Construction - Insulation/Watershed Umbrella for the Annualized GeoSolar System

The insulation/watershed umbrella is a concept advanced by John Hiat in his self-published book, Passive Annual Heat Storage:  Improving the Design of Earth Shelters".

The book is mandatory reading for anyone contemplating a project like ours but it is out of print and apparently available only secondhand online. Don Stephens later improved (in my view) Hiat's PAHS --  including Hiat's umbrella concept, -- and called his iteration "Annualized GeoSolar" (AGS) (also check out  three prior posts on AGS:  first post, second post, third post (the third post zeros in on the insulation/watershed umbrella)).

I began excavating for the umbrella at Thanksgiving-time so it is uncertain how much of it I can do before winter weather interferes.  The umbrella adjacent to the concrete walls will have to wait several months until the tops of the walls between the umbrella and the mudsills are insulated on the outside then backfilled to the level of the umbrella. 

Priority Dilemma
My concern is that all of the footings are protected from freezing this winter by completing the umbrella (highly unlikely) or burying the footings under at least 3' of dirt (behind the north wall) or with some other stopgap measure.  As it turns out, I resorted to covering the exposed footings with EPS foam insulation board with the intention of using the boards later to insulate the concrete north wall in the area of the garage.  Unfortunately, the umbrella will have to wait until after the Spring rainy season.  

Actually, a higher priority for what good weather we have left before the ground freezes is to remove the superfluous dirt from in front of the house in order provisionally to restore the pre-construction contour of the slope.  The grading will be finished in conjunction with installing the AGS umbrella in late Spring.

Most of the superfluous dirt came from the final grading for the floor of the
house but considerably more came from excavating for the AGS umbrella.
(Click on the image to enlarge it.)

Superfluous dirt has been moved behind the wall as backfill.

The backfill against the wall is +/- 6' deep in the middle and sloped
towards both ends for surface water drainage; notice  the AGS
conduits protruding upwards; after backfilling against the wall,
the remainder of the dirt from in the front of the house was stacked
to the right of the conduits to a height approximating the final
 backfill level when it is extended all of the way to the wall;
 eventually, the conduits will have to be extended even more in
order to reach daylight through the taller backfill.

Composition of the Insulation/Watershed Umbrella
The umbrella will be merely a "sandwich" made up of plastic sheeting, rigid foam insulation board and sand.  Starting at the bottom in the order in which the layers will be built up, the sequence is as follows:

• Sand over the soil to create a smooth bed on which to lay the umbrella
• 6 mil plastic
• Thin layer of sand
• Mostly expanded polystyrene insulation board; some extruded polystyrene board
• Thin layer of sand 
• 6 mil plastic
• Thick layer of sand
• 6 mil plastic
• Thin layer of sand
• Two layers of recycled synthetic carpet upside down
• Topsoil

I will be layering the plastic and insulation precisely as Hiat recommends except, of course, we have no earth sheltering on the roof.  Stephens' influence will be represented by the carpet overlay to protect the sandwich from

Illustration from Hiat's book (click on picture to magnify the details)

mechanical damage from such things as burrowing critters or thoughtless use of shovels and other tools.  It will also protect somewhat against the penetration of plant roots although the latter will mostly be inhibited by the fact that the only area that is not too dry to support them will be above the first layer of plastic.

As recommended by Hiat, the insulation will be thickest near the house and thinnest at the periphery in five steps corresponding to the width of 4' x 8' foam board --   4" thick for 8 ft,, 3" for 4 ft,  2" for 4 ft and 1" for 4 ft -- making the umbrella 20' wide. Where a single sheet of plastic is not at least 20' wide abutting sheets will be shingled with a large overlap. The sand is important for a couple of reasons.  First, to provide smooth interfaces between the layers and eliminate air spaces that might allow the umbrella to be damaged by heavy equipment or vehicular traffic, particularly punctures of multiple layers of plastic at the same place allowing through-and-through leakage. Second, to hold the plastic sheeting apart enough that any water finding its way through one layer is sure to flow downhill through the porous sand to the periphery.  Without the sand, the backfill over the sandwich would compress the plastic layers together and trap water, particularly where the plastic extends beyond the insulation.  The umbrella will slope away from the house in all directions and, in some places, end in a mini-French drain for faster drainage ("drainage gravel" in the illustration).

The white expanded polystyrene (EPS) foam board will suffice for all areas except under the driveway and the garage floor where pink 250 psi extruded polystyrene (XPS) will be a better choice for supporting vehicles.  The sand in the sandwich will go a long way towards stabilizing and supporting the weaker EPS. The two reasons for selecting EPS for most of the umbrella insulation are price and EPS's long history of use in wet environments (think insulated concrete forms and flotation for boat docks). I trust that the plastic sheets will keep the foam pretty dry but there will be a few small leaks inadvertently created during installation that will admit trickles of water through a given layer that will have to travel in association with the foam and sand layers to an exit at the periphery of the next layer of plastic, so it is prudent to anticipate some exposure to moisture.

