Victorian net zero renovation

Project Subtitle: 

Net Zero Victorian

Project Description: 

Two retired professors, Linda and Stewart Herman, wanted to show that a standard city house on a standard city lot in chilly Minneapolis could be renovated to net zero in energy with no sacrifice in attractiveness, space or comfort.  These goals were achieved with the 2015-2016 renovation of a 1907 balloon-frame house on a 40x130-foot lot in the Whittier neighborhood.  Design was by SALA Architects of Minneapolis, MN; engineering by Align Structural of Minneapolis, and construction by Morrissey Builders of St. Paul, MN. 

The four 'legs' of our net-positive house:

a. 54 solar collectors (42 on house, 12 on garage) for a 17kW capacity;

b. 4 250' deep geothermal wells in a 30 x 40 foot backyard;

c.  Insulation: PERSIST exterior insulation system (R-40 in the walls, R-80 in the roof) and the Cocoon system for insulating the basement from exterior (R-30), and triple-glazed windows throughout.

d. Tight envelope: 3M ice-and-water plus extensive sealing around all openings keeps the infiltration rate to 350 at CFM50, or .05 CFM per square foot of building area shell surface.  It exceeds code for tightness by five times.

To save energy, the house uses a geothermal heat pump, a heat-pump driven water heater, and a ventless heat-pump driven dryer.  It is ventilated by an ERV (drawing exhaust air from kitchen and bathrooms).  When the range hood operates, cooler makeup air is drawn past the refridgerator coils for more efficient cooling.  The wallboard is of a new type (Certainteed 'Air-Renew') that absorbs formaldehyde for a promised ten years. All lighting is LED, whether in traditional fixtures, cans or other locations. 


The interior of the total gut rehab involved a) retaining the original birch flooring (first floor) and installing recycled maple flooring harvested from three Twin Cities houses being demolished (2nd floor).  The original yellow-birch millwork (window, door casings and baseboard) was refinished and reinstalled. Supplementary millwork is also regionally sourced yellow birch, milled in the same design as the original.  For the comfort of the retired couple that lives there, the stairwell was widened to 4 feet and key doorways to 3 feet for wheelchair access.  The bathrooms have rails, the cabinets have pull-outs, the drawers are soft-close. 

'Aging in place':  Since the owners are already in their later 60s, and hope to live in the house for as long as they are able, the house incorporates many design features from the National Association of Homebuilders to enable occupants to live in a house well into their old age: an easily rampable rear entry, on one level; 36" wide doorways to accommodate wheel chairs; wide turning places; a 4-foot wide stairway between floors; soft close cabinets in kitchen, base cabinets with pullout shelving; easily manipulable faucets; wall-mounted toilets (for easy cleaning); bright LED lighting throughout; sensor lighting on exterior; lever door handles on exterior doors; low-maintenance exteriors including porch decking; washing and drying machines raised 12" above floor; side-by-side refridgerator; laundry chute; grab bars in bathrooms including shower and tub; brightly-lit closets; etc.


The yard is bordered by hardscape--Versalok blocks capped with NY Bluestone (also used for the front walk and terracing).  2500 square feet of the yard is planted in a variety of Minnesota perennials, mostly drought tolerant.  A three-zone drip irrigation system is installed to carry these plantings through a dry summer.  A much smaller slice of the yard is planted in Kentucky bluegrass, with no installed irrigation.


Building Type Summary: 

single-family residence

Other Awards: 

10th Annual Green Home of the Year Award - Green Builder


2021 Harriet Avenue
Minneapolis, MN 55405
United States



Lat. / Long.: 

POINT (-93.2851629 44.9619735)

Location Type: 


Climate Region: 

Zone 6

Occupancy Type and Details: 

home for retired couple. Live here all year around; not snowbirds.

Number of stories: 


Conditioned Floor Area: 

3 640

Conditioned Building Volume: 

32 544

Unconditioned Floor Area: 


Multiple buildings?: 

Total number of units in project (all buildings): 


Total floor area of project (all buildings): 

3 640


Completion date: 

Thursday, December 1, 2016

Site description: 

Typical tired old urban house on typical urban plot (40x 120)


Flooring and millwork were regionally sourced (Wisconsin)
low-VOC paints
wallboarding that absorbs formaldehyde

HERS Index: 


Annual renewable energy generated: 

17 000

Power Rating: 

17 000Watts

Electric Utility Company: 

Xcel Energy

Gas Utility Company: 


Datasets and Utility Bills sources and reliability: 

utility bills, presumed reliable

Electricity amount (imported from grid): 

8 062

Electricity amount (credited or exported to grid): 

14 378

Net electricity usage (purchased electricity): 

8 062

Energy Storage Capacity: 


Energy Storage type: 


Subslab assembly: 

Basement floor removed; new slab poured on top of 2" foam.

