Integrating Net-Zero Energy 

and High-Performance Green 

Building Technologies into 

Contemporary Housing in a 

Cold Climate 

Martin Yoklic

Mark Knaebe

Karen Martinson

United States

Department of

Agriculture

Forest Service

Forest

Products

Laboratory

General

Technical

Report

FPL–GTR–193
August 2010

Yoklic, Martin; Knaebe, Mark; Martinson, Karen. 2010. Integrating 

net-zero energy and high-performance green building technologies into 

contemporary housing in a cold climates. General Technical Report FPLGTR-193. Madison, WI: U.S. Department of Agriculture, Forest Service, 

Forest Products Laboratory. 13 p.

A limited number of free copies of this publication are available to the 

public from the Forest Products Laboratory, One Gifford Pinchot Drive, 

Madison, WI 53726–2398. This publication is also available online at 

www.fpl.fs.fed.us. Laboratory publications are sent to hundreds of libraries 

in the United States and elsewhere.

The Forest Products Laboratory is maintained in cooperation with the 

University of Wisconsin. 

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and does not imply endorsement by the United States Department of 

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and employer.

Abstract

The objectives of this research project are (1) to show how 

the sustainable resources of forest biomass, solar energy, 

harvested rainwater, and small-diameter logs can be integrated to a system that provides most or all of the energy 

and water needs of a typical cold climate residential household, and (2) to effectively interpret the results and convey 

the sustainable potential to the public. This project validates 

that (1) the combination of the BioMax® wood-pellet 

energy system (5 kW peak) with grid interconnected solar 

energy via photovoltaics (4 kW) can provide the majority 

of the power needs for a residential unit in a cold climate; 

(2) rainwater can be stored in a 2,500-gallon cistern and 

reliably filtered and disinfected for potable use; (3) systems 

to product and save energy and water are safe and reliable; 

and (4) these technologies are available and work well in 

cold climates similar to the project’s location in Madison, 

Wisconsin, USA.

Keywords: integrated design, passive solar, active solar, 

rainwater harvesting, photovoltaic (PV)

Contents

Page

Introduction......................................................................... 1

Methodology....................................................................... 2

Research and Systems Evaluation ...................................... 2

 Energy ............................................................................. 3

 Water............................................................................... 3

 Wood ............................................................................... 4

Program and Design Development ..................................... 4

 Structural System and Assembly .................................... 4

 Building Performance ..................................................... 5

 Renewable Energy Systems............................................ 6

 Rainwater Harvesting and Management......................... 7

Discussion..........................................................................10

Conclusion ........................................................................12

Acknowledgments..............................................................12

References..........................................................................12

SI conversion factors

Inch–pound unit Conversion factor SI unit

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

gallons (gal) 0.003785 cubic meters (m3)

ton 907.18 kilograms (kg)

mile 1.609 kilometers (km)

Btu 0.0002929 kilowatt-hour (kWh)
Integrating Net-Zero Energy and HighPerformance Green Building Technologies 

into Contemporary Housing in a Cold 

Climate

Martin Yoklic, Associate Research Scientist 

Environmental Research Laboratory, University of Arizona, Tucson, Arizona 

Mark Knaebe, Forest Products Technologist

Karen Martinson, Public Affairs Specialist

Forest Products Laboratory, Madison, Wisconsin

Introduction

In recent years, great strides have been made in improving 

the energy and water efficiency of housing. “Green” building improvements include the following:

•	 Water-conserving plumbing fixtures

•	 Higher efficiency heating and cooling systems

•	 Improved insulation and radiant control in windows

•	 Better building envelope design for insulation and moisture control

•	 Advances in renewable energy technologies for residential applications such as photovoltaics 

Acceptance and adoption of these technologies have been 

facilitated through incentives (public and utility) and regulatory mechanisms (building energy codes) resulting in more 

efficient buildings and lower costs compared with when 

green building improvements were first introduced. The 

energy challenges of recent years, combined with a better 

understanding of how human-produced greenhouse gases 

may be altering the climate, suggest that we need to do even 

more to reduce energy demand from traditional sources. 

The conservation and efficiency improvement gains that we 

have realized from advances in the building technologies 

listed are no longer enough. But, how do we raise the bar in 

energy- and water-use efficiency on the residential scale? 

Research in building energy modeling has shown that the 

cumulative energy performance improvements of individual 

building envelope components (high efficiency windows; 

better insulation in wall, ceiling, and foundation; and reduced infiltration rates and orientation) are greater than the 

sum of their individual impact. A synergy results from their 

integration.

Whereas conservation is critical and has provided important 

gains in energy and water efficiency, integrated systems are 

emerging that can make truly sustainable use of our natural 

resources. This project examines how renewable energy, 

rainwater harvesting, and the waste from forest thinning can 

be integrated for residential sustainability in cold climates 

and how energy and water-use reductions can be achieved.

Wood products made from small-diameter logs, harvested 

rainwater, the energy from wood waste, and the sun are all 

plentiful and renewable resources. The thesis of our research 

is that these resources, if effectively harvested and managed, 

are sufficient to provide a sustainable support system for 

cold-climate housing, reducing reliance on fossil resources 

(energy and groundwater), while making better use of forest resources. Products and technologies to harness and 

use these resources are available. However, putting them 

together requires an integrated approach to building design 

and engineering. This project is designed to demonstrate 

how currently available systems and strategies that use these 

resources can be integrated into contemporary housing and 

to test applications at the residential scale in order to validate system performance.