The reason for the plastic is to keep the soil under the umbrella dry.  Doing so lowers its thermal conductivity and inhibits transfer of heat from the thermal mass to the outside environment.  Through dry soil, it takes 6 mos for a unit of heat to move 20' which is the basis for making the umbrella 20' wide.  As Hiat explains, even if some moisture would somehow find its way through three layers of plastic, the negative impact on the ground below would be inconsequential, that the saturation would be so spotty and limited that it would not be enough to compromise the efficacy of the AGS system.

Garage Serves As Part of the Umbrella

Insulation of the wide footing is completed by the addition
of  XPS foam board horizontally; it was covered with sand
before the backfilling; EPS would have worked as well

The entire floor of the garage will be insulated for a couple of reasons. One is to complement the other measures that will make the garage warmer, viz., the insulated foundation, the thick walls and ceiling filled with insulation and the insulated overhead doors. The other is to serve as the umbrella for the north half of the east end of the house.  

In order to fulfill the requirements for a frost-protected shallow foundation, the garage foundation footing below the insulated concrete forms will have to be insulated where it is not protected by the house and garage floors or the umbrella next to the south half of the east end of the house. Likewise, the wide footing for the east end of the concrete wall was poured against vertical insulation but it needed to be insulated on top, which was simply a matter of fitting foam board over it, sandwiching it between two thin layers of sand (to carry any water from behind the damp proofing membrane to the footing drain) and backfilling over it. Eventually, a retaining wall will be resting on it.  

Horizontal insulation in place and the backfilling started

I insulated the narrow footing under the garage foundation in conjunction with extending the footing drain to daylight downhill. I enlarged the overdig next to the footing so that it would accomodate foam board 3' wide and embedded the drain in sand, much like along the backside of the wall, screeded the sand level with the top of the footing and laid in the insulation. I did the same procedure for that part of the front footing for the garage that will not be protected by the umbrella, except there was no drain to worry about and the EPS was only 2' wide since it faced south and direct sunshine should warm the backfill enough to make for a warmer footing anyhow.

The footing drain at the other end of the house merely needed to be extended downhill to daylight, bedded in sand and backfilled.  

The extension of the footing drain for the west concrete wall.

With respect to the exposed footing inside the garage that will be covered by the floor eventually, I used soil to fill the overdig flush with the floor grade and laid foam boards against the north wall and the insulated concrete forms for the other three walls and weighted them down with stones. That should protect the footing this winter; the floor will go in next summer.

For some reason, the follow-up post on construction of the insulation/watershead umbrella was posted out of sequence and is dated 11/28/15.  Please drop down four or five posts to find it.

Design - Exterior Walls

Priorities

Being on a strict budget will precipitate a lot of compromises.  However, one issue is not negotiable and that is a super-tight and super-insulated envelope for the house.   Probably this means we will have laminate or wood counter tops instead of natural or man-made stone, or site-made interior doors instead of prehung, but that's okay.  Energy conservation will remain our highest priority.

Stick-Built Walls Using Salvaged Lumber

In a perfect world, we would be using structural insulated panels or insulated concrete forms for the exterior walls but they far exceeded our budget and are limited on  the amount of insulation they can provide.  And we have a lot of free
salvaged dimension lumber that would go to waste if it were not used for the exterior walls.  The trouble with salvaged 2 x 4s however is that the nails often split the ends during the salvage process, especially when toe-nailed.  Typically, a couple of inches must be sacrificed from one or both ends of the boards during the denailing process, resulting in many studs that are too short for typical 8' wall construction.

Wall Trusses

Early on, I decided to use wall trusses instead of individual two-bys as "studs" for several important reasons.  One, with trusses, the salvaged 2 x 4s could be utilized for an 8' wall even if shortened as long as they remained at least 93" long.  Two, some of the 2 x 4s were not entirely straight (but neither is a lot of new lumber these days) but could still be utilized quite well for trusses.  Third, trusses would essentially eliminate thermal bridging. The last and most important reason for using trusses is that R-value for the walls is directly proportional to the thickness of the insulation and trusses can be designed to house whatever thickness of insulation needed to hit a given R-value target.

Truss Design

The 2 x 4s in the trusses will be turned 90 degrees from the way a stud normally sits in a wall and arranged in pairs, one facing outward and the other inward.  They will be tied together with short  2 x 4s at the top and the bottom and braced with three pairs of gussets cut from 3/8" or 1/2" plywood or OSB.  When arranged in the wall on 24" centers, the result will be a wall filled with 15" of insulation and virtually no thermal bridging.  What bridging does occur will be limited to the short 2 x 4s at the tops and bottoms of the trusses and through the skinny gussets.

As far as straightening the boards, my original idea was to assemble them at the tops and bottoms with the bows pointed away from each other.  Then I planned to use clamps to pull them together until they fit the precut gussets.  Once the gussets were attached, the truss would be straight.  

Using Jigs
However, while researching rice hulls as insulation, I came upon a most interesting

Wall truss jig

slide presentation  (Rice hull house) showing the use of wall trusses similar to what I envisioned but being built in jigs for ease of construction and for standardization.  At the time of this writing, a jig was already in service (the subject of another post) that facilitated any straightening that needed to be done.

