Construction - Screened Porch Floor

This post focuses on the next-to-last phase of the concrete work, viz., the screened porch in front of the house.  Remember that you can click on any photo to enlarge it for a closer inspection.

Footings and Foundation
I over-excavated the soil next to the house to the level of the foundation footing and then sloped it downhill in order that the insulation/watershed umbrella can installed on top of the footing and sloped downhill enough to drain well.  In the process, the soil under what will be the concrete floor for the 14' x 16' screened porch on the front of the house was also over-excavated.  In order to compensate for the over-excavation, the footing for the porch foundation was much taller than it was wide on the downhill side which complicated forming it up for the pour.

I mimicked the forms we used for the 8" tall footings under the house foundation by using

Forms for the footings

some of the same salvaged 1 x 8s and the same lightweight braces. As a result, we almost had a blowout because the bracing and the 1 x boards were too weak and barely able to hold the weight of so much concrete on the tall downhill side.  Consequently, the footing after the forms were removed looked pretty amateurish. 

Poured footing; notice the bulge just beyond
the corner due to a near blow-out

I thought I had learned my lesson and made sure the forms for the short foundation wall on top of the footing would be, if anything, over-engineered.  Wrong! Despite robust 2 x 4 framing for the plywood form walls, we almost had another blowout.  As soon as we started the pour, a wall started bulging due to weakness of the spreaders that tie the two sides of the form together across the top.  Instead of using 1 x 4s and two 6d nails on each side, I used 1 x 2s and one 16 ga 2" nails from a nail gun. We had to stop the pour while I  added several 1 x 4s in the most susceptible areas and re-nailed the existing 1 x 2s with 6d nails.   If I were to do it again, I would use 1 x 4s and regular nails for the spreaders throughout and 2 x 4 stakes for all of the braces because they can be driven with a sledge hammer to a greater depth than the 2 x 2 stakes that I drove with a heavy hand mallet.  Fortunately, the wall did turn out to show a little less amateurism than the footing.

Poured foundation 

Backfilling
Before the slab can be poured, the backfilling must be continued until the cavity inside the footing and foundation is filled

Backfilled with sand to the height of the footing prior to
installing insulation

to within 5" of the finished floor level in order to support a 5" thick slab.  Also the foundation wall must be insulated in order for it to function as a shallow frost-protected foundation. Then insulation must be used horizontally under the floor as part of the watershed/insulation umbrella. Accordingly, I used sand to fill the cavity to the top of the footings in lifts (layers).  The sand was not wet enough for proper condensation so I hosed it down before condensing it with a manual compactor.  A good overnight rain finished the compaction.  In retrospect, I should have borrowed a friend's plate compactor for better compaction with less effort.

Insulation As Part of the Insulation/Watershed Umbrella
Over the sand, I layered mostly EPS but some XPS foam board following the

Horizontal and vertical insulation starting at the level
 of the top of footing

recommendations of Hiat, i.e., 4" thick for the first 8' out from the house then 3" thick for the next 4' followed by 2" thick. This 4-3-2 pattern was also used for the garage floor as described in the next post. For the rest of the subgrade umbrella on all sides of the house, the pattern changes to 4-3-2-1 in order to reach out a full 20' from the house. 

In order to satisfy the requirements for a shallow frost-protected foundation, the porch foundation must be insulated on both sides.  Inside, I merely stood EPS against the wall. For the outside, I will eventually install expanded polystyrene insulation board 2 1/2" thick supported by metal drywall track and covered with

Form for cantilevering the slab outward
with rebar to support the edge

parged cement board.  (This process was previously discussed in the recent post on the first retaining wall.) For a finished look, the slab will will be cantilevered out over the concrete of the foundation by at least 3" in order to cover the insulation and parged cladding. To this end, I built a peripheral form that would allow the slab to overhang the wall by the width of a 2 x 4 and controlled for height of the slab by way of  2 x 8 sideboards.  In order for the floor to drain southward, the sideboards were installed at the same height as the house floor next to the house then angled slightly downward such that the floor will fall 
1 1/2" over a distance of 15'.

Final backfilling, ready for 6 mil plastic and concrete pour

Slab Floor
After the insulation was in place, I covered it with a thin layer of sand to isolate it from the wind and to buy some time while another rainy period passed.   When the weather permitted, more sand was added in lifts and each lift hand-compacted until nearly flush with the foundation wall, thus leaving space for a 5" thick slab.

Completed slab for screened porch with cantilevered edge

Six mil plastic sheeting was fitted over the sand on the day of the pour. Jamie Schulte, the contractor that had previously poured the wide footing for the tall concrete north and west walls, the walls themselves and the slab for the house, returned to pour the porch floor first then to pour the forms for raising the height of the east wall of the garage.   The next day he came back to pour the garage floor.  The garage pours are the subject of the next and last post on the concrete phase of construction.