The Research Demonstration House was completed in 2001 

on the grounds of the Forest Products Laboratory (FPL) in 

Madison, Wisconsin. Its purpose is to showcase innovative 

new wood products and wood composites, such as Southern 

Pine flooring and wood composite shingles; demonstrate 

and evaluate innovative wood products applications and 

durability (as evidenced by the wood floor and walls in the 

basement); and to study moisture migration through walls. 

This applied research program was expanded starting in 

2003 to include investigating residential rainwater utilization and renewable energy applications.

For this research, a building (coined the Carriage House 

by Mark Knaebe) the scale of a contemporary double car 

garage or workshop (Fig. 1) has been designed and constructed adjacent to the Research Demonstration House to 

contain the potable rainwater and renewable energy systems. 

The project also showcases advanced construction methods 

using small-diameter lumber products. A primary objective 

is to introduce and build acceptance of these sustainable 

products and show how they can be integrated into the contemporary housing market.

Together the Research Demonstration House and the 

Carriage House typify a house in the suburban upper Midwest of the United States. By combining state-of-the-art 
General Technical Report FPL–GTR–193

2

renewable energy technologies and innovative rainwater 

harvesting systems, the research assesses whether net-zero 

energy and optimal rainwater use is achievable in a cold climate. The cost, efficacy, and reliability of these systems are 

being evaluated while their potential is demonstrated.

The primary question addressed by this applied research 

program is whether contemporary building technologies and 

systems can be effectively integrated to accomplish a much 

higher level of residential energy and water efficiency in 

a cold climate similar to that of Madison, Wisconsin. The 

energy and water efficiency targets for this research evolved 

through our analysis of efficiency improvement opportunities associated with the wood products from the Research 

Demonstration House, conditions of the project site, and 

through discussions about complementary ongoing FPL 

research programs. The project’s energy performance target 

was modeled after those being developed and promoted by 

the Department of Energy’s Energy Efficiency and Renewable Energy Program (DOE 2010). 

The water efficiency goal was developed through ongoing research by the author based on work conducted in the 

southwestern United States. The use of renewable wood 

products came out of research conducted by FPL on the 

potential for small-diameter lumber products from fire-wise 

forest thinning. These targets were reaffirmed in the October 2008 report from the National Science and Technology 

Council Subcommittee on Building Technology Research 

and Development (NSTC 2008), which shows that designs 

of new buildings and retrofits of existing buildings over 

their life cycle accomplish the following:

•	 Produce as much energy as they consume (net-zero energy) and significantly reduce greenhouse gases.

•	 Double the service life of building materials, products 

and systems, and minimize life-cycle effects.

•	 Halve the use of domestic water (to 50 gallons per day 

per person or less), maximize water recycling and rainwater harvesting, and minimize storm water runoff.

•	 Achieve breakthrough improvements in indoor occupant 

health, productivity, and comfort.

Through the FPL Advanced Housing Research Center’s 

cooperative effort with the University of Arizona’s Environmental Research Laboratory, this project was developed 

to examine how using an integrated design approach that 

incorporates energy efficiency, renewable energy, harvested 

rainwater, and the waste from forest thinnings can improve 

residential sustainability in cold climates.

Methodology

This project used an iterative research, programming, design, and development model to integrate renewable energy 

production, rainwater harvesting, and new advances in wood 

product utilization into the FPL Research Demonstration 

House. Initial research in water and energy use requirements 

for a typical energy-efficient residence in Madison were 

gleaned from the literature and usage assessments from local utilities for both energy and water. Renewable energy 

technology and rainwater harvesting systems options were 

evaluated to determine the most strategic approach toward 

the project goal of net-zero energy use and a 50% reduction 

of potable water use for an existing single family residence 

in a cold climate. The results of these investigations were 

used to develop a design program appropriate for the house 

and site in function, performance, aesthetics, interpretive 

potential, and associated FPL research.

Design development and engineering of the systems proceeded from the results of the research and systems evaluation phase. Through a series of design iteration and review 

meetings with FPL researchers, we determined the scope 

and scale of the project and prepared design development 

documents.

To effectively address ongoing systems integration details, 

funding, and the weather, we used a design-build approach 

to construction. The design-build process allowed for innovative problem solving to occur during construction. This 

approach also allowed for the data monitoring and controls 

associated with ongoing research to evolve and be integrated into the building.

Research and Systems Evaluation

This research program, initially focused on rainwater harvesting opportunities at the FPL house, evolved into a more 

comprehensive integrated look at residential sustainability in 

a cold climate. The physical design and ongoing research at 

the Research Demonstration House combined with the need 

for a space to house the BioMax®, a pilot-scale biomass 

system that converts biomass energy to thermal or electrical power, or both); a requirement for rainwater storage that 

would not freeze; and an opportunity to demonstrate the 

use of new wood products from forest thinnings led to the 

decision to develop another facility adjacent to the Research 

Figure 1. Carriage House south elevation.
Integrating Net-Zero Energy and High-Performance Green Building Technologies into Contemporary Housing in a Cold Climate

3

Demonstration House. The Carriage House provides a platform to address the broader residential sustainability issues 

in association with the Research Demonstration House without affecting ongoing research.

The expanded scope of the research program addresses energy, water, and better utilization of forest resources. In addition, new wood products, developed from material traditionally considered as waste, are being evaluated for integration.

Energy

To address the energy-use question and to create a benchmark for the Carriage House systems design and performance evaluation, we used electric and gas use formulas 

developed by Madison Gas and Electric (MG&E) based on 

data from their Good Cents certified homes program (personal communication with Robert K. Stoffs, Community 

Energy Manager at MG&E, May and June, 2009). Table 1 

shows estimated average annual energy use.