Top and Bottom Plates
Characteristically the top and bottom plates are as wide as the wall is thick, e.g., 2 x 4s for 3 1/2" walls and 2 x 6s for 5 1/2" walls.  Unfortunately, the plates then become conductive thermal bridges because they are exposed simultaneously to both the exterior and interior environments.  In order to solve this problem, our 15" walls will have double 2 x 6 mudsills side-by-side and  2 x 6 top plates that are double in a side-by-side sense as well as two courses on top of each other in the typical fashion.  The side-by-side configuration of the mudsills and the top plates will allow 4" of insulation between them, thereby arresting thermal bridging. 

Design - Windows and Doors

Even with our tight budget, we intend not to compromise on window and door quality because they are the weak link in heat transfer in and out of the building envelope.  For example, the R-value of double pane glass is a paltry 1.5 - 2 while the R-value for our exterior walls will be over 45.  The best way we can maximize the thermal performance of the windows and doors is by controlling air infiltration between the wall framing and the window.and between the window frame and the window sash.  Then we need to control thermal bridging through the window frames and through the glass itself.

Air Infiltration
The two ways air infiltrates windows is between the window and the framing and between the window sash and the frame.  In order to hold the window back from the plane of the exterior wall (see below), we will have to use replacement windows that do not have nailing flanges like that of new construction windows.  Nailing flanges are the first line of defense against air leakage between the window frame and the framing.  We will have to compensate for the lack of flanges with caulking and minimal expanding foam insulation and precise fitting of the inside and outside trim.


Air infiltration between the frame and the sash is easier to fix.  Instead of sliding windows

Casement window

(single- or double-hung or horizontal sliders) we will use hinged windows that close against and compress a semi-rigid air seal that doesn't leak. Sliding windows are built with more tolerance between the window and the frame in order to facilitate sliding.  The air sealing is done with flexible air seals that tend not to be as airtight. For us, all but a couple of windows in the garage will be casement windows.

Thermal Bridging

Thermal bridging, a form of conductive heat transfer, occurs through both the glass and the frames.  Double glass marginally improves the R-factor of single pane glass by providing a dead air space between the panes.  An R-2 is not much to write home about. Since windows are essentially poorly plugged holes in the wall, a better strategy is to limit the number and size of windows, particularly on the north and west sides of the house (US Midwest).  Except for two or three small windows on the east, two of which are in the garage, all of our windows will face south.

The addition of argon gas between panes of glass also helps to reduce thermal bridging by impeding convection currents in the space between panes. The literature in my library and online information lead me to believe that argon is more hype than help because it escapes within a few years and therefore is not a good investment.  Recently, the sales rep for the window company that will supply our windows convinced me otherwise. The argon in his windows is guaranteed to be 80% effective for the first 20 years and costs only about $10 per window.  That sounds like a good investment after all.

Thermal bridging through the frame is easier to control than bridging through the glass by choosing materials that have low thermal conductivity.  Fiberglass and vinyl are better insulators than wood and wood is better than metal so, if our budget allows, we will opt for fiberglass for both windows and doors.  If not, vinyl will be a reluctant second choice at least for windows.  Nevertheless, choosing vinyl would be a double-edged sword from a green building standpoint; while it  minimizes thermal bridging it comes largely from petroleum. Fiberglass is a green choice for three additional reasons:  (a) it has the same coefficient of thermal expansion

Proprietary graphic comparing coefficient of thermal expansion 

as glass so the seal between the panes and between the panes and the frame lasts longer, (b) it is many times stronger than

Another proprietary graphic showing the strength of fiberglass relative to vinyl 

vinyl and (c) it is greener because it is made from the most abundant resource on earth -- sand. Also, we will specify warm edge spacers between the panes, which, at nominal cost, reduces thermal bridging through the edges of the glass.  However, we will not opt for fully insulated frames because the payback is not as quick here as in northern climates.

Winter Winds
Glass that directly faces winter winds is considerably more conductive than glass on the leeward side of the house because the wind removes the thin layer of insulating air on the exterior surface of the glass (wind-washing), thereby accelerating the loss of "fresh" heat through the glass.  We plan no windows directly facing the prevailing winter winds. Our exterior walls will be 15+ inches thick which will allow us to recess the south-facing windows into the wall as much as 6" thus sheltering them from wind-washing more than if they were mounted flush with the wall.

The fact that the house will be earth sheltered on the north side and half of the west side will pretty much neutralize cold winter winds.  Nevertheless, soon after purchasing our property years ago, we began establishing a shelter belt north and west of the future house as another buffer.  And the eastern red cedars that we planted are native to our area and very beneficial for wildlife. 

Tinting and Low-E

Exterior overhangs will shade the windows from the summer sun but will allow winter solar gain.  The gain will be maximized by using clear glass instead of tinted glass. However, we will specify a low-E coating in order to slow heat loss out through the glass in winter. Admittedly, low-E will diminish slightly the amount of solar gain in winter but our AGS system is the principal heat source and gain through the windows will be welcome but not essential.

