture or less absorptive “active” thermal mass) and larger overhang in the Fall (or smaller fenestration aperture or more absorptive “active” thermal mass). Have you automated your shades (and perhaps your window opening/closing too) or are you of the KISS approach?

Posted By ICFHybrid on 24 Jan 2013 04:24 PM
I do just want to briefly interject that it is very difficult to build a completely passive solar home and it is realistically impossible to do except in a few selected areas. That's not what I am talking about. I am talking about how every home, everywhere can benefit from passive solar principles. It is very easy to achieve 15% or 20% energy savings using those principles and voila! you have a passive solar. Going to a 25%, 30% or 40% fraction of solar heating is what gets more difficult in terms of tradeoffs and additional building cost.

Yes, all very true.  One would think that even trac homes would be oriented to take advantage of some passive solar heat gain, but even today that is hardly done.  You can get over 50% using passive solar in some parts of the country relatively painlessly.  However, once you start pushing that boundary, you really need to know what you are getting into and what you are doing or you may not be very happy with what you create. 

My frustration with a lot of the passive solar advice still being propagated is that actual clear sky heat gain is hardly ever mentioned as a design criteria.  Many experts still spec X% fenestration area per floor area, Z% thermal mass when over Y% fenestration area, and maybe quesstimate a roof overhang design (although often this is just a constant for all the construction drawings they sell and often doesn't account for gutters).  Anyone who has traveled knows that there is a significant clear sky irradiance difference based on latitude.

Posted By sailawayrb on 24 Jan 2013 04:29 PM
Lee Dodge -

...snip...

 Have you automated your shades (and perhaps your window opening/closing too) or are you of the KISS approach?

My shades and windows are not automated.  Having them automated would be fun, but the cost is relatively high, and I keep track of, and limit, the cost of the changes that I have made to a standard production house to one that will meet net-zero source energy, as shown here.  The payback period for the insulated cellular shades was already quite long (35 years) without adding automation.  I do not expect the shades to last as long as the payback period, but the shades offer a significant increase in comfort, help avoid the need for air conditioning, and provide privacy, and these three factors justify their cost. 

Posted By ICFHybrid on 24 Jan 2013 04:24 PM
I do just want to briefly interject that it is very difficult to build a completely passive solar home and it is realistically impossible to do except in a few selected areas. That's not what I am talking about. I am talking about how every home, everywhere can benefit from passive solar principles. It is very easy to achieve 15% or 20% energy savings using those principles and voila! you have a passive solar. Going to a 25%, 30% or 40% fraction of solar heating is what gets more difficult in terms of tradeoffs and additional building cost.

Yes, I think my passive solar contributes about 30% of the energy required to heat the house over the heating season, but I live in a high solar insolation area and have a well-insulated house, so that is relatively easy.

I can get you started faster. UCLA's Climate Consultant 5 will tell you how many hours per year an energy strategy will provide comfort based on weather data from the nearest NWS station. If passive solar/high mass is a runaway No. 1, you are golden. If it is a distant third, as in my case, some digging is in order.

This approach assumes that energy efficiency is secondary to what you want in a home. And on that front, I have a final caution on passive solar. Put the bird houses too close to the windows and you're going to hear multiple THONKS per hour.

Sheesh. That is some software package.

Posted By Lee Dodge on 24 Jan 2013 05:18 PM

Posted By sailawayrb on 24 Jan 2013 04:29 PM
Lee Dodge -

...snip...

 Have you automated your shades (and perhaps your window opening/closing too) or are you of the KISS approach?

My shades and windows are not automated.  Having them automated would be fun, but the cost is relatively high, and I keep track of, and limit, the cost of the changes that I have made to a standard production house to one that will meet net-zero source energy, as shown here.  The payback period for the insulated cellular shades was already quite long (35 years) without adding automation.  I do not expect the shades to last as long as the payback period, but the shades offer a significant increase in comfort, help avoid the need for air conditioning, and provide privacy, and these three factors justify their cost. 

Hi Lee Dodge -

You might find Mike's DIY shade/window automation to be inspirational for an upgrade!

Quadomated

In fact, I find Mike, what he has accomplished, and his entire website to be truely inspirational.

This may be a little simplistic, but here goes. Overhangs can be quite short. After the overhang/roof and gutters are in place, build an arbor type structure about 2 or 3 feet wide along the length of the south side. Arbor allows sun to shine through whenever needed. Use shade cloth for the summer. You could unroll 1 ft in april, or 3 feet in June. Early fall cold snap, roll some back up. Or Indian summer, keep it rolled out. Easily variable, just needs to be adjusted a few times a year. Devise a keeper to prevent wind from blowing it away; No one can see my patio, so I just use 3 or 4 cement blocks to weight 30 feet of cloth that covers a patio door and 2 windows, works great. i went real cheap, got recycled billboard tarp that is UV stabilized. $50 worth (24 x 48) will last me about 40 years since one 4 foot wide strip has lasted 4 years already with little damage showing.

I think shadecloth is a great solution for a retrofit, particularly where the existing design makes adding overhangs difficult or cost prohibitive. However, this is much like the wood heating solution where you can't be sure that schlepping the wood will be such a good idea when you are 81 and the next person in the home may not be so adept at playing with shade cloth. New builds should definitely incorporate proper eaves into the plan from the beginning. The extra expense is quite small, and frankly, inadequate eaves come from attempts to short what should have been there in the first place.

Be aware that it is not enough to draw your solar engineering into the plans. It may be necessary to make specific call-outs where construction differs from "standard" practices. For example, When I looked at my under-construction eaves and said "Those look too small; are they correct?", the answer I got back from the framers was "Yeah, they're correct; that's how we always do 'em."

My next comment; "Well, how are they with respect to the PLANSET you are working to....."