Natural gas is the primary source for residential heating 

and comprises about 75% of the annual average residential 

energy use. While coal-fired powers stations supply the 

majority of the electricity, MG&E has a strong commitment 

to renewable energy sources and energy efficiency (City of 

Madison 2008). 

Options for achieving net-zero energy at the residential scale 

include demand reduction and on-site electrical generation. 

Because the majority of the energy use in housing is for 

heating, building envelope improvements to decrease heat 

loss (better insulation and reduced infiltration) and passive 

or active solar thermal systems to improve heat gain in the 

building can be effective at reducing energy demand. These 

strategies were employed to optimize the thermal energy 

performance of the Carriage House. For the electricity use 

requirement, a number of renewable energy systems are 

available for onsite generation. The electric production systems evaluated include photovoltaics, wind power, hydrogen 

fuel cells (methane reformer), and biomass energy conversion systems.

Wind was insufficient at the site, and hydrogen fuel cells 

are an emerging technology that has potential and may be 

considered for later inclusion. Photovoltaic systems have 

become widely available and incentives for their application are readily available. Biomass systems for electric and 

heat energy production, while in the emerging technology 

category, are a sponsored research initiative of FPL. One 

such system, the BioMax®, was being evaluated by FPL and 

made available for inclusion into the project. The BioMax®

together with an appropriately sized photovoltaic system 

will be evaluated to assess their capacity to provide the electric power requirements of a typical energy-efficient house 

on a net annual production basis. 

Water

The residential sector accounts for 22% of the annual energy consumption in the United States. Average per capita 

water consumption exceeds 100 gallons per day nationally. 

Nationally, the daily indoor water use per capita is 69.3 gallons. Conservation measures such as installing low water 

use toilets, flow controls, and high-efficiency clothes 

and dishwashers can reduce water use by about 35% to 

45.3 gallons. See per capita daily water use in Table 2 

(AWWA 2009).

In the City of Madison, the residential average daily use 

per capita (indoor and outdoor) is about 73 gallons per day. 

For an average household of 2.5 persons, this is about 184 

gallons per day (City of Madison 2008). Residential water 

use (indoor and outdoor) in Madison is 25% less than the 

national average on a gallons per capita day (gpcd) basis 

(73 gpcd versus 100 gpcd nationally). This variance from 

the national average is due in part to the region’s rainfall 

frequency and total volume, offsetting demand for outdoor 

irrigation.

The use of harvested rainwater for toilets and clothes washing could net a 60% reduction in indoor use per capita from 

the municipal water supply. Managing on-site rainwater and 

using greywater for irrigation would further reduce municipal water use.

Table 1—Estimated average annual energy usea (typical 2,000 ft2 energyefficient house) 

Type Use Equationa

 Therms kWh kBtu kBtu/ft2

Natural gas Heating 0.20 × ft2 + 150 550 15,950 54,982 27

HW and cooking 360 10,440 35,988 18

Total 0.20 × ft2

 + 510 26,390 90,970 45

 

Electricity Cooling 0.40 × ft2 + 800 54 1,600 5,459 3

Plug loads 244 7,164 24,444 12

Total 1.06 × ft2 + 6,684 298 8,764 29,903 15 a

Because the Research Demonstration House is largely unoccupied, we used energy use data from 

MG&E that is representative of a typical residence in Madison, Wisconsin. The energy use values and 

equations shown in this chart are from research conducted by MG&E through their Good Cents Program. The breakdown between energy type and use show that 75% of the annual energy requirement for 

a typical house in Madison is for heating. The factors in the equations column are from MG&E. The 

energy values in shaded cells are conversion by author, unshaded by MG&E. 
4

General Technical Report FPL–GTR–193

Wood

New forest-management programs to remove excessive 

undergrowth and smaller trees (ladder fuels) have been 

initiated in response to the increasingly large and destructive forest fires. These programs generate a large volume 

of small-diameter logs, slash, and wood chips that have 

little or no value in the traditional timber industry. Product 

development research for these waste materials includes 

investigations on the use of wood chips as a fuel for electric 

generation, and initiatives to develop products from the 

small-diameter logs. One small-diameter log product is the 

direct use of the small-diameter logs for construction (FPL 

has sponsored a number of projects demonstrating the use 

of this material). Another higher value product, laminated 

tongue and groove decking, has been developed by a manufacturer in Northern Arizona. See sidebar below.

Small-Diameter Log Background

The frequency and devastation of large forest fires 

have necessitated changes in the management of forest resources in the United States. Essentially, forests 

are being cleared of smaller understory trees to prevent them from laddering fires to the larger trees. This 

new management strategy has increased the availability of small-diameter logs. Incentives for producing 

products made from small-diameter logs are needed, 

and FPL is leading in this market development effort. 

The Carriage House is a small part of this program and 

was designed to showcase the use of small-diameter 

logs and new small-diameter log products in the construction. Both wood waste energy generation and the 

use of small-diameter log materials are at a level of 

development suitable to be demonstrated and evaluated in this project. 

Program and Design Development

These new initiatives broadened the research agenda for the 

Research Demonstration House. Rainwater harvesting and 

management required a cistern for water storage, pressurization and filtration that was protected from freezing temperatures. A solar photovoltaic system required a south-facing 

rooftop, and the orientation and shading of the Research 

Demonstration House’s south roof was not optimal. In addition, an on-site, residential scale BioMax® being tested by

FPL was re-commissioned as a component of the renewable 

energy program for this project. To accommodate these a 

new building, the Carriage House, was required.