That said, we may leave off the second level overhangs for the first one or two years.  It will probably take that long for the AGS system to charge the thermal mass with enough heat for a year-round constant floating temperature at a comfortable level.  Accepting some summer solar gain to augment the output from the solar collector might be a good strategy.

Also, after the AGS system reaches equilibrium, we will assess the need for thermal window shades for nighttime and gray day use.  If the system provides plenty of heat, they would be superfluous, if not, they can be added.  Their function would be to keep moving air (convection) away from the glass and thereby slow conductive heat loss through the glass.  Secondarily, less convection would make for a more comfortable living environment.  In order to be successful, the shades would need to be sealed as tightly as possible on all four edges.  Heavy drapes, regular window shades or louvered blinds help some but are not the same thing and, in some cases, actually enhance convection.

Construction - Recap of the dirt and concrete phase from a DIY perspective

Naivety or Is It Perpetual Optimism?
Wow, I had no idea of the amount of time and effort that would lead up to building actually with wood.  As of early winter 2015, we have done dirt and concrete work for 15 months. I've been guilty of saying that, by the time we are ready to build with wood, the house will be half done!

Even after having roughed out the excavation into the side of the hill myself, it was hard to

Excavation roughed in (click on photo to enlarge it)

imagine the amount of heavy labor and machine time that would be required to build and install the French drains, to build and install the collector and conduits for the AGS system, to form and pour footings, to pour foundation walls, to backfill and compact it, to build retaining walls and do the landscaping necessary to control erosion while the house was being built. 

Lack of Experience
While I feel reasonably qualified to do carpentry, electric, plumbing, tile-setting, etc., I overestimated my ability to crash-course the dirt and concrete work.  It took very little time with the pros (that we reluctantly hired) to feel intimidated by their practical knowledge -- the kind that is indiscernible by reading or web-searching.  My early posts on this phase of the construction are testimony to my naivety.  If I had tried to follow through with those plans so confidently projected then, I would have burned significant time and money and had a compromised outcome.

Excavation
As our excavation contractor operated the backhoe, I was usually handling the measuring

Real professional at work

rod for the rotating laser that guided his movements.  It is amazing the level of skill it took for him to stay within the tolerances of an inch or two, whether it was at the bottom of a trench or on the grade that under-girds the future slab floor.  

With the proper equipment he could provide and operate (as opposed to my over-doing with a track loader as I originally imagined), the French drains and the AGS conduits were installed with minimal disturbance of the soil on which the house will rest.   This is a huge advantage with our wind-blown loess soil which, when undisturbed, provides excellent support for a concrete slab even without the obligatory intervening layer of rock.

Concrete Work -- The Wide Footing
The footing under the concrete walls required 37 yards of concrete poured from a

Wide footing pour

conveyor truck.   As a DIYer, would I have been able to order the right amount of concrete and handle the conveyor after having never seen one before?  Maybe on the first account but not so likely on the second after seeing it done.  Would I have known to monitor the height of the pour with a laser instead of screeding off of the form?  No.

Concrete Work -- The Wall
For the week or so it took the contractor to set the forms, pour 36 yards of concrete and dismantle

Wall pour

the forms for the concrete wall, I was mostly a spectator.  At the end of the day, I was exhausted from merely watching the huge amount of physical effort that the process takes. For instance, 118  2' x 8' individual forms, weighing close to 100 lb a piece, had to be carried to the wall site, stood up and fastened to place. When the wall was poured using a pump truck, several hearty guys stood on top of the forms and teased the air out of the concrete by pumping 2 by 2s up and down to a depth of 8 or 10' at a time for the biggest part of an hour. And dismantling, carrying and stacking the forms and loading them for transport was no less arduous than setting them up for the pour.   Makes me wonder about the average life expectancy of concrete workers. 

Concrete Work -- The Narrow Footing and the Foundation Walls
Even though it was time-consuming, the narrow footing for the insulated concrete walls

Homemade forms for the narrow footing

was easily manageable for a DIYer with handy friends and family -- both the forms and the pouring.  Using wood for the forms was old fashion but I had the wood so the forms were free except for a few bucks to my friend who helped install them.

The insulated concrete form foundation wall is also easily within the reach of a DIYer  with regard to setting of the forms and pouring them.  Setting up the ICFs is straightforward if one follows the installation guide that the ICF manufacturer provides.

Slab-On-Grade Concrete Floor
Managing the rock sub-base under the slab was mostly a matter of providing guidance

Floor pour

for the slinger-truck operator, viz., setting the grade pins and marking off the grade beams and piers . There was only a little tweaking for us to do with garden rakes and flat shovels after the truck had left.

When it came to pouring the floor, all I could do was watch while just under 1,700 sq ft of concrete was poured at one time.  If I had done it, it would have been in small increments so as to be able to use the previous increments(s) to screed off of, thereby necessitating perhaps as many as 8 separate pours.  And I would not have been able to have achieved the same quality of surface finish that the professionals did. 

