The Davis House

Project Subtitle: 

Somerville, MA

Project Description: 

This renovation transformed this building from an energy guzzler to a resilient and healthy spacious 2-family, designed to use less energy than it produces. Careful planning resulted in high efficiency of the building envelop, of the heating, cooling and ventilation systems. The solar panels provide the energy needed to run this two family.

This is important because:

Existing structures, outnumbering new housing nearly 300-to-1

"The greenest building is the one that’s already built, in almost every case.”

There are 130million housing units that already exist. 80 % will still be here in 2050. This is where many of our efforts should be.

The goal was to reduce the energy use and increase the usability of the building within the same footprint by:

New envelop:     Roof R-60 to 62.5, Walls R-48, Bsmt-Walls R-23, Slab R-20 3 pane windows: (SW,
NW,NE) U 0.21, SHG 0.19, VLT 0.32
(SE) U 0.25, SHG 0.31, VLT 0.34
Retained 60% more solar gain on the SE for passive solar heat.

Windows added by 50% to South, removed by 50% to North

Provided solar shading ACH .85 to 1.2 @ 50P
Equipment:
A hybrid solar system with 56 Sunpower solar panels for PV combined with 12 Sundrum panels attached
under the PV panels provide power and hot water. The hot water is for
both domestic use and for the basement radiant slab.

3 minisplits per unit provide both heating and cooling.
Each unit has a HRV which provides preconditioned air to  all rooms and works with booster fans to
exhaust bath and kitchen air. The condensing washer-dryers don’t require an exhaust fan. With these
strategies we minimized the number of exterior envelop penetrations from the mechanical equipment
and provide for a much healthier indoor
environment with constant fresh air supply

Each unit has a HRV which provides preconditioned air to  all rooms and works with booster fans to exhaust bath and kitchen air. The condensing washer-dryers don’t require an exhaust fan. With these strategies we minimized the number of exterior envelop penetrations from the mechanical equipment and provide for a much healthier indoor environment with constant fresh air supply.

Layout:
Redesigned layout with combined rooms for spaciousness. Expand interior to exterior with decks and added windows. Expand living space to basement & in attic by lowering floors and adding daylight.

Minimize visual clutter, use transparent materials (see stairs).The sustainability of the design is enhanced by resource efficiency: many of the building materials used are reused or recycled, for example bathroom floor tiles are the former slate roof. The floors were reinstalled. Demolished chimney bricks were reused. One staircase was rebuilt, a stair and cabinet built with wood from a nearby demolition site, recycled ceramic tiles and recycled tire decking etc.

The healthy indoor environment is due to using no or low off-gazing building materials and a continuously operating ventilation fan supplied preheated out door air. The redesigned room layout assures the spacious feel for the interiors. Although the apartments are small, about 1360 SF, with a lot of daylight and transparent adjacencies between the non-private rooms, the space feels generous. New decks also expand the interior spaces to the exterior.

Recycled furniture in both apartments complete the sustainability of the project.

Building Type Summary: 

2-family residence

Address: 

13 Elmwood Street
Somerville, MA 01244
United States

Elevation: 

50

Lat. / Long.: 

POINT (-71.126418 42.4000709)

Location Type: 

Urban

Köppen Climate Type: 

Dfb

Climate Region: 

Zone 5

Solar Insolation: 

4.47 kWh/m2/day

Annual HDD : 

5754

Annual CDD: 

1016

HDD Base Temp: 

68

CDD Base Temp: 

75

Occupancy Type and Details: 

4 people occupy the building for 350 days/year

Conditioned Floor Area: 

3 130

Multiple buildings?: 

Historic?: 

HERS Index: 

-4

Annual renewable energy generated: 

8 586

Power Rating: 

7Watts

Electric Utility Company: 

NSTAR Electric

Electricity amount (imported from grid): 

47 702

Electricity amount (credited or exported to grid): 

46 652

Net electricity usage (purchased electricity): 

45 084

Space heating - Manufacturer & Model: 

mitsubishi

Space cooling - Manufacturer & Model: 

mitsubishi

Domestic hot water - Manufacturer & Model: 

Solar Thermal System, 120 gal solar tank with 4500w electric backup

Ventilation - Manufacturer & Model: 

Lifebreath

Total Cost of Project: 

761 064

Energy Use and Production Documentation: 

Foundation wall R-value: 

23.00

Above grade wall R-value: 

48.00

Average window U-factor: 

0.21

Solar Heat Gain Coefficient: 

0.19

Cost per square foot of Conditioned Space: 

167.00

Roof R-value: 

60.00

Project Team: 

Architect

Team Member: 

Franziska Amacher

Status: 

Live

Weight: 

0