Homes built prior to 1980 make up 80% of the housing stock in the United States, and are responsible for a majority of the residential energy use in the country. The Architecture 2030 goals call for a 50% reduction in home energy use by 2010. The objective of this project was to show that a 50% reduction in home energy use could be met today in existing housing. All systems were in new of updating, including plumbing, electrical and heating. Using systems engineering techniques, the enclosure and mechanical systems were analyzed to determine the most cost effective ways to meet this goal. Care was taken to provide proper water management details as the additional insulation was added.
Project Team: Building Science Corporation
Address: West Concord, Massachusetts
Description: 3,600 ft2 two-story, 4 bedrooms, 31/2 bath single family home
Completion Date: October 2008
Annual Utility Costs:
Gas before retrofit: $2,400/year
Gas after retrofit: $858/year
Electric before retrofit: $960/year
Electric after retrofit: $471/year
Total Annual Utility Savings: $2,031/year
Rear exterior of home after renovation
First (top) and second (bottom) floor plans
Building Enclosure
Roof: Unvented
Attic Insulation: R-60 with 4” rigid foam on the exterior and 5” high density sprayed polyurethane foam to the underside of the roof sheathing
Roof insulation: Two layers of 2” polyisocyanurate rigid insulation
Air Sealing: Airtight drywall approach; low expanding foam sealant around windows, sealants and adhesives used between framing components
Window Specifications: Double-glazed, Low-E, argon-filled: U=0.33, SHGC=0.33.
Wall Insulation: R-41 with blown cellulose cavity insulation and 4” of rigid foam on the exterior
Foundation: Conditioned basement
Foundation Wall Insulation: R-20 walls with 4” high density sprayed polyurethane foam
Slab Insulation: R-10; 2” XPS insulating sheathing under the slab
Drainage Plane: Taped foil-faced polyisocyanurate
Radon Protection: Passive system installed
Infiltration: 2.5 in2 leakage area per 100 ft2 envelope
High density sprayed polyurethane foam to the underside of the roof sheathing
Windows with exterior sheathing and furring strips
Four inches of exterior rigid insulation
R-20 foundation walls with 4" high density sprayed polyurethane foam insulation
Two inches of XPS insulating sheathing under the slab
Mechanical Design
Heating: 92% AFUE sealed combustion gas boiler in conditioned space
Cooling: 13 SEER split system in conditioned space
Ventilation: Supply-only system with outside air to return; run at low speed with an ECM motor
Filter: MERV 13
Return Pathways: Transfer grilles at bedrooms
Ducts: Sheet metal trunk and flex runouts in conditioned space
DHW: 0.8 EF side-arm storage tank
Appliances: ENERGY STAR dishwasher, refrigerator, range, clothes washer, clothes dryer
Lighting: Energy Star CFLs
Site Generated Power: 4.9 kW PV system
Sealed combustion gas boiler in conditioned space
Supply-only system with outside air to return
Additional Features
- Large overhangs with crown molding to accommodate additional exterior foam
- Front porch
- Maintenance-free fiber cement siding and trim
- Very high efficiency faucets, showerheads and toilets
- Plan minimizes water run-off from the site