Bottom Line
Despite not having budgeted for it ahead of time, the money spent for professional help was a good investment, especially since it allowed us to beat the winter weather and save several months building time.  Now it behooves me to find ways during the rest of the construction to recoup some of the outlay for professional help.

Construction - Insulation/Watershed Umbrella for the Annualized GeoSolar System - Cont'd

The first post on the insulation/watershed umbrella delt with its configuration as described by John Hiat in his self-published book, "Passive Annual Heat Storage; Improving the Design of Earth Shelters".  This post is an attempt to explain why the umbrella is so essential for the function of the AGS system.  The "Annualized GeoSolar" terminology, by the way, is taken from a paper by Don Stephens that complements and advances Hiat's original design; the "insulation/watershed umbrella" terminology comes from Hiat.  A thorough discussion of the AGS system is found in three earlier posts:   first post, second post, third post.  The umbrella is covered in the third post.

The Function of the Umbrella As Part of the AGS System

The insulation/watershed umbrella increases the size of the thermal mass that is heated passively by the summer sun via the solar collector and the nine conduits running beneath the floor.  Without the umbrella, the thermal mass would consist of only the concrete floor, the rock sub-base and that part of the underlying soil that remained dry.  The concrete earth contact walls would also contribute but not the earth behind them because they would have to be insulated.  The thermal mass would still be considerable because our ranch house is spread out so much. But, even so, why take a chance on the solar collector not being able to keep up with the heat loss from the mass during the cold months?  Better to risk an overheating problem than an under-performing system.

Heat will be lost from the house mostly in four ways:  (a) the envelope of the house will be the main source of heat loss irrespective of how tight or insulated it is, (b) some heat will be lost directly from the thermal mass outward through the insulated foundation above the umbrella and (c) some heat will be lost through the energy recovery ventilator that uses fresh outside air, even in winter, for indoor air quality. The heat losses through the envelope and ERV will be made up by heat moving out of the thermal mass into the house.  The heat losses through and under the foundation are simply lost until recharged by the solar collector during next warm weather season,

Late Winter Blues
However, there will come a time at the end of winter when the heat that is readily available from the top layers of the mass has been used up and heat from lower down may not migrate fast enough to the surface to keep up with the heat loss through the envelope, foundation and ERV.  In which case, the ambient indoor temperature may drop a few degrees until Spring when the average outside temperature rises above that of the house at a time when the solar collector has already begun to reheat the thermal mass.  So it's all about getting enough heat into the thermal mass before the cold season then miserly keeping it there to compensate for heat losses from the house as long as possible in order to minimize a chillier indoor temperature in late winter and wait out the recharging of the solar collector in the spring.

The rate at which heat leaves the mass during the winter will be slowed somewhat by heat gain through the south-facing windows as well as heat generated by living in the house -- cooking, lighting, human bodies and hot water use.  Both Stephens and Hiat have already warned that the ambient temperature will be lower for the first couple of years until the input from the solar collector is capable of hitting our target of 74 degrees year-round.  At that point, it remains to be seen just how much the temperature drops in late winter/early spring, if any.

How Does It Work?

Heat seeks cold so the exterior winter environment is a prime target for the heat in the house and in the thermal mass.  Heat loss from the house is covered in other posts while heat loss from the mass is our focus here.  It exits the periphery of the mass in the winter as high up as possible.  In our case, the insulated concrete foundation and umbrella-insulated footing force most of the escaping heat to pass under the footing.  With our insulated concrete wall and without an umbrella, the top of the footing would be the departure point for the heat. With the umbrella, the departure point moves laterally to the outer edge of the umbrella.

According to Hiat, it takes 6 months for a unit of heat to travel through 20 feet of dry earth. Once the outside average temperature is lower than that of the thermal mass, heat loss begins.  The first sketch shows what happens with an umbrella in place. The dashed and dotted lines represent the interface between warm and cold earth. Dashed line "A" depicts

Click on image to enlarge for viewing.

the maximum of heat storage possible at the end of the warm weather season.  If the umbrella is 20' wide as Hiat suggests, the dashed line "a" represents the maximum of amount of heat that could be lost in 6 months. Notice that the umbrella virtually eliminates any heat loss from under the house, assuming that the insulation in the umbrella stops all heat loss.  In reality, its R-factor is sufficient to stop enough loss to keep that part of the floor nearest the wall much warmer than it would be without it.

At one point, in order to save a few dollars and a little effort, I toyed with the idea of making the umbrella 16' wide and it wasn't until I sketched out the two options and realized how much heat would be lost from under the house did I forget about the narrower umbrella. Even if the ranch style footprint would still provide enough thermal mass to compensate for the additional heat loss, the floor next to the exterior walls would probably be uncomfortably chilly towards the end of the heating season.

The second sketch shows the maximum amount of heat loss without the umbrella ("C" would be the maximum of heat available and "c" would be the maximum of heat lost in 6 months).  The +/-20 foot floor expanse between the two dotted lines would undoubtedly be uncomfortable and more so the closer you come to the outside wall.

