Case Study

Cape Coral, florida

Builder Achieves HERS 15 on First High-Performance Home

Ravenwood Homes built its first high-performance home in southwestern Florida in 2011. A Building America design team consisting of Pacific Northwest National Laboratory, Wright Jenkins Home Plans, LLC, and Florida HERO assisted him in designing and building a home that ultimately achieved a HERS of 15. Not counting the nearly 6 kW solar Photovoltaic system, the home would achieve a rating of 65.

This builder’s experience demonstrates how important installation details are in avoiding thermal bypasses and maintaining a fully aligned air barrier and thermal barrier. For example, the builder initially used inset stapling to secure kraft-faced insulation in the walls, which creates creases in the face of the insulation that serve as potential pathways for air movement. This problem had to be corrected before drywall was installed. In addition, the builder installed 72 recessed can lights in the home rather than the 12 specified in the design. Although the can lights were sealed to the drywall, this change pushed the originally anticipated building infiltration rate of 2.0 ACH50 (air changes per hour at 50 pascals of pressure) to 4.39 ACH50, or more than twice what had been expected.

This home, as Ravenwood’s first, was more expensive than it needed to be and did not have a positive cash flow, despite the good energy performance. As the builder becomes more familiar with high-performance building practices and develops relationships with equipment suppliers, costs should come down and result in significant cost and energy savings in future high-performance Ravenwood homes.

Key Energy-Efficiency Measures:

HVAC:

• SEER 16 AC with strip heat (little heating load in south Florida)

• All ductwork in conditioned space.

• Positive pressure whole-house ventilation system (run-time only) all exhaust fans vented to outside.

Envelope:

• Concrete block with 1-in. rigid foam insulation applied to the interior of the block wall with furring strips and drywall on top for some exterior walls. 16-in. on-center wood frame with R-19 fiberglass batt insulation on remaining exterior walls

• Vented attic with R-38 fiberglass batt insulation on the attic floor and radiant barrier on the roof deck

• Low-E vinyl windows (U = 0.26–0.55, SHGC = 0.18–0.70) Moderately tight building envelope, ACH50 = 4.39

Lighting, Appliances, and Water Heating:

• 100% compact fluorescent lighting

• ENERGY STAR® appliances

• Solar thermal with 120 gal tank Open Loop Direct System (2) 4-ft x 8-ft panels

• 26-panel PV array, 5.98 kW
  

Lessons Learned

• Ducts in conditioned space and the ceiling air barrier were instrumental in achieving moderate air leakage rates and scoring well on the HERS Index, although additional can lights penetrated the ceiling in many locations.

• Training was important for the installer to achieve best practices. Involving the builder, designer, and building science consultant in the training of all onsite workers helped to meet efficiency goals.

• Design decisions made in the field can dramatically influence energy performance. In addition to the recessed can lights, changes for this house included the addition of a swimming pool pump, downgrading the AC system, and installing a smaller PV array.

Performance Data