These program requirements, the cistern location, a southfacing roof for photovoltaics, and a space for the BioMax®

determined the size of the new building. The Carriage 

House was sited in response to the solar access requirements, infrastructure proximity, and contextual relationship 

to the Research Demonstration House. The Carriage House 

was designed with exterior detailing and roof line that was 

sympathetic with the Research Demonstration House, appearing as a detached double car garage. 

The following sections address (1) the integration of the 

small-diameter log structural system with contemporary 

construction, (2) the passive solar design and building 

thermal performance in response to cold-sensitive systems 

that will be housed in the space, (3) the renewable energy 

systems employed, and (4) the rainwater harvesting and 

management systems.

Structural System and Assembly

A reinforced concrete grade beam set on piers to prevent 

frost heaving forms the building foundation. A 2,500-gallon precast cistern is located under the floor of the Carriage 

House’s east bay. The structure is made from small-diameter 

log columns and trusses (peeled ponderosa pine). For winter 

space heating (frost protection), a sunspace was integrated 

into the south façade. Figure 2 depicts the building frame 

Table 2—Per capita daily water use (typical 

single family home, indoor only) 

Without

conservation 

measures 

With 

conservation 

measuresa

Use Gpcdb Percentage Gpcd Percentage

Shower 11.6 16.8 8.8 19.5 

Clothes washer 15.0 21.7 10.0 22.1 

Dishwasher 1.0 1.4 0.7 1.5 

Toilets 18.5 26.7 8.2 18.5 

Baths 1.2 1.7 1.2 2.7 

Leaks 9.5 13.7 4.0 8.8 

Faucets 10.9 15.7 10.8 23.9 

Other 1.6 2.2 1.6 3.4 

Total 69.3 45.3 

a

Water conservation measures can lower consumption by 35%. 

Using rainwater for clothes and toilets (shaded cells) nets a 

60% reduction in municipal water use. 

b

 Gallons per capita day.

Figure 2. On-site structural assembly of small-diameter 

logs and trusses.
during construction. The building cross section in Figure 3 

details the sunspace and location of the cistern. Between the 

perimeter log columns, the infill walls use traditional 2 by 4 

framing and insulation systems. The small-diameter log roof 

trusses are exposed on the interior and a laminated tongueand-groove decking also made from small-diameter logs 

forms the roof system (Fig. 4).

Construction Systems and Assemblies as Simulated

Foundation: Concrete grade beam on piers with 

1-1/2-in. rigid perimeter insulation (R7.5 ) vertical on 

the grade beam and 2 ft to the interior under the concrete paver flooring.

Structure: Small-diameter log 6-in. diameter posts 

and trusses with custom 1/4-in. steel plate connectors.

Walls: Wood–plastic composite siding, Tyvek building 

wrap, 2-in. Hunter H-Shield-NB rigid insulation with 

nailable sheathing (R9.1), 1/2-in. oriented strandboard 

(OSB) structural sheathing, 2 by 4 framing in between 

the structural posts with fiberglass batts (R-13), and 

1/2-in. gypsum board.

Steel Roof: 3-1/2-in. Hunter H-Shield-NB rigid insulation with nailable sheathing (R19.1), 1/2-in. OSB 

structural sheathing, 2 by 4 small-diameter log laminated tongue and groove decking.

Windows: Vinyl covered wood, fixed and operable; 

south windows (interior and exterior) have double 

pane clear glass, other windows have double pane 

low-E glass.

Building Performance

The Carriage House is an unoccupied space; however, the 

interior temperature does need to maintain temperatures 

above freezing because of the exposed rainwater disinfection system inside. To provide this frost protection passively, an air-fed solar collector referred to and modeled as 

a sunspace was incorporated into the south façade of the 

Carriage House. CALPAS3 hourly simulation software with 

the generic COLD.GMY weather file was used to assure the 

building would remain above freezing in winter (Berkeley 

Solar Group 1984). This program was selected because it 

will simulate the impact of the attached sunspace as a heat 

source for the building. The model was adjusted to reflect 

the materials actually installed and to optimize the design 

for the desired performance (interior temperature not below 

35 °F (1.7 °C)).

Iterative simulations were conducted to assess and optimize 

the effect of strategic design and materials applications on 

building energy performance. As a base case, the building 

was first simulated like a utility building without insulation 

5

Integrating Net-Zero Energy and High-Performance Green Building Technologies into Contemporary Housing in a Cold Climate

and minimal windows. Then insulation, south windows, 

and the sunspace were incrementally added to the model to 

parametrically assess and optimize building thermal performance.

Building parameters were adjusted as noted below for these 

various simulation schemes:

1. Base case building without insulation in the walls, roof, 

or foundation; omit south windows (at party wall to sunspace); omit sunspace (at party wall to sunspace modeled 

as exterior wall).

Figure 3. Carriage House cross section showing integration of structural components, solar energy (passive-thermal and active-electricity), and water storage. 

Figure 4. Interior view of the small-diameter log (SDL) structure, glulams, and tongue-and-groove decking.
solar production. The use of the thermal energy from the 

BioMax® for residential heating was not included in the Research Demonstration House but may be added as a retrofit.

Unlike fossil fuels, biomass fuels like wood pellets are 

largely carbon neutral, as they do not add CO2 to the 

atmosphere. This is because the same amount of CO2

released during the burning process is stored in the 

pellet’s source plant material while growing. The energy used to produce and transport wood pellets must 

be considered in their carbon footprint. The electrical power used to make pellets requires about 10% 

of the electricity produced by a given quantity of pellets. Were the electricity produced by the BioMax® 

(Community Power Corporation, Littleton, CO) used 

to charge batteries in an electrically powered vehicle, 

the transportation would be removed from the fossil 

fuel equation. Hauling wood chips 50 miles from forest to manufacturing site costs approximately $10 per 

ton for fuel and driver. If the costs for transporting 

pellets (higher density equals less expense per ton) to 

the BioMax® were on par with hauling chips from the 

forest, it would require another 10%. If the harvesting 

equipment and other energy users were all electric, it 

could be said that if 10 tons of pellets were produced 

it would require 2–3 tons of that material’s energy to 

make it honestly (not including producing the vehicle, 

equipment, or paving roads) carbon neutral. The electricity produced is net and not attributed to specific 

power producers.