Role of the French Drains
The French drains are 10' below the floor and essentially limit the vertical dimension of the thermal mass to 10" which should be more than adequate for AGS system. Heat migrating into the living space from any deeper would not be very helpful because it would barely make it through the floor before the cold weather season was over.  If the water table were to rise to the level we know it can (by monitoring piezometers for several years before beginning construction), it would bleed heat away from thermal mass. The drains make sure that it stays at the harmless level of 10" below the floor.  For more on the French drains, go to first post, second post and third post detailing the design, fabrication and installation of the drains.

2 - 3 Year Time Delay
The umbrella largely solves the problem of conserving as much heat as possible within the thermal mass.  The remaining question is whether our design for the solar collector/conduits will pump enough heat into the thermal mass to fill it out to the maximum.  According to both Hiat and Stephens, one should expect it to take 2 - 3 years to max out.  Afterwards, Stephen says, the problem could be too much heat such that some of the system would need to be mothballed.  In order to speed things up, we may wait a couple of years to install the sun shades over the south-facing second story windows so that the summer solar gain will go into the thermal mass and augment the solar collector heat.  And, if push comes to shove, we may install infrared heaters as supplemental heating for the first couple of winters, particularly if the code requires some sort of thermostatically-controlled heat.

Earth Contact North Wall
The foregoing discussion does not take into account the north wall.  Without the umbrella next to it, it would have to be insulated on both sides for all or nearly all of it height.  By moving most of the vertical insulation horizontally into the umbrella, only the top three feet or so need to be insulated vertically, viz., that part exposed above the grade, that part next to the topsoil covering the umbrella then a foot or so below the umbrella.  And, by reorienting the insulation, most of the two-story wall and the earth behind it creates so much thermal mass as to make an earth sheltered roof discretionary or unnecessary.

Incidental Heat from Other Sources
Heat during the cold months will be lost principally through the envelope of the house, especially through the windows, and through the energy recovery ventilator as it exchanges +/-30% of the indoor air every hour. Most of the replacement heat will migrate out of the thermal mass but there will be incidental heat from other sources as well. Most will come from sunshine through the south-facing windows.  But human body heat, heat from lighting (which we hope to minimize with LED), cooking heat and heat lost from hot water during bathing will also contribute. And, as mentioned above, we may invite the summer sun in through the second story windows for a year or two.

Cooling Season
The function of the AGS system during the cooling season is pretty simple.  Our goal is to maintain a year-round floating temperature in the low 70s, expecting it to rise above the average floating temperature a couple of degrees by the end of the cooling season and fall a couple of degrees by the end of the heating season.  Heat seeks cold so, at these temperatures, any summer heat penetrating the envelope will go immediately into the thermal mass without altering the ambient temperature, or at least not until the last weeks of the cooling season when the cumulative amount of heat uptake is more than the top layers of the thermal mass can absorb and distribute at the 20' per half-year rate.  Heat gain through the envelope will not come through the windows.  The windows will be shaded by overhangs that block the summer sun but admit the winter sun.  The exception could be the delay of overhangs for the second story windows as mentioned above.

The Rest of the Story
At the time of this writing in early winter, I had excavated for the umbrella without knowing for sure when actual installation could begin due to the weather.  The excavation was a matter of removing enough soil to allow the bottom of the umbrella to rest on the footings and slope downhill -- about two feet of soil had to be removed.  

By going ahead with the excavation when the likelihood of installing the umbrella yet this

Insulation protecting the footings under the foundation walls

year was pretty remote, the footings were a little more exposed.  So I purchased 2" thick expanded polystyrene sheets, sawed them in half lengthwise, laid them over the footings and weighted them down with stones.  Eventually, the insulation will be recycled as vertical insulation on both sides of the concrete garage walls.

Hang on, additional posts on the umbrella will follow as it is installed after the spring rainy season.

Construction - Damp-proofing the Earth Contact Wall

Is Damp-proofing or Water-proofing Really Necessary?
Yes and No.  "Yes" because the building code requires it.  But perhaps "No" from the standpoint of needing it long term.

The probability of the earth contact wall getting wet from surface runoff is low. The insulation/watershed umbrella will extend northward from the wall for 20' and the backfill behind the wall will be sloped away from the wall in three directions and end in swales to direct the water around the house and northward to a wet-weather creek at the north edge of the property.

The probability of the wall getting wet from a rising water table is non-existent due to the elaborate French drain system we installed 10' below floor level to lower the water table 
(first post on the French drains, second post on the French drains and third post on the French drains).

Is a Footing French Drain Really Necessary?
Yes and No.  "Yes" because the code requires it and because it may have some advantages until the backfilling is complete and the umbrella is in place.  "No" is probably the correct answer for the long-term because the chances of water reaching the bottom of the wall will be slim and none except perhaps near the ends of the wall. And the bottom of the wall is 7" below the floor level and the footing drain is below the top of the footing, making it a foot or more below floor level.