Construction - Pre-made Exterior Window-Housing Wall Sections

After considerable research on windows and doors, I decided in favor of Pella fiberglass casement windows and fiberglass doors. (For more details on window selection, see a previous post on window design.) The building code specifies that the total window area be at least 8% of the livable floor area.  Furthermore, 4% of the windows must be operable plus egress-friendly in rooms, such as bedrooms, that do not otherwise have direct access to the exterior.  Our passive solar design that situates all but one small east window in the south wall meant that, to meet code, the windows would have to be large and bunched together.  We meet code by utilizing 9 pairs of windows plus one unit of three windows with each window 3' wide and either 5' or 6' tall.  The size of the windows automatically render moot the egress requirement.

The Pella rep was somewhat taken aback when I specified individual windows instead of enjoying the advantage of pairs of windows being joined at the factory with fiberglass mullions as is typical. There are a couple of reasons for keeping them separate.  First, it would be impossible for me, working alone, to install two heavy windows in one piece -- even the individual windows will be a challenge. Second, cost is reduced by about 10%.   

So let me share how I went about using mostly downtime caused by bad weather to assemble in the shop the wall sections that will house the windows.  Eventually, the sections will in interspersed with individual trusses for a wall thickness of 15" insulated with rice hulls to an R-50.

Jigs To Standardize the Wall Sections

Fortunately, there was enough room on all sides of the table saw to use it to support a jig of about 7' x 8' in size.  I would have preferred to use salvaged lumber for the jig but quickly learned that it was too non-standard. Therefore, I used new lumber to insure that all wall sections would be identical -- square, plumb and level.  And I found out by trial and error that it would take mostly new lumber to standardize the wall sections as well.

It took two jigs to make a wall section.  The first one on the saw (top photo) was used to cut and fit the side of the assembly facing the interior of the house then the cut pieces were disassembled and set aside. Then the same jig was used to cut and fit the side facing the exterior which varied with the interior assembly only in the window sill area.  

The next task was to join the interior and exterior assemblies.  This was done by removing from the saw-top jig the 2 x 4 on the left side of the exterior assembly and matching it with

the left 2 x 4 for the interior assembly that had been set aside earlier. They were transferred to the truss jig that was described in detail in a prior post on wall trusses (second photo).  The left interior and exterior 2 x 4s were nailed together to form a truss then the truss was moved  back to the saw-table jig. The right interior and exterior 2 x 4s were similarly nailed together in the truss jig and returned to the saw-top jig. The final step was to fasten all of the individual pieces together in the saw-t jig to make a three dimensional wall section.

Storage
The wall sections will not be needed for a couple of months so it became imperative to protect them from the elements, particularly since some of the gussets for the trusses were OSB.  I tried first to wrap them in stretch wrap but soon realized that was folly -- it was hard to accomplish and it leaked even in light rain. Instead we moved all of the sections onto the house floor and thoroughly enclosed them with plastic and battened-down tarps.  

The OSB pieces that will line the window openings were cut and stored separately with the intention of adding them later after the walls are raised, thereby reducing the weight of the sections for easier handling and delaying their exposure to the elements as long as possible.  In the same vein, I am erecting the weight-bearing interior walls before assembling the exterior truss walls so as to be able to get the exterior walls under cover as soon as possible after they are in place.

Design - Sustainable Building Practices - Cont'd

The first post on this topic delt with site selection and house size.  Here the intent is to identify sustainable practice goals and see how well we meet them.

Criteria for Selecting Sustainable Methods and Materials

From the outset, we tried to understand what we needed to do to employ carbon-phobic

methods and materials, based on my research in print and online that went back several years, well before we had even bought land.  Here are the major criteria for selecting sustainable methods and materials that I came to appreciate.  Most of them are covered in the two books shown here (click on images to enlarge).

• Embodied energy used in manufacture or extraction
• Embodied energy used in transport to building site
• Amount of finite resources in the material, like petroleum or old-age timber
• Amount of recycled content in the material, like in steel roofing
• Amount of toxic waste sequestered in the material, like fly ash in concrete and drywall
• Recycled material instead of new, like salvaged lumber and old limestone foundation stones 
• Minimal waste of materials during construction, like using dimensions that utilize off-the-shelf lumber sizes
• Advanced framing or better
• End-life disposal:  recycled (steel roofing) vs. landfilled (asphalt shingles)
• Amount of volatile organic compounds (VOCs) in the material, like in adhesives, finishes and floor coverings

Sustainable Practices Discussed in Other Posts

Sustainable practices that we have already employed or will be employing and that I have already or will be discussing in many other posts bear mentioning here again:

• Frost free shallow foundation
• Wall trusses that maximize insulation and minimize thermal bridging
• Hinged fiberglass windows and doors with insulated low-e glass
• Rice hull insulation; R-60 to R-72 walls and ceilings
• Blower door testing for air infiltration
• Slab edge insulation (in conjunction with frost free shallow foundation)

