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House Specifications
Summary: The house is 16-sided, post and beam frame, and has two independent cordwood walls with foam insulation between the wall units. The mortar used to construct the cordwood walls is comprised of an experimental mix of paper, sand and masonry cement. The house is built on a rubble-trench foundation, reducing the amount of concrete typically required for a frost wall. The primary water source for the house is a underground rainwater cistern with a conventional well as a backup source in times of drought. The house is heated using passive and active solar, wood stove and electric boiler (off peak rate) as a backup. Electricity is supplied from the local utility and a grid-intertie, 4.2kW solar electric system.

Detailed Specifications:

Location: SE Minnesota, ~15 miles SW of La Crosse, WI
Number of sides:
16 sides, 2-story
Wall Thickness: 24”, (2) 8" cordwood walls with foam insulation in between wall units.
Outside Diameter (Corner to Corner): 41’6”
Inside Diameter (Corner to Corner): 37’6”
Approximate Living Space: 1,560 sq. ft. (1,000 sq. ft. 1st floor, 560 sq. ft. 2nd floor)
Roof: 16 sides, standing seam metal roof, 4/12 pitch, and 3’ overhang
Roof Trusses: 32 half trusses (2 sizes, 16 of each), 1’ energy heel
Foundation: Rubble Trench (5’ deep, 3’ wide, 43’ diameter)

Outer Cordwood Wall Specs (Approximate Figures):
-32 walls, 8’(h) x 8’(w)
-6,327 Blocks of 8” wood
-2,400 lbs. of dry newspaper
-19,586 lbs. of sand
-555 batches of mortar

18” of blown cellulose, ~R60
Cordwood Walls: R-36:5”-6”of Demilec Sealection 500 open cell foam@ ~R-20 + (2) 8” cordwood walls@~R-8 each
Footings: Dow 1” Blue rigid foam board, R5
Floor: Owens Corning 2” Pink rigid foam board, R10

Links to Journal Entries of Interest:

Rubble Trench Foundation: Excavation, Installation Part I, Installation Part II
Footings: Part I, Part II, Part III
Framing: Part I, Part II, Part III, Part IV, Part V, Part VI, Part VII
Trusses: Part I, Part II
Standing Seam Roof: Part I, Part II
Floor Plan: Electric, Walls, Etc.
Windows: Decision Process, Specs.
Cordwood Walls: First Wall, Second and Third Walls
Rainwater Collection System: Diagram, Cistern Installation


Heating Specifications

Summary: The house is heated by three different methods: solar, wood and electric. On sunny days during the winter, the bulk of the heating needs are supplied by both passive and active solar heating systems. Passive solar is provided by the sunlight that streams into the south-facing windows. These windows are strategically placed in the wall unit to provide ample sunshine in the winter months while 3' overhangs shade the sun in the summer.

The active solar heating system heats an insulated sand bed located beneath the floor of the house. It approximately takes 12 hours for the heat to travel through the sand bed into the floor.

Unfortunately the sun doesn't always shine—especially during the months of November and December. During cloudy periods, the house is heated by a wood burning soapstone stove. As backup, an electric boiler is used to supply radiant floor heat in the event that no one is present to stoke the stove. The electric boiler is tied to the local utility's off-peak rate program.

Detailed Specifications:

Active Solar Heating System:
(10) 4’ x 10’ solar collectors (used)
Circulators (Pumps): (2), 24v, 75 watt school bus heater pumps powered by (2) 75W, Siemens PV panels
Sand Bed: 8’ wide, donut shaped trench, 2’ in depth, lined with foam board ~R20
Heating Elements: (4) loops, ¾” Durapex tubing, 250’ each loop
Approximate number of pipe connections: 329 (none under the floor)

Passive Solar Heating System:
(10) 4’ x 6’, Double pane windows, located on the SE, S and SW sides of the house, 3’ overhang (both floors) for summer shading.

Wood Stove
Manufacturer/Model: Hearthstone, Phoenix Stove – EPA Rated
Btu/hr: 60,000
Burn Time:
Up to 8 hours
Heat Life:
Up to 12 hours
EPA Rating:
2.4 grams per hour

Electric Boiler: (2) 4.5kW elements, ~30,000 Btu/hr.

Domestic Hot Water: 80 gallon solar storage tank, Aquastar 125S

Links to Journal Entries of Interest:

Active Solar Heating: Sand bed Part I, Sand bed Part II, Collectors Part I, Frames, System Diagrams
Passive Solar Heating: Decision Process, Specs.
Wood Stove: Comparison

Boiler: Gas vs. Electric
Tankless Water Heater: Aquastar 125S Installation

Solar Domestic Hot Water System: Solar Heat Exchanger


Solar Electric Specifications

Summary: Electricity is supplied to the house by both electric utility and by a solar electric, grid-intertie system. The solar electric system while in operation supplies the house with over 3kW/hr of power. Any surplus is sold back to the local utility. During times when the sun isn't shining, power is supplied by the local utility.

Our solar electric system has been in operation since June of 2004 and if estimations prove correct, will provide enough power on an annual basis to meet our annual electrical demand. Updates will be given periodically on the Day Creek Journal as to the status of our net-zero goal.

Detailed Specifications:

System type: Batteryless, grid-tied PV system
Solar resource: 4.5 average daily peak sun hours
Production: 400 AC KWH per month average
Utility electricity offset: 100 percent estimated

24 Kyocera KC158G, 158 W STC, 23.2 VDC and four Shell SR100, 100 W STC, 17.7 V mp
Array: Eight, three-module series strings (K158Gs), and one, four-module series string (SR100s); 4,200 W STC total, 70 V mp
Array combiner box: Built-in Xantrex SunTie with 20 A fuses
Array disconnect: Built-in Xantrex SunTie, 100 A breaker and 1 A GFI
Array installation: Custom ground mounts, 40-degree tilt angle

Balance of System
Two Xantrex ST2500 XR-UPG, 120 VDC maximum input voltage, 44–85 VDC MPPT window, 240 VAC output
System performance metering: Two-channel utility KWH meter, Solar Guppy PC software to monitor inverter performance


Links to Journal Entries of Interest:

Frame Construction: Breaking Ground , Racks
Misc: System Efficiency, System Up and Running

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