Ideally, the backfilling should be done in shallow lifts (layers) and each lift compacted.  My intention is to let nature do the compacting while I finish the house. Now that the wall is damp-proofed, I plan to backfill to a depth equal to about half of the final height of the backfill, or 5 or 6 feet, then let it compact itself over time. Eventually, the backfilling will be carried to completion and the umbrella installed.  In the short-term, the footing drain will be useful for draining any water soaking down through the initial lift so as to eliminate hydraulic pressure against the back of the wall.

Rather than encompass the fabric-covered drain with rock, I used sand that not only enveloped the drain but also was several inches deep on top of the footing so as to provide a passageway for water from the wall to the drain under the backfill.

Choosing a Damp-proofer
The fact that water at the wall will not a problem made it tempting to go with an unsophisticated material such as an asphalt based non-fibered roof and foundation coating at 11 cents per square foot.  My concrete supplier however recommended the Platon Waterproofing System at 22 cents per square foot.  The 11 cent differential amounted to $124 to cover 1,128 sq ft which seemed by far to be the best value.

Overview of the damp-proofing membrane; notice the sand
bridging from the membrane to the footing drain (click
on photo to enlarge for detail)

In order for the asphaltic coating to cover well, some areas of the wall would have required parging to cover up surface porosity in the concrete.  Some of the wall also would have had to have been power-washed to provide a reliable bonding surface. And I was not too keen on working with an asphaltic material.  With the Platon system, there is no need to "water-proof" the wall; it provides a drainage plane between the membrane and the wall so that water drains immediately to the French drain instead of going through the wall. And it could be hung without regard to the condition of the wall in less time than it would take to coat the wall, much less parge and wash it.  So, coughing up an extra $124 with the promise of less hassle, made the choice of the membrane a no-brainer.

Installing the Drainage Plane Sheets
Spoiler alert:  Despite researching the installation of the membrane, I misunderstood which side faces the wall only to find out when it was too late that we had installed it backwards.  Fortunately, the side facing the wall was sufficiently irregular as to facilitate drainage.  This is written after living in the house for nearly three years without seeing any water leakage, thanks in part perhaps to the insulation/watershed umbrella overlaying it.

The deadmen divided the membrane into four linear sections. We cut

The washers (left), removed from housewrap nails (top),
were mated with the recycled Tapcon screws (right) to
fasten the top of the membrane

each section to fit then stood it on the footing while fastening. We wrapped the material around the corners onto the deadmen for 9" or so. We used Tapcon screws to fasten the top of the membrane to the wall after mating the screws with the orange washers from housewrap nails. The manufacturer sells an attachment system but the Tapcon screws and washers worked fine at nominal cost, especially since we salvaged the screws from the wood braces that we had used for the insulated concrete forms. The membrane would have been unmanageable working alone so I was happy to have help from stepson, Keith.

Where the membrane got shorter as it

Close-up of the membrane; connecting the dimples on the
wall side are vertical channels to shunt water downward

approached the ends of the wall, the sections were laid flat for cutting.  We also pre-cut the membrane for the top 4' of the 12' high section of the wall and stored it until, several months down the road, the backfilling reaches that level.  It can then be installed while standing on the initial backfill instead of on ladders. At that time, it will be shingled under the lower section (not over as with roof shingles) which means the screws holding the lower section will have to be removed, the upper section tucked in behind it and the screws replaced.  Shingling under means that the edge of the lower section is has to be attached firmly so that it is not pried loose by soil when the backfill is done.

Construction - Concrete Work - Slinging the Gravel Sub-base and Pouring the Slab Floor

This is the sixth and final post on the concrete phase of construction (of the living quarters of the house). The slab floors for the garage and the screened porch will follow eventually. (Click on any photo to enlarge it for detail.)

Preparing for the Gravel Sub-base
The plumbing rough-in bunched the conduits together so tightly, especially those going to the bathrooms, that air space existed under them and any downward pressure on many caused them to flex.  Since the 3/4" clean gravel of the sub-base would not find its way

Ready for the gravel sub-base; the conduits and
waste water pipes have been packed with sand, the
grade beams and piers have been marked with paint
and the grade stakes are in place; black plastic covers
the PEX tubing to protect against ultraviolet radiation
for several months until the roof is in place

under and between most of the conduits, the concrete floor would not be properly supported.  In order to remedy the situation, I hand-packed, as much as possible, sand into

the air spaces and left extra sand on top of the conduits.  As much as I hated to see rain a few months ago, I eagerly awaited a downpour to compact the sand and carry the extra into the crevices below and between the conduits.  Mother Nature could not have been more cooperative -- no sooner than step-son Keith, handyman Pat and I finished distributing the sand, she dumped 3/4" of rain overnight that seemed to do the job just fine.

Under load-bearing walls and posts, the thickness of the slab had to be doubled in order

A wooden form blocks off for the bathtub drain; marking
paint delineates a grade beam on the left and a pier
adjacent to the wood form; tall grade stake in the fore-
ground, shorter spikes mark the corners of the grade
beams and a pier

to form grade beams and piers.  These were laid out and delineated first with 6" outdoor spikes driven into the soil then with marking paint on the surface of the soil.  In order to preserve access for connecting the drain to the tub eventually, the area under the bathtub drain had to be blocked out.  A circumscribed, tall wooden form was securely anchored in place to block out the gravel and the concrete.