  

  Slab floor construction with slab edge exposed

• Fly ash concrete and drywall
• Framing with wall trusses made from recycled dimension lumber
• Steel roofing and wall cladding
• Passive solar conditioning; no energy-gulping conventional heating or air conditioning (references to the AGS system appear in many prior posts starting with first post on Annualized GeoSolar) 
• Airlock between living space and exterior doors
• PEX plumbing system
• Tankless water heater with underground "homeruns" to hot water faucets
• Low-flow faucets; dual-flush toilets
• Energy recovery ventilator
• LED lighting with motion activated switches and task lighting
• Kitchen cabinets, built-ins and casework from locally harvested hardwoods
• Retaining walls from recycled limestone
• Numerous rain gardens to capture surface runoff until it can soak in
• Landscaping with native plants

Striking a Balance

Unfortunately, we have found it impossible always to follow the best practices for sustainability due to circumstances beyond our control.  For instance, my original plan was to use gravel from recycled concrete for the sub-base under the slab-on-grade floor but the recycler did not have a slinger truck for spreading the gravel.  I thought we would use it also for the driveway but found out that it contains rebar fragments that puncture tires.  We may have trouble buying drywall containing fly ash and the floor was poured too late in the season such that the "winter mix" did not contain fly ash. And I am sure there will be instances when we will have to compromise for budget reasons such as giving up on using a damp-proofing material for the earth contact wall made from recycled asphalt shingles that was several times more expensive with less functionality, as it turns out, than the method we ended up with.

Impacting the Sustainability Movement?
I think most would agree that our project will still set a reasonably high bar for sustainability. As explained in an early post, we understand the limited impact of one little project like ours on the big picture but the chances are it will have some effect. At the time of this writing, (April, 2016) page views (hits) to this blog numbered over 6,000 with nearly a third coming from foreign countries.  The last check before publishing this post showed the following distribution among the top ten countries represented:

               -  U.S.                                              4,148         (69%)
               -  Russia                                             385
               -  Canada                                           147
               -  France                                             143
               -  Brazil                                               126
               -  Ukraine                                           114
               -  Poland                                              99
               -  China                                                67
               -  Germany                                           64
               -  United Kingdom                                 54

The other 700 visits originated from places all over the world like Indonesia, Japan, India, Scandinavia, Africa,  Australia, New Zealand, Turkey and the middle east.  Are we impacting the sustainability movement?  One can only hope that a modicum of folks somewhere have gleaned a few useful grains or at least have begun to think about sustainability.

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Update, summer of 2019:  the number of page views to the blog has grown exponentially until they number just under 100,000. 

Update, summer of 2024:  page views now are 180,000; not overwhelming but, considering the limited audience, enough to make blogging on sustainability worthwhile.

Design - Sustainable Building Practices

Building green is not just about energy efficient windows, low-flow faucets and lots of insulation.  It starts with site selection, continues through construction and culminates with the owners enjoying a low carbon lifestyle indefinitely.

Site Selection

For site selection, an important issue is personal transportation -- by what mode and how far.  An urban in-fill location, such as ours, is preferable to suburban, exurban or rural because it reduces travel to infrastructure such as schools and churches, shopping, work, medical care and entertainment.  Proximity to public transit is also a plus; we are a few blocks from a bus line and a short bus ride from a light rail station.  And what an advantage is has been during construction to have the lumber yard, the rebar supplier, a home center, wholesale plumbing and electric dealers and a farm and home store -- all within a few miles.

Site Stewardship during Construction

Here the issue is minimal site disturbance -- limited excavation and respect for topsoil and trees. Our ranch design surrounded by an insulation/watershed umbrella unavoidably requires much more site disturbance than would a multistory conventionally-built house of similar size.  To our credit, though, the topsoil has been carefully removed and set aside for future use.  And erosion is being controlled by straw bales, silt fencing and a retention pond (which has had to be dredged twice during the first year and a half).

Erosion control with silt fencing, straw bales and a
retention pond.

Site Stewardship Is More Difficult When Working Alone
A distinct negative is that working alone takes a long time and site disturbance is protracted.  In an attempt to ameliorate this problem, construction was halted in late fall so I could use the track loader for some serious dirt work.  I was hoping that before the ground started freezing and thawing I could install the downhill portion of the insulation/watershed umbrella -- that part in front of the house -- so that the slope to the street could be returned to its original contour and native plants could a be started immediately for erosion control. So the considerable excess dirt in front of the house was moved to behind the north wall as the first 5-6' of backfill and the hillside was graded.

My intention was that, as soon as the proper contours have been established, erosion could be controlled with an erosion control blanket with native plant seeds sown under it for germination in the Spring. Unfortunately, unseasonably wet weather around Christmas interfered and we went into a crisis mode to make run-off from our property stay on our property using additional silt-fencing and another dredging of the retention pond. It is now May and pouring the footings, foundation and slab for the screened porch and pouring the garage floor has delayed installation of the umbrella to the extent that any definitive planting in front of the house will have to be delayed until Fall and may have to be annual rye grass as a temporary cover crop until it can be replaced by something better later.  We are committed to native landscaping but now recognize that it may have to be done more gradually than we would like.


