Timeline - Design Evolution - Insulation

Past three years

The Choices

As our design evolved, I waffled as much on the insulation as on French drains, the extent and composition of the earth contact walls or the design of the foundation walls. Hands down, spray foam would be the best choice for several reasons and worst choice for several other reasons.  Its positives are a high R value (at 6.5 per inch, it is twice that of most other insulations), it blocks air infiltration and it adds strength and rigidity to the wall or ceiling. Its negatives are that it mostly comes from petroleum (as I understand it, the addition of soy is more greenwashing than creditable), has high embodied energy, out-gases VOC's for a while after application and it is incredibly expensive especially since it is not DIY-friendly and our design for a super-insulated house calls for exterior walls and cathedral ceilings that are extraordinarily thick.

So what else?  My second choice was cellulose for both the walls and the ceilings. The advantages of cellulose are that it is made from recycled paper, which is about as green as it gets, it does a pretty good job of sealing off air infiltration, particularly in walls as thick as ours will be, it can be sprayed into walls before drywalling much like spray foam and it is relatively inexpensive.  There is one important disadvantage of cellulose for our cathedral ceilings -- for a decent R value, it has to be dense-packed which requires the space between the ceiling and sheathing to be entirely enclosed so as to be able to pack the insulation densely. With our mini-attic (cathedral ceilings) design, the space that exists under the sheathing precludes dense-packing.  The same goes for loose fiberglass which would also have to be dense-packed to function well in a cathedral ceiling.  Fiberglass batts, in my opinion, are not an option for super-insulation. However, we may use them for the 6" exterior walls of the garage (but not the wall between the garage and the house that will match the other exterior walls).

Rice Hull Insulation

Since none of the conventional insulations suited our needs perfectly and still needing to reduce costs, I went searching for alternatives.  I had reread Don Stephens' article on Annualized GeoSolar dozens of times but blew off his argument for rice hull insulation as impractical for us. About a year ago, when searching for alternative forms of insulation, I finally Googled rice hulls.  Up pops The Rice Hull House, a slide show on truss walls and rice hull insulation emanating from Washington, LA.  Also I found an article written by Paul Olivier on the  attributes and physical properties of rice hulls.  (I suspect that Paul was the one posting the slide show as well.)  

Price Quotes
After getting a price quote on hulls from a southeast Missouri rice mill that was

considerably higher than the price Paul mentioned in his article, I exchanged emails with him seeking input.  He advised looking further, that they should be available at $15 per ton. A freight quote for a grain trailer-load (18 tons) from Arkansas or Louisiana was $500-900. Eighteen tons at $15 per ton plus freight would run $770 to 1,170 for as much as my rough calculation suggested we would need to do our entire house.   If not, depending on the amount we were short, we would either finish up with cellulose or order another trailer-load.  

A quote for doing the whole house with cellulose was $4,700.  God only knows what it would be for spray foam.  And the quotes would be higher now because our design has recently morphed into walls and ceilings that are several inches thicker.

Properties of Rice Hulls
As explained in the article by Olivier, rice hulls possess a high silicon content which makes them essentially inert when it comes to combustibility, mold growth, vermin and insect support -- even more so than for cellulose.  The thermal resistance (R) factor for rice hulls when poured or blown into a wall or ceiling cavity is R-3 per inch, which is similar to loose fiberglass and cellulose.  Interestingly, Paul also said diatomateous earth can be added to the hulls as a further measure against termites. The earth particles find their way under the insects' shells and abrade them to death.   

Tactical Issues
Since the blower used with cellulose is not robust enough for hulls, a stronger homemade blower is necessary --  as shown in the slide show mentioned above. Chances are we will make a blower but we have also been brainstorming about ways to build walls and cathedral ceilings in non-typical ways in order to use rice hulls 

Insulating a 2 x 4 wall with hulls before sheathing and raising (internet pic)

without a blower. For example, the truss walls (15" thick) could be built in 4 x 8 sections and insulated before raising them. Or the cathedral ceilings could be closed on the bottom using the  already-planned pine tongue and groove wood ceiling, the hulls poured onto the ceiling between the rafters then the roof sheathed and waterproofed -- obviously an upside down approach compared to conventional construction.