Finally, the operator of the slinger truck needed reference points for spreading an even thickness of gravel at the proper depth.  Accordingly, grade stakes in the form of 12" spikes were pushed into the soil to form a grid that more or less positioned them 15' apart.  The rotating laser and a hammer was used to position the tops of the spikes at the +/-5" fill level for the gravel.  The spikes were then sprayed with marking paint to give them visibility.   The spikes that delineated the grade beams and piers were driven much deeper so as not to be confused with the grade stakes.

Slinging the Gravel

It took four truckloads of gravel and a long half-day to sling the gravel into place.

The slinger truck in action

The driver/operator skillfully laid down an even layer without getting much more than a sprinkling in the grade beam and pier areas.  Three of us with garden rakes cleaned out the grade beam and pier areas and finished leveling and smoothing the rest of the gravel.


Compacting the  Gravel Sub-base?
Our plans called for 5+" of 3/4" clean gravel under the concrete.  Apparently, usual protocol calls for pouring concrete over the the slung gravel without compacting it first.  Our

Compacted gravel sub-base; burlap covers the black
plastic over the PEX tubing to protect it from wind damage

undisturbed soil under the gravel was more than dense enough to have supported the concrete without the gravel so it made no sense to top it off with gravel that was not compacted.  And the slinger truck driver confirmed our conviction by saying that the amount of shrinkage that could be expected from compaction would be 3/4".   I immediately had him top off the original layer with another 1" of gravel to give a finagle factor for compaction . Thank goodness there was a plate compactor in the family and it immediately saw some serious use.

Pre-pour Tasks
The designated pour day was too windy due to an approaching cold front and had to be postponed for a couple of days in the span of which rain was forecast.  In order to keep the soil dry for the concrete trucks, we spread 6 mil plastic sheeting and weighted it down with enough junk to withstand the stiff winds . Unfortunately, the effort proved fruitless because the rain was minimal. 

Two of Jamie Schulte's crew appeared the day before the pour and used a laser to snap chalk lines on the concrete wall and set grade pins designating the height of the pour.  As soon as Jamie and his crew had unloaded their equipment on the day of the pour, they used the plastic sheeting to fit a

The inaccessible areas were poured using a conveyor
truck; the accessible areas were poured directly from
the chute; notice the plastic moisture barrier in place

moisture barrier over the entire gravel sub-base.  There were three floor drains that also needed to be suspended at the correct height over the roughed-in PVC pipes.  By using metal drains for two of them, I was able to drill, tap and insert three set-screws in each one for securing them to the PVC.  For the shower stall, it was only necessary to wrap foam around the PVC as a space holder for the brass drain to be installed later.

Pouring the Floor
The depth of pour was targeted to be 5" and level with the top of the foundation wall. The square footage was 1,680.  In lieu of metal reinforcing mesh, the mix was

Beginning the final finish 6 hours after beginning the pour

strengthened by the addition of fiberglass fibers and using 8 bags of cement per yard of concrete for a crushing strength 5,000 psi.  Some of the concrete was poured from a conveyor truck, the rest directly from the chutes on regular ready-mix trucks. The amount of concrete needed -- 29 cubic yards -- surprised even Jamie.  The considerable square footage of grade beams and piers, which double the thickness of the concrete, was probably the major reason for underestimating the volume.  In any case, the cost of the concrete, along with the surcharge for the conveyor truck, was about double what I estimated originally.

Wrapping Up the Floor
Concrete shrinks as it sets, causing random cracks.  Control joints are used in an attempt to direct the cracks to where they will be least problematic.  They are sawed into the concrete to a depth of about 1/4 of the floor thickness after the the concrete has had time to set but before cracking.  Jamie and a helper snapped chalk lines and used both a walk-behind and portable concrete saw to make the cuts.  Fortunately, we were able to hide most of the control joints under future partitions and a couple could be partially hidden under the future stairway and kitchen island.  Since it will be quite a while before the finished floor goes in, I am hoping all the cracking will have occurred, whether in the control joints or not, and the ceramic or porcelain floor tile will hide them without the crack expanding more later and cracking the tile.

The pour was done in mid-November and would be susceptible to cold weather damage if not protected.  Accordingly, Jamie recommended a product called "Cure & Seal" as a temporary coating lasting about three months before letting loose, which will get us through the winter, and one that does not compromise the bond of the thin set to the concrete when the tile is laid.  I tried applying it with a cheap garden sprayer but found it faster and easier to roll it on.  Five gallons cost $120 and was only a tad more than we needed for 1,680 sq ft.

Insulated Slab Edge
A final note.  The advantage of pouring the floor flush with the tops of the insulated concrete forms is that the slab edge is separated from the exterior environment by 5" of expanded polystyrene insulation.  Without the slab edge insulation, heat would be conducted in and out through the exposed concrete (thermal bridging) and alter the floor temperature adjacent the wall accordingly.  All energy certification programs require slab edge insulation (see first post on certification and second post on certification  (the latter is more germane to slab edge insulation)).