House Size Matters
Of course, the larger the house, the more energy it consumes -- both during construction and during its life.  In my view, a McMansion that touts its structural insulated panels (SIPs), its geo-thermal HVAC system, its top-of-the-line windows and, even, its photovoltaic solar panels or wind turbine is nothing but sophisticated greenwashing.  True, such a home is better than a McMansion with no regard to sustainability, but size does matter. 

Each square foot of floor space has an impact on sustainability -- more concrete, more lumber, more drywall, more copper wiring and plumbing, more floor coverings, more insulation, more roofing, more furnishings, etc.  At a minimum, each additional square foot impacts sustainability by way of its embodied energy.  And window size and placement also have a bearing.  Ever notice the expansive windows that face north and west even in so-called "green" houses?  

However, the real impact on finite resources plays out during the life of the dwelling. More space requires more energy to heat and cool, regardless of how efficiently it is done (unless it is done strictly with renewable energy -- which is our case).

Our floor plan is essentially a 2,800 sq ft two bedroom/two bath ranch with a third bedroom piggybacked on as an abbreviated second floor giving total living space of 3,000 sq ft. About 450 sq ft of the 2,800 sq ft slab is non-living space that the principal author of the AGS system calls a "vertical basement" and we are calling "storage".  Another 110 sq ft comprises the entry air-lock which could be considered quasi-living-space. 

If our plan is overly consumptive, the master bedroom and the living room-kitchen-dining room "great room" might be considered somewhat generous. However, I rationalized this bit of extravagance to some degree in the following ways:

• Most of the lumber will be either recycled or grown locally
• The "extra" space impacts sustainability mostly via an increase in concrete for the floor, wood for the ceiling and metal roofing, but concrete does sequester industrial waste (fly-ash), wood ceilings come from plantation-grown trees less than 300 miles away and metal roof panels have recycled content and a recyclable end-life
• The extra space will have no impact on the amount of wiring because the longest circuits were shortcutted beneath the slab using donated wire; the same goes for the supply side of the plumbing
• At our age, we will not be the principal owners of the house -- either through inheritance or sale after we are gone, it will be occupied by younger folks with larger families who will appreciate and enjoy the roominess

However, the justification for the added space that is most defensible is that our passive AGS system will provide zero-energy conditioning year-round for the life of the house regardless of the size of interior space.

The next post on sustainable building practices focuses mostly on the construction phase.

Timeline - Deciding on the Amount of Earth Sheltering

Past Six Years

Earth Contact Walls and Roof
Concrete walls are included in the design of our passive solar home even though their extent is limited to the north wall and about half of the west wall, technically making the design "earth-bermed" instead of "earth sheltered".  The classical earth sheltered dwelling   

had only the south wall exposed.  The north, east and west walls would have earth contact and so would the roof to varying degrees. It took me a while to realize that so much earth contact is not necessary in order to eliminate conventional heating and air conditioning.  As you can see in the nearby photo of the house model that was built nearly five years ago and in the prior post on the house model, the original design called for half of the roof to be earth covered.

Going overboard with earth sheltering at that stage was the result of my confusion about the role of that part of the house envelope not facing south.  I bought in on the idea that maximizing earth contact seals off the hostile external environment and makes the surrounding ground temperature the default temperature for attenuating living space temperatures -- all of

which is true.  It took awhile and considerable research, however,  to realize that the story doesn't end there.  Conventional walls and ceilings can be air-sealed and super-insulated (R-50 range) to ward off the outside environment at least a well as contacting earth does. Then, Hiat's "Passive Annual Heat Storage" and Stephens' "Annualize GeoSolar System, made me realize that earth contact can be severely reduced then intentionally manipulated so as to raise the default ground temperature to a comfortable level for living spaces without any help from conventional heating or air conditioning.  

In addition, there were three practical reasons for downsizing the amount of earth contact.  First was the realization that building a two-story concrete wall using something like dry-stacked concrete blocks (like Rob Roy showed in his book, Earth-Sheltered Houses) was beyond my skill and endurance levels and beyond what any structural engineer would be willing to stamp, especially when half of the wall would be two stories

tall with no bracing from internal T-walls.  And not to mention that our budget made it necessary to limit the amount of concrete work we delegated to professionals. Secondly, there are two options for a roof that is strong enough to support earth, neither of which we could afford. One is concrete supported by concrete or steel (wood is not allowable).  Another is like Roy advocates -- 2-by tongue and groove decking supported by timber framing.  But for our rather large project, the timber frame would have to be professionally done -- again a budget buster. The third reason for avoiding an earthen roof is that, since the roof would not support earth moving equipment, the amount of the labor involved in wheel-barrowing enough soil to cover a 2,800 sq ft roof to an appropriate depth would have been formidable.  