Table 1 shows that the estimated average annual electric 

use for an energy-efficient home in Madison is 8,764 kWh. 

Together, these renewable energy systems (photovoltaic and 

BioMax®) can produce all of the electricity required including air conditioning on a net annual basis (PV ~4,500 kWh, 

BioMax® plus ~4,500 kWh at 50% of rated capacity) for a 

typical energy-efficient residence. Ongoing evaluation on 

the performance of the PV and BioMax® will be compared 

with the Research Demonstration House’s annual electrical 

energy use.

6

General Technical Report FPL–GTR–193

2. Building without insulation in the walls, roof or foundation; include south windows; omit sunspace.

3. Building without insulation in the walls, roof, or foundation; include sunspace.

4. Base building as-built with insulation; omit south windows and sunspace.

5. As-built with insulation and sunspace.

Table 3 delineates the insulation values of wall systems and 

materials used for the simulation schemes. Clear glazing is 

used on the south elevation and low-E glazing elsewhere. 

Heat pump heating was modeled in the simulation and no 

cooling was required. When modeling the sunspace, direct 

gain through the south windows of the sunspace party wall 

is not included (See Figs. 1 and 3.).

Installing 32 square feet of clear-glass south-facing windows 

produces a 7.5% improvement in building performance. 

Converting the windows to an attached sunspace with 

163 square feet of glazing and a temperature-operated 

fan to heat the building in scheme C produces a 10.9% 

(1,247 kBtus) improvement over the base case. Scheme D 

models the building with the insulation added as installed 

and at 61.3% (6,160 kBtus) creates the greatest jump in 

building energy performance. However adding the sunspace 

and insulating the building creates a synergistic improvement of 80.5% (9,231 kBtus) over the base case building, 

which is greater than the additive improvements would indicate. Figures 5 and 6 show the progressive improvement in 

building performance for simulation schemes A through E. 

The Carriage House was constructed per scheme E. A small 

electric heater is present to prevent freezing in an emergency.

Renewable Energy Systems

Two renewable energy systems are being employed and 

evaluated. One is a 3.7-kW roof integrated photovoltaic 

array mounted on the south-facing roof and is shown in 

Figure 1. Power is conditioned with a 4,000-W inverter. 

The electricity will be metered back into the local utility 

grid, taking advantage of a photovoltaic installation incentive program. The annual estimated energy production is 

~4,500 kWh. The photovoltaic system was sized to power 

most of the plug loads of a typical residence.

The second renewable energy system, housed in the west 

bay of the Carriage House, is a carbon neutral, wood-pellet 

gasification–electrical generation system (Walt 2004). The 

BioMax® is a 5-kW household scale system that uses wood 

pellets from wood waste to produce electricity (up to 

30 kW per day) and thermal energy in the form of heat that 

can be used for hot water or space heating. The manufacturer’s claim of up to 30 kW per day has not been verifiable 

in field evaluations. Systems evaluation and testing is ongoing. The electricity produced by the BioMax® complements 

the photovoltaic systems when electric use is more than 

Table 3—Insulation values for five energy 

performance modeling scenarios 

Insulation (U) values 

Scenario Wall Roof 

Foundation

[F2]

Clear 

window

Low-E

window

A 0.2669 0.2483 0.73 – 0.37 

B 0.2669 0.2483 0.73 0.49 0.37 

C 0.2669 0.2483 0.73 0.49 0.37 

D 0.0431 0.0432 0.70 0.49 0.37 

E 0.0431 0.0432 0.70 0.49 0.37 
7

Integrating Net-Zero Energy and High-Performance Green Building Technologies into Contemporary Housing in a Cold Climate

An analysis of the BioMax®’s potential to offset the winter heating demand indicates that the waste heat (thermal 

energy) generated by the BioMax® when it is producing 

electricity at half its rated capacity (15 kW per day) is equal 

to the one-half of a mid-winter day’s heating requirements 

for a typical energy-efficient home (~200,000 btu/day) when 

the outside temperature is 10–15 °F (–12°– –9 °C). At 50% 

heat recovery efficiency, the BioMax® would provide about 

a quarter of the peak winter day heating requirement for an 

average energy-efficient residence. In the summer, this thermal energy can supply all of the hot water needs, and since 

the BioMax® would be typically located in an outbuilding, the excess heat would dissipate via natural ventilation 

through building vents or open windows. Figure 7 shows the 

systems and equipment locations.

Rainwater Harvesting and Management

Rainwater harvesting is used to offset municipal water 

supply demand. The rainwater harvesting, management, 

filtration, and disinfection systems incorporated into the 

Research Demonstration House and Carriage House are 

designed to provide a secure and reliable water supply for 

all typical household water needs. Most of the water can be 

supplied by the harvesting system.

Both the literature and vernacular examples have validated 

the efficacy for using rainwater for all typical household 

uses. In cold climates like Madison, Wisconsin, irrigation 

needs are limited; therefore, harvested rainwater can be 

managed for potable and non-potable uses. Non-potable 

uses include washing clothes, flushing toilets (Fewkes 

1999), and bathing. Potable uses of rainwater have been 

shown to be viable with disinfection and quality monitoring.