Another tactical issue is how to receive the hulls.  Probably we will elect to have

them dumped on a paved parking lot and use Lawn Funnels and lots of volunteers to fill plastic contractor bags..  The bags could then be hauled to the building site, palletized and tarped until needed. Some of the hulls will undoubtedly be poured directly into spaces to be insulated but, realistically, a home-made blower will come in handy.

(Parenthetically, the Lawn Funnel for paper bags is still available but the model for plastic bags has been discontinued.  Fortunately, we have quite a few of the plastic bag model left over from when the Young family still owned the patent for the Lawn Funnel and manufactured / distributed them.)

Timeline - Design Evolution - Energy Efficient Roof

Past Three Years

Cathedral Ceilings

From the beginning, we envisioned cathedral ceilings in lieu of an attic but was unsure as to how they should be constructed to maximize energy conservation. My first choice for the roof-ceiling complex was structural insulated panels but as discussed in the previous post, SIP discussion, they were not budget-able.  So, that's OK -- we'll just throw up some 2 x 12s, sheath and waterproof the tops, drywall the bottoms and insulate in between, right?  Whoa, I was soon to find out that it's not that simple.

Moisture Condensation

Moisture condensation occurs when the ceiling is not air tight, which includes most ceilings.  As air moves from the

Download pic:  2 x 12 rafters for a cathedral ceiling

interior, it takes moisture with it that condenses as it approaches the cold side of the roof in winter, rotting the wood, encouraging mold and lowering the insulation R-value.  And this phenomenon is much more critical for cathedral ceilings than for ceilings under attic space.  The moisture reaching attic space is dried by attic ventilation before it can do damage.  But not so with enclosed cathedral ceilings.

The internet is rife with the pros and cons of using the typical sheathing-rafter-drywall approach for cathedral ceilings.  My interpretation of the chatter is that 2 x 10s or 2 x 12s with sheathing and drywall will work under some circumstances and not others. When urethane-type spray foam fills the space between sheathing and drywall, air infiltration is nil, even without a sheet plastic moisture barrier, so moisture condensation is moot.  But spray foam does not fit our budget.  When it comes to dense pack cellulose or dense pack fiberglass insulation, arguments fly back and forth -- some say they inhibit air infiltration enough that condensation is not a problem and others warn against using them in a closed cathedral ceiling.  Batt insulation is leaky enough that, even with a plastic moisture barrier, is probably not worth the risk.

Mini-Attic with 2 x 12s

Download pic:  Ventilation for cathedral ceiling

The nay-sayers advocate using what essentially is a mini-attic at the top of the rafters to allow any air passing through the ceiling to exit into ventilated space.  Then, even if some condensation takes place, it readily drys because it is in contact with moving outside air. This is the cautious approach I have decided to adopt so we can use any type of insulation and not worry about condensation issues. And, to stop air from entering the ceiling in the first place, I plan to use at least one layer of carefully-detailed 6 mil plastic sheeting as a moisture barrier below the rafters before installing the tongue and groove natural wood ceiling which, unfortunately, has more potential for air infiltration than drywall unless it is backed up by some sort of solid sheet material like 3/8 drywall or Masonite.  (Recent update:  As voiced in subsequent posts, I learned that plastic sheeting above the drywall is ill-advised for our climate; it will not be included in our design.)

To create a mini-attic, I plan to use structural (construction) screws to fasten 2 x 4s on edge and on 24" centers at a 90 degree angle to the

Download pic:  Natural wood ceiling

rafters and fasten the sheathing to them. Then, by keeping the insulation flush with the tops of the rafters, the "attic" will comprise the 3 1/2 inch void between the insulation and the sheathing that will be ventilated through the soffets. I had already planned to use foil-faced OSB board for sheathing in order to reflect radiant heat in summer. It is typically installed with the foil side down, which should also allow it to handle better than the "raw" OSB side of the sheathing any moisture condensation that reaches the mini-attic and takes a while to dry.