According to printed and on-line resources, water leaks have always been a problem with earth contact roofs, at least in non-desert climates.  But this negative did not influence my decision against earth covering for the simple reason that I think Hiat is dead-on in saying that the insulation/watershed umbrella covering the roof and extending laterally from the house, as opposed to conventional waterproofing applied directly to the deck, is very unlikely to allow roof leaks.  And, since the insulation/watershed umbrella is critical for our AGS system, it would have been carried onto the roof if we had opted for earth contact.

Super-Insulation
The advent of "super-insulated" walls and roofs tipped the scales.  I am betting that our iteration of the AGS system will generate and store as many BTUs as the house will ever need.  So the only issue is to make sure as many BTUs stay in the house during cold weather (and out of the house in hot weather) as possible.  And I am betting that our meticulously air-sealed and super-insulated walls and ceilings will do a better insulating job than the earth contact walls and ceilings they replaced.  

The concrete wall is limited to the entire north side and
half of the west side of the house.  The north wall will
be backfilled to nearly a two-story height over more than
 half its length.

In our case, earth contact is limited to the north wall and half of the west wall. The walls have two functions. One function is to become part of the thermal mass but, in this regard, they are only a small part of a larger thermal mass comprising the soil under a 2,800 sq ft floor plus the soil extending 20' outward from the house in all directions under the insulation/watershed umbrella. The large volume of earth thus encompassed by the system is the primary thermal mass; the concrete walls play a minor role.  Actually, the concrete floor plays a far bigger roll than do the walls by a ratio of 2:1 in terms of earth contact area.  The two thirds of the concrete area that the floor represents lies just a few feet above the AGS conduits and thereby is in position to heat-sink more solar energy than the walls.

The second and most important function for the concrete walls is to serve as a heat transfer medium between the soil behind and west of the house and the interior environment.  For this reason, the inside of the walls will always remain unobstructed and accessible to air movement.  Situated just inside the north wall and part of the west wall of the house will be the utility area (aka, "vertical basement" by Stephens) which means that storage shelves will be attached to the stick built walls opposite the concrete walls in order to keep the latter completely exposed for transferring heat.

Design - Rice Hull Insulation

SPOILER ALERT -- Winter 2025

Do not use rice hulls for insulation without reservation.   We did and are not sure as of this writing it was a wise choice.  

As a methodical and cautious early adopter, I thoroughly researched rice hulls and thought I understood the risk of rice hull weevil infestation.  My contact person at the mill assured me that weevils cannot survive the parboiling of the whole grain that is done before separating it from the hulls.  In the absence of any information to the contrary, despite considerable research, I decided to take a chance on them.  

My research told me that weevil reproduction required a grain of rice into which an egg is laid and the larva develops until emerging as an adult weevil.  In the process. the rice grain is consumed.  If there were rice grains in the sample bag of hulls sent by the mill, they were so inconspicuous we did not see them.  Consequently, we assumed that, even if a few existed in the insulation, they would soon be consumed by baby weevils until no more grains existed.  Besides we did not see any weevils in the sample, although, in retrospect, they were much tinier than we expected and were simply overlooked. 

My research also revealed that diatomaceous earth is an insecticide for bugs with exoskeletons by finding its way under their skeletons and dehydrating them.  So a cup of diatomaceous earth was mixed with each bag of rice hulls as they were blown into he wall and ceiling cavities, all the while thinking that this extra effort was probably overkill but advisable since the stakes were high and our knowledge so limited. 

Three years later, we are beginning to think that we know more about rice weevils than those speaking and writing about them at the time we did our research.  Clearly they reproduce in the absence of rice grains.  The "hulls" would have had to include a huge amount of grain in order to support such exponential infestation.  Moreover, we are not only seeing a large number of adult weevils outside the confines of the wall, principally on the window sills, we are seeing quite a few viable larva a well.  They are larger than most adult weevils, but since they have no means of locomotion, they must be transported out into the open by adults.

A major oversight on my part is that diatomaceous earth as a backup would prevent an infestation.  However, the adults obviously live long enough to reproduce before dehydrating and the eggs each female is capable of laying numbers in the hundreds.  Therefore, new bugs are developing faster than the old bugs are dehydrating.  I must say that the vast majority of adults that we see are dead, many with their feet in the air.  So it is safe to assume that, no sooner do they emerge into the open, they die from dehydration.  Supposedly most are able to fly but we see very few actually doing so, although some of those on the sills flap their wings like they are trying.  But, even when prodded, they are so debilitated as to be incapable of flying.