Any comprehensive rainwater harvesting and management 

program must consider the climate, physical and site constraints, and technical considerations including water quality 

and local regulations in addition to cost. All will have an 

effect on system design.

The duration of storage in a cistern coupled with first-flush 

systems, which divert the first few gallons of catchment 

runoff, have been shown to produce water with quality measures that meet or exceed municipal drinking water standards. However, disinfection technologies are recommended 

for potable use of this water. Disinfection methods include 

thermal (Birch and Thomas 1998), chemical (chlorination), 

ultraviolet treatment (Abbaszadegan and others 1997), or a 

combination of these.

Figure 5. Carriage House monthly heating demand for the 

energy simulation scenarios.

Figure 6. Total annual heating use from the energy simulation scenarios.

Figure 7. Carriage House floor plan showing location and 

relationship of systems.
8

General Technical Report FPL–GTR–193

The water harvesting systems in this project demonstrate 

state-of-the-art technologies for using rainwater to offset 

municipal water demand and potentially provide all household water needs in emergency situations, providing a level 

of water security. Average total household use (family of 3) 

in Madison is 192 gallons (0.73 m3) per day (Madison Water 

Utility 2001). On an annual basis, this is 70,080 gallons. The 

rainfall harvest potential for this project’s 3,200 ft2 (297 m3) 

house is approximately 61,835 gallons (234 m3) annually, 

given Madison’s 31-in. (0.79-m) average annual rainfall. 

Average rainfall was calculated from Madison, Wisconsin, 

1960–1995 rainfall data (NCDC 2010). Thus, effective management of rainwater harvest could supply over 75% of the 

water demand for a family of three in Madison (Fig. 8).

Because of rainfall variability, volume, and the cost for constructing storage, the Carriage House cistern was size optimized via an input–output model that considers rainfall frequency and volume from the rooftop collection area with the 

water use rate for a typical Madison residence. When rainfall is in excess of use rate and storage capacity, it overflows 

into a subsurface drain field south of the Carriage House.

The rainwater management systems in this residential demonstration project are designed to address potable and nonpotable uses separately.

Non-Potable System

Since toilets and clothes washing comprise about half of the 

average daily use (Table 2), the non-potable rainwater system can reduce water use significantly depending on rainfall 

frequency and duration and the size of the associated storage 

compared to demand. This system (Fig. 9) was designed 

and configured to be compact for installation inside the 

Research Demonstration House. The close proximity to the 

laundry area and bathroom facilitated connection to these 

non-potable uses. It includes a 300-gallon tank that stores 

rainwater from a portion of the adjacent roof. The tank is fitted with an overflow for excess rainfall. The control system 

includes a demand-activated pump and relayed valve connection to the municipal supply with appropriate back-flow 

prevention. A low water level sensor in the tank connects to 

the control relays. When rainwater in the tank falls below 

the sensor level, the control system closes the tank output 

valve and opens the valve from the municipal supply. This 

system is designed to be used in areas where rainfall frequency does not provide a reliable supply. Maintenance and 

management of this system is limited to seasonal cleaning of 

the tanks and testing of the back flow preventer that isolates 

rainwater from the municipal system.

Filtration/Disinfection System

This rainwater collection system was specifically designed 

to determine the efficacy of producing high-quality water 

via a point-of-use (POU) water treatment device. It is comprised of six components, collection, detritus removal, transport, storage (see sidebar on rainwater quality), filtration/

disinfection and operable connection to the household supply. Rainfall is collected from the roof into gutters and gravity fed to downspouts. The downspouts are fitted with leaf 

diverters and equipped with first-flush devices to remove 

particulates as described in the sidebar on first-flush devices. 

Figure 8. Chart of rainwater harvest potential by number 

of persons in household showing the percent of harvested rainwater that would be available as the number 

of persons in the household increases. The Madison 

average indoor use rate is gallons per day at 68.7, with 

3,200 ft2 catchment.

Figure 9. Non-potable rainwater storage and management systems for flushing toilets and washing 

clothes.
9

Integrating Net-Zero Energy and High-Performance Green Building Technologies into Contemporary Housing in a Cold Climate

Overflow from the first-flush devices is piped (underground) 

to the cistern. The main cistern (2,500 gallons, 9.5 cubic 

meters) is located under the east bay of the Carriage House 

(Fig. 7). Rainwater is pumped from the cistern through a filtration/disinfection apparatus. Figure 10 is a diagram of the 

filtration/disinfection systems and Figure 11 illustrates the 

actual system with interpretive materials. The filtered and 

disinfected water is routed back to the Research Demonstration House and connected into the municipal water supply 

line with appropriate valving and back flow prevention so 

that either municipal water or filtered/disinfected rainwater 

is supplied for the household uses. Rainwater in excess of 

the cistern storage capacity overflows to a subsurface leach 

field south of the Carriage House. 

Potable Water 

The point-of-use filtration/disinfection system was assembled from off the shelf filtration and UV disinfection 

units as shown in Figures 10 and 11. The components of 

the system included a typical pressure pump/tank system, 

a 20-μm spun polypropylene progressive-density cartridge 

filter, a 20-in., 5-μm spun polypropylene progressive-density 

cartridge filter, an activated carbon impregnated paper cartridge filter, and a high-capacity ultraviolet sterilizer. The 

UV module is equipped with a 22-W UV lamp. These components are mounted on a board as part of an interpretive 

display (Fig. 11). This system was assembled and filtration/

disinfection performance was evaluated at the University of 

Arizona’s National Science Foundation Water Quality Center (Jordan and others 2008). The filtration and disinfection 

performance evaluation compared heterotrophic plate count 

(HPC), turbidity, pH, total organic carbon (TOC), and total 

dissolved solids (TDS) measurement taken from the following water types: first flush, stored cistern water, and water 

passed through point-of-use filtration and UV disinfection 

units separately (Fig. 12). 