R Factor

Since I plan to insulate both the walls and the ceiling with rice hulls that are rated at around R-3 per inch, a 2 x 12 roof gives at least an R-36.  But, consistent with super-insulating, I would like to shoot for R-50.  Consequently, I plan to secure with structural screws a 2 x 4 edgewise to the bottom of each rafter in order to provide for an extra three and a half inches of insulation.

However, the above modality does not address thermal bridging through the rafters.  I plan to handle this problem by ripping 1" thick foam board into strips and sandwiching them between the bottom of the rafters and the edgewise 2 x 4s.  They will also increase the height for the loose insulation by another inch.  The roof will then be at least R-50 with thermal bridging controlled.

Mini-Attic with I-Joists

An alternative choice for a mini-attic system would be 15" I-joists instead of  the stick-built 2 x 12 system described above. The advantages would be simple installation, fabrication from renewable sources and minimal thermal bridging.  Their disadvantages would be greater difficulty mating them to the 15" exterior walls than with the 2 x 12s and higher cost. Not only are the I-joists more expensive than new 2 x 12s per linear foot but the stick-built approach will allow the use of materials recycled from tear-downs for an additional savings.

Recent Update 

Much of the above design became moot late in 2016 when I decided in favor of 16" and 18" tall roof trusses in lieu of joists -- either 2 x 12s or I-joists -- and a double layer of roof sheathing with a 3 1/2" space between layers to serve as a dedicated mini-attic.  Makes me grateful that the building inspector was happy with architectural drawings that were sufficiently nonspecific that I could improvise on the fly.

Timeline - Design Evolution - Stick Built Exterior Walls

Past Five Years

Ruling Out Alternatives for Exterior Walls

One of the first decisions we needed to make was whether to use an alternative to conventional stick building for the non-earth-contact walls.  The options are plentiful -- rammed earth, straw bale, Earthships, adobe, cob, cordwood, earth bags -- to name those that Daniel Chiras covers in his "The Natural House -- A Complete Guide to Healthy Energy-Efficient, Environmental Homes".  

My first choice however was structural insulated panels even to the extent of buying Michael Morley's book on SIPS and getting preliminary quotes from a couple of vendors.

The panels are structural enough to eliminate conventional framing, have built-in insulation, allow no air infiltration, are constructed off-site to cad-cam precision and go up so fast that the house is under roof in a matter of days.  SIPs work especially well with timber framing (most timber-framed houses today are enclosed with SIPs)  but the two together would have exceeded our total budget!  Time to look for an affordable alternative.

Stash of Salvaged Lumber

We are sitting on quite the stash of lumber that I salvaged from old buildings -- three houses, two garages and several outbuildings, plus freebies picked up through Craigslist. Most of the dimension lumber is 2 x 4s which, if installed in the usual way, would not provide the R-45+ wall we need for a super-insulated house.

An important but poorly understood reality is that, irrespective of the R-13 the manufacturer prints on the insulation, the whole wall R- factor for a 2 x 4 wall is no more than R-10 when thermal bridging through the studs and plates is factored in. And that's even before air infiltration enters the equation.  Similarly, due to thermal bridging, the actual R-factor for a 2 x 6 wall is R-14 instead of the  R-19 printed on the batts.

So, how do we build R-45+ walls using the salvaged 2 x 4s?

Double Wall Construction

Early on, I had considered using a double-wall construction which is basically two separate walls tied together at the top and bottom plates with the amount of space between the walls dictated by the R factor goal.  And for the double wall, I was thinking about using 2 x 4s rotated 90 degrees from normal studs in order to reduce thermal bridging and to better manage inconsistencies in the salvaged lumber. However, before I had worked out the details, I made a lucky strike.