In our situation, it would seem that the weevil infestation should abate due to the limited number of rice grains sealed up in the envelope of the house that are available for food and for egg-laying (which is a different situation than weevils in a granary where there is plenty of food and egg-laying possibilities are infinite).  At the time of this writing, this seems to be the case.  The holes in the window sill sheathing that were necessary to deliver the hulls to the spaces under the windows should have been sealed with foam insulation before the sills were installed.  They were the only major patent openings in the envelope through which the weevils could escape.  So, window-by-window, we have removed the trim and sealed the openings. It is now rare to find weevils.  However, electrical boxes in the walls and ceilings are only remaining unsealed penetrations in the envelope such that it may yet be necessary to access the boxes and obliterate the spaces around the wires entering and leaving them. 

Over time, watch this space for updates on the weevil problem. 

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                                                ORIGINAL POST

Why Rice Hull Insulation?

The short answer is economy.  The rice mills have a hard time disposing of the hulls so they are only too happy to sell them by the truckload cheaply.  In fact, the cost of the hulls is

insignificant compared to trucking costs from the Mississippi delta (Missouri boot-heel, Arkansas, Mississippi or Louisiana) to our St Louis area.  But there are many other advantages of rice hulls over conventional insulation which are covered in this longer-than-usual post.

(From a sustainability perspective, cellulose is the best choice among low-cost conventional insulating materials.  Therefore, it is the one most used in the following paragraphs for comparison to rice hulls.)

Rice Hull Properties

My serendipitous discovery of rice hulls is explained in a previous post --  design evolution - insulation.  My new awareness then lead to the definitive paper on the rice hulls for insulation by Paul Olivier, PhD, "The Rice Hull House".  The information below comes entirely from his paper including the following quote from the opening abstract. 

"The rice hulls are unique within nature.  They contain approximately 20% opaline silica in combination with a large amount of the phenyl propanoid structural polymer called

lignin......Recent ASTM testing.....reveals that rice hulls do not flame or smolder very easily, they are highly resistant to moisture penetration and fungal decomposition, they do not transfer heat very well, they do not smell or emit gases, and they are not corrosive with respect to aluminum, copper or steel.  In their raw and unprocessed state, rice hulls constitute a Class A or Class I insulation material, and therefore, they can be used very economically to insulate the wall, floor and roof cavities....."

Olivier's paper goes on to explain in detail why rice hulls are ideal for insulation. Their R-value compares favorably with cellulose and loose fiberglass at a value greater than R-3 per inch. Their natural fire resistance precludes the addition of large quantities of flame and smolder retardants as with cellulose.  Nor is the addition of anti-fungal agents necessary since the amount of moisture absorbed from the air is very low compared to most organic materials that moisturize in equilibrium with the surrounding humidity.  The high concentration of opaline silica on the outer surface of the hulls makes them very hard but, lignin within the hulls adds flexibility and elasticity, making them far more resistant to settling and compression than cellulose. Also their "tiny tips, edges and hairs interlock........( to produce a) peculiar bonding of rice hulls under mild pressure......(such that) no further settling is possible". According to Olivier, cellulose, can settle "as much as 25%" despite stabilizing additives such as (un-green) polyvinyl acetate or acrylic adhesive.  Finally, "since rice hulls require no shredding, hammer-milling, fluffing, fiberizing, binding or stabilizing, they possess far less embodied energy than even cellulose".  And they are durable enough to be recycled indefinitely.

Freight Costs 
Olivier goes on to analyze the total cost -- hulls plus transportation.  "At an installed density of 9 lbs per cubic foot, one ton of rice hulls will insulate 222 square feet of a 12-inch wall cavity........A standard 53 -foot trailer attains optimal transport efficiency at its maximum legal weight of 24 tons.  If.......we pay an average trucking fee of $1.45 per mile, it would cost approximately $15, $30, $45, $60, $75 and $90 to transport one ton of rice hulls 250, 500, 750 1000, 1250 and 1500 miles respectively.......the (freight) cost per square foot would be $0.07, $0.14, $0.20, $0.27, $0.34 and $0.41 respectively.......Those living less than 200 miles from rice hulls should have a hard time justifying the use of any other type of insulation material".  

He goes on to say that, even if the hulls cost $25 per ton (five times the cost at his location in Louisiana at the time the paper was written),........the purchase price of the rice hulls per square foot of wall insulated is on $0.11.......(when this price for the hulls is added to) the cost of transport over these same distances, we arrive at a total cost (per cubic foot of wall space of) $0.18, $0.25, $0.32, $0.38, $0.45 and $0.52 respectively".  (In this analysis, cubit foot is interchangeable with square foot because the wall thickness is 12".)

Cost Comparison with Cellulose
Olivier says that "cellulose insulation in a dense-pack application (reaches) a density of approximately 3.5 lbs per cubic foot (and) will insulate 571 sq ft of our proposed 12-in thick wall.  At an average delivered price of $540 per ton, cellulose insulation costs roughly $0.95 per sq ft of wall insulated........roughly five times the price of rice hulls transported 250 miles and twice the price of rice hulls transported 1,500 miles".

