This home was purchased and retrofitted with additional square footage prior to the new owners moving in. Data from local electric and gas companies using their regional average usage costs was used as a baseline. We believe the energy reduction is greater than the calculations reflect, but since no quantified data was available, a conservative approach was taken.
Sealing and insulating the building envelope is the key to lowering energy demand. Two choices were available in approaching this task: insulate the building on the outside of the existing walls, or insulate it on the inside. In this case, the latter approach made the most sense.
The owners chose to keep intact the original stone veneer, and insulating the basement walls from the interior was far more economical. Roughly 40% of heat loss and gain in existing buildings is due to air infiltration. Open cell and closed-cell polyurethane foams excel in retrofits because they seal buildings so well against air infiltration. In new construction, there are less expensive and less fossil-intensive ways to seal and insulate, and these methods were preferred over the foams in those cases. But when it comes to retrofits, nothing is so effective at sealing a building as the spray foams.
GEM Disclaimer: We were unable to quantify the energy reduction based on prior usage because the previous owner‘s utility bills were not available. However, average usage for the square footage and region supplied by the utility companies gave an energy reduction of 60% electric and 30% gas. The average utility savings were quantified by average regional and square footages typical for this area, and baseline calculations totaled $1,341 yearly cost reduction for this property.
Energy related design decisions:
- Continuous 3‘ overhang at new south-facing sunroom and at kitchen addition for summer solar protection.
- Natural light to all living spaces to avoid artificial lighting during daylight hours.
- Energy envelope upgrades.
- Walls: Existing exterior masonry walls: closed cell foam insulation to R13.
- New exterior wood frame walls: open cell foam insulation to R13/R22.
- Roof: Open cell foam insulation between joists to R-38.
- Relatively high reflectivity roof shingles for lower summer solar heat gain.
- Double-glazed, triple-glazed argon filled wood windows, with muntins
- Breakfast floor slab: foam between sleepers to R-20.
- