Passive-Solar, or Sun-Tempered?

One of our goals in building this house was to be able to live in something easy and inexpensive to heat---an important consideration in Maine. This naturally led us to try to incorporate passive-solar features.

The basic features of passive-solar house design include south-facing orientation, overhangs/shading, thermal mass, sufficient insulation, and energy-efficient windows. Now that the house is coming together, we can see that we have been more successful in incorporating some of these features than others.

We sited the house really well. To take advantage of the sun's heat, a house should be longer than wide, with the long axis east-west, and a long south-facing wall, fitted with lots of window glass situated to absorb the heat from the low winter sun.

Now that the windows are in, we think that we have under-glazed. Since the south wall fronts on a contiguous great-room space that is fairly shallow, we were afraid of overheating, so we were cautious about glazing. We also neglected to consider that the installed windows would actually lose a full two inches in each direction to the frame, so that the actual glass area is 4 inches narrower and 4 inches shorter than we had planned on each window.

On the other hand, we paid really close attention to the angle of the sun and where it hit the south wall in the winter and the summer, and put our glazing high enough to catch the winter sun and avoid most of the summer sun. Our 2.5-foot roof overhangs, also a key passive-solar feature, are integral to making this happen.

Regarding thermal mass: our external walls, with 18 inches of mortar and wood, supply a huge amount of ambient thermal mass. What we are missing is thermal mass specifically located to absorb and moderate the sun's rays. We can still add some in the future, but for now we have decided to forgo extra thermal mass in our internal walls and floors. (We had also decided against a concrete pad foundation, which is a feature of many passive-solar designs.)

Insulation: Our 18" walls contain an average of 8 inches of sawdust insulation. However the value of cordwood lies in the combination of insulation and thermal mass, even more so than in log homes. Nevertheless, I would guess that the insulation alone probably meets the standard for walls, even without considering the mass factor. Our ceiling has standard materials (batts and rigid foam) but at R35, is a somewhat lower R-value than the new super-efficient standards.

Energy-efficient windows: here's where we could have used a bit more education. We thought we had done well, and I was excited at the prospect of new, "Low-e" windows that reduce heat loss through the glass. However, we didn't realize that the windows that were sold to us as energy-efficient were actually "LoE-2" (the "2" is superscripted so you don't really notice it). LoE-2 windows, as it turns out, are manufactured and offered as the "standard" by the major window manufacturers as an attempt to meet the energy efficiency needs of all 50 states. In addition to reducing heat loss through the glass, they also limit solar heat gain by blocking passage of infrared and some ultraviolet rays---a feature helpful in hot-weather climates, but detrimental to a passive-solar design.

So, in the end, our house may end up functioning more as what Dan Chiras terms a "sun-tempered" design than a true passive-solar spacing-heating system. Even so, according to Chiras, a sun-tempered design can take care of 20 to 30 percent of the annual heating load. We'll report back after we've lived there for a while.

Cordwood Commentary

It's worth remembering some of the comments people have made about our cordwood house, while helping us build, seeing finished walls, or watching us work:

"This is . . . different . . . "
"This is awesome!"
"Looks awfully tedious." (our neighbor)
"Won't it shift?"
"Won't it heave?"
"How do you keep the bugs out?"
"How long will something like this last?"
"So . . . you're not going to sheetrock inside?"
"You guys are out of your minds!"
"Pretty zen."
"This is really laborious."
"This is crazy!"
"Looks awfully tedious." (our neighbor again)
"This is so cool!"
"I'm happy for you guys, but I'm not really diggin this cordwood thing."
"It's like a fortess!"
"Me, I like to throw up some plywood, some vinyl, and call it good."
"You'll be able to heat it with a candle."
"Looks awfully tedious.' (neighbor---still)
"When I look at that wall, I think of 101 Dalmatians."

And the best one: "I'd say it looks pretty Zombie-proof."

Tarp House starts to become Sunnywood

Because it's important for the lime-putty mortar not to cure too quickly, we had tarped each panel as it was completed, to protect it from sun wind. So as far as the neighbors could tell, despite all of our building efforts, we still had just a tarp house.

Today we removed the tarps from the panels that we had completed 30 or more days ago (time enough for initial curing): a total of 5 panels. Even though these earlier panels, as the "learning walls," incorporate all of everyone's mistakes, they are still awesome. I can't wait to live in this house.

10th panel is done!!!

As of 5:30 yesterday (Sunday, 9/20) eve. This panel took 16 batches and 3 days for Joe and me, with Heidi working with us for about half of that time. We had our first real frost Saturday night, so we'll have to wait and see if and how that affected the fresh mortar. All of the panels are now tarped and curing. Stay tuned for details and photos about mixing lime putty and mortar, setting window frames, using bottles and other decorative features, techniques for top work, comments people have made, and more.

Going for 10!

Okay, due to popular demand (i.e., both Joe and I think it's a good idea), we have completed panel 9 and begun #10! We have been very lucky to have Heidi back to help us. It took 19 batches and 4 and a half days for panel 9, but the big window frame took a lot more preparation and handling than the smaller frames (that will be another post: how 2 people lift and set these massive frames). Our plan is to be done with the 10th panel, if we push it, by the end of the day on Sunday. Or Monday.

We had a light frost in some spots last night, but covered the new work with tarp.

Trapped in cordwood

Our long silence does not mean that we've finally mortared ourselves into our walls! We're just in a building frenzy, trying to complete as much wall area as possible before the calendar puts an end to it. After that we'll update this blog with detail and process notes and photos.

We finished the 8th panel on Saturday the 12th. We could move in for the winter with 8 panels, as that would give us three "bays" closed in, if we install a temporary wall at the west end of the completed panels. But we made so much progress on the 9th panel yesterday (we're getting better at this, and faster*), that we are now considering the possibility of a 10th, which would give us 4 bays---all of our living area except the utility and project rooms.

See the rough floor plan below. The gray exterior border represents the 18" cordwood wall. The small black rectangles are posts; there are a total of 14 cordwood panels between the posts. We have completed the panels bracketed with red: three on the north, three on the south, and the two large east panels. As of yesterday, we had about a third of the cordwood done on the 9th panel (the next south-facing panel). If we complete another north panel, making 10, we can move our temporary wall west by an entire set of posts.

We've extended our "stop" date to the 19th, which is surely pushing it in terms of approaching frosts. What do you think: is it worth taking a chance that frost might affect the set of the lime mortar?



*Joe and I, working alone, mixed and laid up six batches of mortar, in addition to cleaning some logs and sifting some sand.

Working on panel 6!

Heidi, beginning the sixth panel:

Our post and beam, shed-roofed, 43' x 25' design has 14 infilled cordwood panels between the posts. The minimum number of filled panels we need to be able to live there during this winter is eight: this would give us the kitchen, bath, one bedroom, and a bit of living area. But we can only lay cordwood until about mid-September, because lime-putty mortar doesn't set up well in really hard frosts. So our goal has been 8 panels by mid-September. Looks pretty doable at this point (maybe we can fill 10 panels, which would give us more living area and the other bedroom!).
The following pictures show the fifth panel, which is actually the center panel of the three well-glazed south-facing living-room panels. This went fast because the window frame took up so much room.
Here are Isaac and Heather, completing the top of the center panel. Note Joe's homemade scaffolding:


Check out Isaac's under-the-window cordwood pattern!


Laying a bottle end:



Joe is sitting in the window well. 18-inch-thick walls make window frames with a lot of options! (You can see one particularly bright turquoise bottle end as well.)