Duplex

The 7th street Duplex in Missoula, MT was an infill project built in 2008 with some very specific goals in mind. The site was relatively small at 4800 ft in central Missoula in a well established neighborhood. The infill lot has houses on either side of it that are single story older homes, so one of the goals was to try and impact the existing neighborhood as little as possible, while still striving to create a long-term investment property. Through designing a single story prairie style home with low pitched roof and strong horizontal lines, we felt that this would provide for the least visual impact as possible. Other goals of the project are as follows:

GOALS:

• Superinsulation/Low Energy Usage
• Optimal Indoor Air Quality.
• Use of Durable products that require little maintenance.
• Use of non toxic materials whenever possible.
• Wise water management in the building and through native landscape design and implementation.
• Use of local materials and vendors to support Missoula’s economy.
• Construct it for a cost of less than $100/ ft
• Use as an educational tool for future projects.

BUILDING DETAILS TO ACHIEVE GOALS:

• Building Envelope:  Autocad Detail

• Mechanical Systems:
  • Venmar HE 1.3 High Efficiency HRV for each unit. Stale air exhausted from each bathroom, kitchen and laundry. Fresh air delivered to each bedroom, living and dining room. Filter can installed on fresh air intake to eliminate any pollutants at exterior of building.
  • Fujitsu Ductless minisplit system designed to satisfy heat load down to 5 degrees Fahrenheit.  Free standing gas fireplaces installed to provide heat when minisplit systems shut down. Peak heat load = 7000 btuh at -9 F design temp.
  • Tankless gas water heaters for domestic hot water. All hot water fixtures within 25 ft of hot water heater.
• Durability management:
  • overhangs on roof system to protect building from moisture
  • Vented cladding assembly with air space behind siding.
  • Fibercement siding and exterior trim. All end cuts pre-primed prior to installation.
  • Sealed vapor barrier under basement slab to protect building from moisture and radon gasses
  • Sealed foundation membrane to protect exterior foam from damage and moisture
  • Stairway to downstairs unit = concrete + powder coated handrails for low maintenance
  • Metal clad wood windows with triple glazing= low maintenance exterior and low potential for condensation on interior
  • Sealed stained finished concrete floors and counter tops
  • All plywood box cabinets
  • Galvanized metal from bottom of cladding to grade to protect foam
  • Proper drainage away from building
• Non Toxic Materials
  • Fly ash concrete for foundation and flatwork
  • Non toxic finishes for paint and sealed concrete
  • No formaldehyde products (All plywood boxes for cabinets, Concrete counters, wire shelving, formaldehyde free trim)

• Indoor Air Quality
  • Continuous supply of fresh air through Heat Recovery Ventilation system. Exhaust air pulled out of bathrooms and kitchen. Fresh air delivered to each bedroom and living areas.
  • High speed override switches for spot ventilation in bathrooms and kitchen.
  • Range exhaust ducted to outdoors.
  • Sealed combustion on demand water heater.
  • Direct vent free standing fireplace.
  • Non toxic materials used
  • No carpet to collect dust and other contaminants.
• Water Efficiency
  • Lo flow fixtures used throughout
  • Native landscaping design uses very little irrigation.
  • All irrigated plants are on drip system for efficient use of water.

Results and Lessons Learned:

• Construction cost came in at right around $95/ft2
• Occupants are extremely satisfied with overall comfort and indoor air quality.
• Utility usage for heating is very low for the building. Cost around $30/month for space conditioning.
• Occupant behavior dramatically affects overall utility consumption. One tenant is mindful of energy usage and consumption is generally 30% less than other tenant.
• Building Envelope Lessons:

• • It would have been easy to add more insulation under the slab in the basement.
  • The embodied energy and ozone depletion potential of the spray foam is hard to justify. With a qualified construction team, use of dense cellulose in the wall cavity is a much greener material. On future projects I will recommend the use of as little spray foam as possible.
  • The front porch dramatically reduces the passive solar gain possibility on the south side
  • The windows on the front should have been tuned to allow more solar heat gain.
  • The controls of the ductless minisplit changeover to fireplace during temperatures below 5 is difficult to manage. The use of a hydronic or electric coil in the HRV duct system would have been a simple inexpensive and efficient way to heat the building.

CONTACT US – Energetechs, Inc., – ph.