Real Costs

Rice Hulls:    When I called the rice mill in SE Missouri that was the closest to Collinsville three years ago, the price for the hulls was $94/ton.  When I emailed this figure to Olivier, he assured me that they could be bought for $15/ton.  Indeed, the company that handles the rice hulls for a large rice co-op recently quoted me $15 out of Greenville, MS.  

Deck of a walking floor trailer

Freight:  The actual costs for us will be more than Olivier's paper would suggest due to higher freight costs-- the trailer capacity is less and the per-mile rate is higher than his analysis.  The fluffy hulls are hauled in enclosed 53 ft trailers with "walking floors". Instead of a dumping action, the trailer deck has three sets of slats that move in a coordinated manner such that load is conveyed towards the rear of the trailer until it falls out. Unfortunately, the trailers actually hold only +/-18 tons instead of the 24 that Olivier described and, since truckload freight rates are based on mileage, less tonnage means higher trucking cost per ton. Accordingly, It will cost about $3,600 to ship 18 tons the 450 miles to Collinsville or $8/mi instead of the $1.45 that Olivier used for his examples.  I checked with a local trucking company only to find that, since its grain trucks have half the capacity of the walking floor trailers, trucking cost from Greenville would be higher due to having to make two hauls instead of one.  I hope that, when it comes time to buy the hulls, more research and comparison shopping will turn up a source closer to home that will save on transportation.

Total cost:   Our cost for a trailer-load will be 18 tons x $15/ton = $270 plus $3,600 for freight, making a total cost of $3,870.  If, as Olivier says, a ton of hulls will insulate 222 cu ft of wall space, 18 tons will do just under 4,000 cu feet.  If we were to insulate the garage walls with hulls as well as the house, we would need about 2,400 cu ft for the walls and 2,800 for the ceilings or 5,400 altogether.  This means one trailer-load will not meet our needs and supplementing with conventional insulation for the garage will be necessary.

Cost comparison with cellulose:  In 2013, a local insulation company quoted our project when the design was still in flux to the extent that we were at a ceiling thickness of 12" instead of 15" and a wall thickness of 7 1/2" instead of 15".  The quote for dense pack cellulose was $4,700.  Extrapolating, our current design would have been quoted at $6,130 (plus 3 years of inflation).  This amount would be more than a third higher than insulating with hulls.  This amount also figures out to be $1.23 per cu ft which is a little more than 20% higher than Olivier's figure of $0.95.

Weight Factor
Rice hulls at 9 lbs per cu ft are almost three times as heavy as cellulose at 3.5 lbs per cu ft. Although Olivier does not discuss the weight factor, it seems reasonable that half-inch drywall screwed to rafters or joists would not adequately support hulls piled thick enough for a high R-value.  Either the drywall would have to be thicker or applied in layers.  In our case, tongue and groove pine ceilings were already planned before considering rice hull insulation so the weight factor will be moot. However when estimating rice hull insulation, I think the cost of a more robust ceiling should be factored in.

Non-monetary Advantages 
The numerous advantages of rice hulls compared to cellulose are covered above in the paragraph about their properties.  Another advantage they have for our DIY project -- and I consider it to be very important -- is that they can be installed incrementally in conjunction with building the walls and ceilings as opposed to an all-at-once job by an insulation company.  For example, the walls can be filled as the drywall goes up and the cathedral ceilings can be filled as the tongue and groove pine is installed.  With visual access to the cavities, the chances of voids will be minimized.

Our Plan

Our plan is to use a blower to fill the walls and ceilings. However, the blower used for cellulose is not strong enough for hulls so a custom blower will have to be assembled similar to the one shown in Paul Olivier's slide show on the Rice Hull House concept. As to where to store the hulls between delivery and installation, my current thinking is to have them dumped onto the slab floor of the future garage then protect them with a tarp while we rush to get the garage undercover.
_________________

Update November 2020

We are finally in the process of insulating with rice hulls in ways that resemble the plan just described very little.  Here is the link that will bring the reader up to date --  The Planning Stage.  It is the first of several posts explaining the surprises we encountered, like sticker-shock on the price of the hulls, dealing with the rice weevil infestation issue and how incredibly dusty the hulls were coming out of the blower hose, as well as atypical structural modifications and drywalling sequencing that were mandated by the hulls.  And one of the posts parses the advantages and disadvantages of using rice hulls for insulation versus cellulose. 

Construction - The First Retaining Wall

Our plans call for four retaining walls with the first one next to the west concrete wall being the most challenging.  It needed to be 4 - 6 feet high and insulated and waterproofed as part of the insulation/watershed umbrella.  The insulating and waterproofing were a challenge while building the wall was easy, thanks to 9 energetic volunteers.  But that's getting ahead of the story.  (Click on the photos to enlarge them for more detail.)