Point-of-use water treatment systems similar to the one developed for this project have been demonstrated (Adams and 

others 1987; Wolf 1990; Pozos and others 2004; Jordan and 

others 2008) to be an effective and practical option for purifying water against known bacterial, viral, and protozoan 

pathogens. Linden and others showed effective inactivation 

of protozoan cysts when treating a variety of water sources 

with a low UV dose similar to that imparted by our UV disinfection unit (Linden and others 2001).

Perhaps the issue of most concern for potable use of harvested rainwater is maintenance and monitoring of the filtration/disinfection unit. It is not uncommon to see heterotrophic regrowth in these point-of-use devices (Adams and 

others 1987; Morin and others 1996). We plan to alleviate the 

regrowth of heterotrophic bacteria by constantly bleeding a 

portion of the filtered water back into the cistern to prevent 

filter fouling. The other option we will use as necessary is to 

disinfect the unit with monochloramine.

Rainwater Quality

Research has shown that the quality of roof-harvested 

rainwater depends on many factors. Water quality in 

rainwater management systems starts at the rainwater 

catchment surface and continues to the storage tank 

and on to the filtration/disinfection unit.

The roof surface material is very important. Reflective roof coatings should have a potable use rating 

(NSF International 2007). NSF International (www.

nsf.org/) has developed a protocol that tests materials used in rainwater catchment systems. Testing 

involves exposing catchment system products (i.e., 

roofing materials, coatings, paints, liners, and gutters) to extensive accelerated outdoor weathering. 

Products meeting the requirements of this protocol 

are deemed not to impart contaminants to test waters at levels greater than those specified in the U.S. 

EPA’s Drinking Water Regulations and Health Advisories (EPA 2006). Rainwater harvested from newly 

roofed buildings should be tested periodically before 

processing for potable use. Asphalt shingles and zincplated roofing systems, for example, produce undesirable residuals for some time after installation. Lead 

flashing should be avoided. Care should also be taken 

to clear the catchment surface of any debris, including litter from overhanging plantings and biological 

waste from birds as they are the primary depositors of 

pollutants in roof rainwater harvesting systems. Also, 

the catchment surface should be cleansed from time 

to time to prevent build up of particulate debris from 

local air pollution, including dust and residuals from 

automobiles and industry. Leaf litter can be managed 

with plant maintenance, whereas dust, air pollutants, 

and animal waste should be addressed by means of a 

first-flush system. Many devices have been developed 

for achieving first flush; most are viable but all require 

continued monitoring and maintenance. Also, the intake from the cistern to the filtration system should be 

six inches or more from the bottom to prevent intake 

of sediment. Regular tank cleansing and maintenance 

is also recommended.

First-Flush Devices

A number of first-flush devices were evaluated for 

their performance and seasonal use. In general, all of 

the first-flush devices tested collect a measured volume of initial roof drainage to prevent dust and debris from roof and gutters from entering the cistern. 

When the determined flush volume is reached, the 

rainwater is passively diverted to the cistern and the 

initial (dirty) water drains from the device’s storage 

container.
10

General Technical Report FPL–GTR–193

The devices evaluated range from simple configurations of off-the-shelf PVC pipe and fittings to marketed products that are adaptations of the basic PVC pipe 

configurations that add plastic balls to seal the route to 

drain, diverting the clean water to storage.

In one product, the ball closes rainwater flow to flush 

storage tanks and includes fittings to allow slow drainage of initial (dirty) rainwater from the tank. The volume of first flush for this system is determined by 

the size of the tank. This first-flush device is from an 

Australian company (Rain Harvesting Pty, Ltd., Archerfield, Australia) and comes in a number of configurations for application flexibility. One problem we 

noted was with dimensional differences between PVC 

sizing in the United States and Australia causing problems with fitting connections.

The other product is a ball modified to take fill with 

water when the rain begins. The ball modifications include an adjustable, screened intake, and a drip hole 

for drainage. It also has an attachment loop on top and 

includes a spring, suspension bar, and gasket ring. It 

is installed into a 4-in. polyvinyl chloride pipe fitting 

(PVC-T) below the diversion to the rainwater storage. 

Its operation uses the initial roof drainage to fill the 

spring-suspended ball with water. As the weight of the 

ball increases, it drops into the gasket closing the path 

of water to the drain. Additional clean rainwater backs 

up and is diverted to the rainwater storage tank. At 

the end of the rainfall, the ball drains completely via a 

drip hole allowing the spring to raise the ball, readying 

the diverter for the next rain. The first-flush amount is 

adjusted by changing the opening to the intake screen. 

A problem noted with this product is that the dust/silt 

in the initial roof runoff causes clogging leading to 

device malfunction.

Other devices are available that allow detritus to pass 

through. They depend on surface tension to move rainwater traveling down a pipe through a fine screen to be 

diverted to storage. However, the cost of these devices 

made them unpractical for residential application.

In a cold climate like the project site, ice build-up can 

lead to downspout failure. Initial research indicated 

that such failures would be magnified in first-flush 

devices that were installed outdoors. To evaluate the 

extent and impact of such failures, two outdoor firstflush devices were installed in fall 2008. In addition, 

one was installed indoors. The two outdoor installations failed because of ice build-up from diurnal thaw/

freeze cycles. After confirming the failure, we recommended decommissioning the rooftop rainwater harvesting systems unless the first-flush device could be 

located indoors. However, even the indoor application 

has the potential for freeze/thaw ice build-up failures 

in the external plumbing, either in the leaf catcher or 

in the pipe that carries the water to the interior.