Truss Walls

While searching for a cheaper alternative to conventional insulation, I remembered Don Stephens mentioning rice hull insulation in his article on Annualized GeoSolar.  When I Goggled rice hulls, I found a blog that detailed the construction of truss walls in conjunction with rice hull insulation. The blog was posted by a Louisiana company building low-cost, Habitat for Humanity-like, housing using wall trusses filled with rice hulls for insulation (Rice hull house with wall truss design).  The important difference between their trusses and my double-wall idea was that the trusses can be made individually in a jig and assembled in the wall as if they were studs.  This approach is much simpler than building and raising two separate walls then joining them at the plates, particularly for someone working alone.

At the time of this posting, the wall truss jig was nearly assembled in the workshop in anticipation of building the 65 or so wall trusses ahead of time on days too inclimate to work outside. The jig will yield trusses that are highly standardized despite the inevitable inconsistencies in salvaged lumber.

Odds 'N Ends - A Broader View of Sustainability

The Food Chain Starts with Plants
Only plants are capable of converting the sun's energy into food (photosynthesis). Plant-eating insects and animals -- herbivores (with minor input from omnivores) -- convert plant tissue into animal tissue.  Without plants and plant-eaters, there would be no higher forms of life, including humans.  Unfortunately, many plants, insects and animals at the lower end of the food chain are on the road to extinction due to habitat loss and degradation.

In my opinion, anyone interested in a broader view of sustainability should read the eye-opening "Bringing Nature Home - How You Can Sustain Wildlife with Native Plants" by Douglas W. Tallamy, professor and chair of the Department of Entomology and Wildlife Ecology at the University of Delaware in Newark, Delaware.

Three Problems
The gist of the book is that plants capable of supporting the essential herbivores are under assault on three fronts.  First, habitat for natives has been replaced by agriculture, lumbering and urban sprawl (think herbicidal control of milkweed, the sole food for monarch butterflies, and loss of their winter habitat in Mexico due to illegal lumbering). Second, pests that hitch a ride on imported ornamentals cause extinction of natives (think chestnut blight, Dutch elm disease and Emerald Ash borer).  And finally, alien plants, with no natural enemies, out-compete natives (think Russian olive, Japanese honeysuckle and kudzu).

To make matters even worse, alien plants hog resources (nutrients, water and sunshine) but, since they are rarely eaten by native herbivores, contribute nothing to the food chain. The ubiquitous foundation plants, ornamental trees and shrubs, as well as cool weather grasses, are all problematic in this regard.


Habitat Fragmentation - Habitat Islands
Instead of the original thousands of acres of contiguous native habitat, the habitat remaining today is in the form of isolated islands that are usually degraded by alien invasives, foul air and chemical run-off.  "Bringing Nature Home" means gardening and landscaping with enough native plants to support wildlife.  Native trees, shrubs and prairie plants bridge between isolated islands and provide sustenance at the bottom of the food chain that may actually be better than that provided by the islands themselves, particularly in heavily populated areas.  

Co-evolution
Native plants support native herbivores because the plants and insects/animals evolved together over millenia.  The native herbivores do not recognize alien plants as food and, if they were to be tempted, likely do not have the ability, bestowed by co-evolution, to overcome the plants' defense mechanisms.  A white oak tree, for example, supports 534 species of lepidoptera (moths and butterflies) while a Bradford pear tree or Japanese honeysuckle bush support practically none (Tallamy).

Resources 
About half of Tallamy's book is advocative and half is helpful hints for getting started with natives and guidance on region-specific plant selection.  

Wild Ones (www.wildones.org) is an organization that promotes landscaping with native plants and, of course, the eradication of non-natives.  As members for several years, Dorothy and I have visited many beautiful private and institutional native landscapes. And we have mingled with the choir -- a unique subset of interesting environmentalists who are only too happy to share, not only their knowledge, but plant seeds as well.

Our Progress
Although we are at least two years away from completion of our home, we have already eliminated most of the alien plants that overran the property initially. Our new natives are beginning to flourish in areas that will not be disturbed by the construction and their progeny will dominate after construction.