Insulating the Concrete House Wall
The first book I bought when contemplating an energy neutral home was "Earth Sheltered

Wall insulation in place

Houses" by Rob Roy.  Through it I learned early on that insulation should be inserted between a retaining wall and a concrete house wall in order to keep the retaining wall from sucking heat from the house.  In our case, I was already planning to insulate the concrete walls of the house that would not protected by the insulation/watershed umbrella. Since the umbrella will dip down behind and go under the retaining wall, the house wall adjacent to the retaining wall will fall outside the umbrella and would need to be insulated.

Cementitious board before adding the lower section

The exact way I insulated the house wall will be covered in detail in another post but suffice to say at this juncture, I used 3 5/8" steel stud track to support 3 1/2" of expanded polystyrene for an R-15 on the outside of the wall.  (The inside of the wall will be insulated in a similar fashion eventually for a total of R-30.)  I then fastened 1/2" old-fashion, heavy, hard-to-cut cementitious board and parged it with top-coat stucco, the latter primarily to cover the junctions between boards and to make the exposed areas of the wall more aesthetic.  Six mil plastic separated the

Wall parged to height of retaining wall;
horizontal insulation in place (part of
which already covered with sand);
vertical insulation supported from
 behind with steel fence posts

galvanized steel from the concrete on one side of the insulation and from the cementitious board on the other side.  Six linear feet of the wall were insulated and covered from the top of the wall down to meet the horizontal insulation already in place over the footing.  

Integrating the Retaining Wall with the Insulation/Watershed Umbrella 
As part of the Annualized GeoSolar system, the insulation/watershed umbrella should extend 20' outward from the house in all directions.  On the west side of the house, it has be convoluted in order to accomodate the retaining wall.  Above the wall it will slope gradually southward

Insulation wired to
steel fence posts

towards the wall then, dip sharply downward behind the wall, go under the wall and finally blend with the umbrella in front of the house. 

I smoothed out the soil under the wall then covered and leveled it with sand to provide a base for a 4' wide wall. Next, I laid down plastic sheeting (6 mil) such that it extended several feet beyond the prospective wall in the up-slope and down-slope directions.  Then came a thin layer of sand over the plastic where the wall would rest followed by two panels of 4' x 8' x 2" insulation board next to the house and another panel of 2" lateral to it such that the insulation under the wall would be 4" thick for the first 8' then 2" thick for the last 8'.  Ideally, the insulation should have extended 4' further to satisfy the 20' width for the umbrella but the original excavation did not accomodate it.  

Three layers of plastic -- one between
insulation and soil contact then two
between insulation and the outside
environment

The vertical insulation was also 4" thick for the first 8' from the house then 2" thick for the last 8'.  To support it, I drove four steel fence posts into the ground behind them and wired the insulation to them.  In retrospect,  all of the insulation should have been the stronger extruded polystyrene (pink) instead of expanded poly (white), especially the vertical pieces, one of which cracked while building the wall and had to be held together by hand until it could be supported by sand in front and dirt behind.

I next liberally covered the horizontal insulation with sand and added two more sheets of 6 mil plastic with a layer of sand between them. Finally, I covered the plastic with a heavy layer of sand into which the stones of the wall could be nestled without damaging the plastic.

Building the Retaining Wall
Three or four years ago, we salvaged foundation stones from a 19th century barn in such

Some of the volunteers at work

quantity that we do not have to use them in a miserly way. Consequently, I decided to make the wall massive enough that the rocks could be laid randomly and still resist the pressure of the backfill behind it.  The final dimensions were roughly 4' wide at the base, 2' wide at the top, 5' high and 16' long.

A view from the loader; step-son Keith
(left) and my good friends Dave and Pat
lifting rocks out of the bucket

The wall came together in less than three hours.  As fast as I could track loader the rocks to the wall site from the rock-pile, the volunteers could set them, including packing sand into the crevices between rocks, laying a sandy base for the next level and compacting the sand with hose water.  Some of the stones weighed quite a bit north of 100 lbs so I was more than grateful for the help. (Parenthetically, the crevices between the rocks will be filled someday with plants native to our area.)

The result

Backfilling Behind the Wall
Backfilling immediately before it rained was critical otherwise water pooling behind the plastic might create sufficient hydraulic pressure to move the wall. I did the backfilling the same day the wall went in. As it was filled, the grades next to the house wall and the rock wall were intentionally tilted to create a swale for carrying runoff safely around the retaining wall.  As the back-fill settles over time, it may have to be tweaked to protect the wall.

Initial backfilling

  
Eventually, the umbrella and a couple of feet of topsoil will be added over the initial backfill after which the rock wall will be protected from runoff permanently. However,  chances are the wall will need a couple of courses of stones added on top to accomodate the horizontal insulation in the umbrella and the topsoil over it.  It also looks as if I should have made the black damp-proofing membrane higher on the concrete wall.  Not to worry, it can be extended later.