Slab edge assembly: 

"Cocoon" system: pressure jet and vacuum used to excavate 4" around foundation, down to footing. Then 1" EPS foam inserted, and the gap between foundation wall and foam sheet was filled with more foam squirted in.

Foundation wall assembly: 

Existing foundation variously reinforced concrete or stone. Little R value.
"Cocoon" system: pressure jet and vacuum used to excavate 4" around foundation, down to footing. Then 1" EPS foam inserted, and the gap between foundation wall and foam sheet was filled with more foam squirted in.

Above grade wall assembly: 

joists extended to provide support for new exterior wall. See PERSIST description above

Cathedral ceiling assembly: 

Attic space has no insulation in floor. All insulation above inner (old) roof.

Door Area: 


Space heating - Manufacturer & Model: 

Enertech Geocomfort GYT036A11MT1CSS heat pump

Space cooling - Manufacturer & Model: 


Domestic hot water - Manufacturer & Model: 

AO Smith HPTU 50 N 120

Domestic hot water - capacity: 


Ventilation - Manufacturer & Model: 

Broan ERV250 ECM


mid-2014 competitive selection of architect
late 2014-mid 2015 - from conceptual to construction drawings

Design for Adaptability: 

blueprints retained but idiosyncratic to this particular house renovation

Gross Cost of Renewable Energy System: 

120 000

Value of Tax Credits for renewable energy systems: 

40 000

Net Cost of renewable energy systems: 

80 000

Federal incentives: 

1/3 for solar and geothermal systems

Utility incentives: 

surplus solar power purchased by utility for ~10 cents per kWhr
Solar Rewards (Renewable Energy Certificates) purchased for 8 cents / kWhr

Annual Electric Savings: 

1 500

Annual Revenue from SRECs or other renewable energy credits: 

1 400


Go for federal incentives and utility incentives!


ILFI net zero (December 2017)
Green Home 'zero hero'
LEED Platinum (May 2018)

NESEA Awards: 


Published References: 

Special architectural measures: 

modest passive solar--extended eaves
solar heat gain/loss film on windows optimized for window location

Energy Use and Production Documentation: 

Subslab R-value: 


Slab edge R-value: 


Foundation wall R-value: 


Above grade wall R-value: 


Average window U-factor: 


Solar Heat Gain Coefficient: 


Air Changes per hour, ACH50: 


Number of Bathrooms: 


Scope Description: 

Total gut rehab, affecting 99% of structure

Site conditions: 

preexisting structure(s)

Renewable Energy Sources: 

Renewable energy is generated within the building footprint (e.g. solar PV on the roof)

Summary of enclosure strategy/description: 

PERSIST concept (Canadian): insulate exterior of house. Strip down to sheathing; apply ice and water, then 7.25" EPS foam in 4x8' blocks. Then apply 5/8" plywood for strength. Then Tyvek. Then furring strips. Then lap siding. See pictures

Roof Assembly: 

Old roof retained; new roof built over. Ridge beam (18" x 6") inserted under peak, supported by steel posts running down interior of interior walls to reinforced concrete pads in basement. New roof consists of 14" high OSB I-beams, 21" on center, gaps filled with about 10" of squirted foam (LaPolla). Then 2x6"s laid vertically crosswise, and plywood attached to them. Large air space kept, vented at eaves. Roofing is 30-year shingles. Total R-value is 80, including batt insulation tucked into 2x6"s under old roof.

Roof R-value: 


Window Description: 

Anderson Windows& Doors. A- series, all triple-glazed.

Door Description: 

Andersen Windows & Doors.

Mechanical Equipment Installation Details and Comments: 

heat pump for HVAC - COP 5
350 CFM50 (heating and cooling) as measured by blower door test

Number of Bedrooms: 


Team Members: 

Marc Sloot, SALA Architects, Minneapolis.
Katie Leaf, SALA
Sean Morrissey, builder



Basis of Performance Claim: 

Zero Energy Program

Type of Construction: 


Renewable Energy System Type(s): 


Renewable Energy System Description & Details: 

54 LG 315 watt panels, 42 on house, 12 on garage SolarEdge inverters and DC optimizers

Annual Renewable Energy Generated Data Type: 


Source of Annual Production Data: 

metered by Xcel (utility)

Space Heating - Efficiency (e.g., 92 AFUE): 


Space Cooling - Efficiency (e.g., 16 SEER): 

29.1 EER

Air Changes per hour, CFM50: 


Days per year Building is fully occupied: 


Submitter Contact Email: 

Submitter Contact Phone Number: 

(701) 541-9172

Project Type: 

Net Exporter

Lighting Manufacturer and Model: 

all LED

Indoor Environment Description: 

no added urea to kitchen cabinetry wallboarding designed to absorb formaldehyde active radon venting --collected in sump, vented through roof continuous airflow into house via ERV, with heat exchange.