Fortunately, here in the hilly bluffs of the Mississippi River, the habitat fragmentation is less intense than in the surrounding countryside--more like peninsulas than islands. Our hope is that someday our 4+ acres of mostly natives will be a bridge between two adjacent (struggling) peninsulas.

Oh, by the way, did I mention that native gardens and grasses slow global warming? Yep, in two ways--by storing far more carbon than foreigners like fescue, zoysia or Japanese yews and by avoiding the carbon inputs of watering, fertilizing and mowing (Native plants and global warming).

Timeline - Design Evolution - Foundation Walls

Past two years

Uninsulated Foundations
Nothing riles my sustainability sensibilities more than the sheer ubiquity of above-grade block and concrete foundations.  "Walk-out basements", with even more exposure, are prized even if they face northwest.  

Walk-outs facing northwest.

Many newer houses have retrofitted interior insulation, especially for finished spaces,  While better than no insulation, the thermal mass of the concrete ends up on the wrong side of the insulation for maximum performance.

A serendipitous example of heat transfer (conductive heat loss) through an uninsulated

foundation is seen in the photo to the right. Dorothy planted a tropical plant (Christmas cactus) next to the house never expecting it to make it through one winter, much less five. The heat conducted from the basement warms the soil enough for he plant to survive the cold season. In the other picture, notice how the snow melts first near the wall. The tan remnants of the cactus on the ground at the top of the photo indicate dormancy, not death.

Our Problem
Over the past two years, I have spent an inordinate amount of time worrying about the design of the foundation under the stick-built walls.  As our original concept of earth-sheltering morphed from earth contact on the north and west sides of the house into earth sheltering on on the north side only, the need for stick-built walls increased. And more stick-built walls meant more energy-problematic foundation walls.

Protecting the Thermal Mass

A lot of the heat that the AGS System generates and stores under the floor would bleed out through the foundation walls and be lost unless the entire foundation is insulated.  But doing this on a low budget is a challenge.  I looked at several ways.

Dry-stacked cider blocks would work structurally and affordably (per Rob Roy in his book, Earth-Sheltered Houses- How to Build an Affordable Underground Home), but we would be back to the waterproofing and insulating conundrum he wrestles with. The Complete Block System would work well and, like the cinder blocks, would be DIY-friendly but too expensive.  A DIY-poured concrete wall in rented forms would not be a bargain, would be lots of work, would be too tall for the frost-protected shallow foundation (see below) and has the same bad choices for insulating and waterproofing as the cinder blocks.

Insulated Concrete Forms

As it turns out, the best value for the foundation walls for us will be concrete poured in insulated concrete forms (ICFs). Setting up the forms, which stay in place after the pour, is surprisingly DIY-friendly.

The ICF walls with 8" of concrete and 5" of Styrofoam will be about 13" thick and will fit nicely with the width of the stick-built wall trusses above them.  And ICFs automatically provide slab edge insulation.  This is a big deal because insulation of the slab edge is important for energy conservation and is one of the things that green building certifications such as LEED and HERS highly value but something that normally is difficult to achieve in the field.

Conventional Foundation

A conventional foundation wall in conjunction with a slab floor in our climate must rest on a footing, the bottom of which must be below the frost line -- 30" below grade. Without proper insulation, the foundation is an energy nightmare, losing heat through the wall and, in the process, sucking energy from the adjoining slab.

Frost Protected Shallow Foundation

In our situation, there will be a footer and no insulation under the slab

However, if the wall is insulated on both sides and insulation is laid horizontally over the footing at the base of the outside of the wall and extended outward for a couple of feet, the footing becomes frost proof and can be raised above the frost line and the wall on it shortened as well. The result is a "frost protected shallow foundation".

For us, ICFs are a reasonable solution.  They provide the insulation for the wall above the footing while the insulation in the insulation-watershed umbrella for the AGS system serves also as the horizontal insulation over the footing that characterizes the frost-protected shallow foundation.