Discussion

Residential photovoltaic systems are becoming more affordable through incentives, improved technology, and 

acceptance. Energy efficiency in building envelope design 

is recognized as an essential part of the sustainable energy 

equation. Together they provide the opportunity for moving 

closer to net-zero energy at the residential scale. Advances 

in building energy modeling and cost reductions in photovoltaics are helping to move these technologies into the 

mainstream. Yet, many remain skeptical or do not understand how these work together. This project is accessible to 

the public and is designed to help bridge the gap between 

research and application.

Rainwater harvesting and use has even older roots in the 

traditions of the region. But its acceptance as a viable water 

resource is diminished by the availability of water from municipal utilities. This project is designed to showcase how 

technology can bridge the gap between the traditional use of 

rainwater and a contemporary source for residential water 

needs whether for irrigation, non-potable household uses, 

and even potable use through careful development and management of the filtration/disinfection system.

Finally, climate change and unforeseen consequences in 

early fire management policies has placed challenges to our 

perception of how we manage forest resources. A shift in 

forest management strategy has created a new resource in 

woody biomass from the slash and small-diameter logs that 

Figure 10. A schematic depicting the basic components 

making up the point-of-use water filtration and UV disinfection unit.

1 Water from cistern

2 Bleed line to cistern

3 Filtered water to house

4 Pressure tank

5 Pump

6 Sample port

7 Pressure gauge

8 System drain

9 Bleed line control valve

A 20-Micron filter

B 5-Micron filter

C Charcoal filter

D UV Disinfection
11

Integrating Net-Zero Energy and High-Performance Green Building Technologies into Contemporary Housing in a Cold Climate Figure 11. Graphic illustration of the rainwater filtration/ disinfection systems with interpretive materials and illustrations.
12

General Technical Report FPL–GTR–193

may be processed into useful forest products. The slash can 

be used in new technology like the BioMax® for heat and 

energy production, and the products from small-diameter 

logs should be developed and integrated into the building 

industry instead of being land filled.

Showing how these systems work and can be effectively 

integrated through collaborative design, engineering, and 

technology development is an essential part of this effort. 

The Research Demonstration House at FPL will help interpret this idea.

Conclusion

This project has shown that the integration of building 

systems with renewable energy and rainwater harvesting 

systems can achieve net-zero energy on an annual basis 

for electric requirements including air conditioning. The 

total energy requirement including heating may be further 

reduced through the incorporation of waste heat recovery 

from the BioMax® system. The national goal of 50% reduction in municipal water use can be met by conservation and 

through the use of rainwater for non-potable demands for an 

average family of three. This research has shown that with 

adequate collection area, storage, and filtration/disinfection 

to potable standards, the water needs for an average family 

in cold climates can be met through the use of rainwater. 

However, current water infrastructure safety requirements 

do not allow other water sources to be connected to the municipal systems because of concerns for the maintenance of 

water quality. Rainwater harvesting systems developed for 

potable use must be continually monitored to assure water 

quality and safety.

This project validates that (1) the grid-interconnected combination of the BioMax® wood-pellet energy system (5-kW 

generator with battery storage and inverter capable of 

10 kW with solar energy via photovoltaics (3.7 kW) can 

provide all of the power needs for a residential unit in a cold 

climate; (2) rainwater can be stored (2,500-gallon cistern) 

and reliably filtered and disinfected for potable use; (3) systems for renewable energy and water are safe, reliable, and 

provide water security that is not dependent on community 

infrastructure; and (4) these technologies are available and 

work well in cold climates like Wisconsin.

As the interest in sustainability increases and technologies 

such as those shown and evaluated in the project become 

more available, affordable, and acceptable, the payback 

periods for such fully integrated sustainable systems will 

become shorter. More importantly, the impact of this project 

is expected to be in demonstrating the possibilities and potentials for the development of sustainable energy and water 

in a residence in the cold winter conditions of the upper 

Midwest.

Acknowledgments

This research and demonstration project was made possible 

through a cooperative agreement between the University of 

Arizona (UA) and the U.S. Forest Service, Forest Products 

Laboratory (FPL), Advanced Housing Research Center. 

Technical support was provided by the UA National Science Foundation Water Quality Center at the University of 

Arizona’s Environmental Research Laboratory. Architectural design assistance was provided by Stephanie Gerstle, 

American Institute of Architects, Tucson, Arizona. Beaudette Consulting Engineering (Missoula, MT) performed the 

structural analysis for the small-diameter timber framing. 

The grid interconnected photovoltaic power system was provided by Wisconsin Power Control (Madison, WI). Product 

suppliers who provided discounts included Andersen Windows (Andersen Corporation, Bayport, MN), McElroy Metal Service Center (Madison, WI), and Rain Harvesting (Aurora, IL). The small-diameter logs for trusses and columns 

and laminated tongue and groove decking of ponderosa pine 

from fire wise forest thinning were provided by Steve and 

Randy Nicoll of ASL Beam and Cheyenne Log Homes of 

Eager, Arizona. Special thanks to Doug and Bart of Richter 

Construction, Arena, Wisconsin, the project contractor, for 

their flexibility and creativity. Finally, we acknowledge the 

critical technical advice, expertise, and support provided by 

FPL facilities engineering and staff.

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13

Integrating Net-Zero Energy and High-Performance Green Building Technologies into Contemporary Housing in a Cold Climate

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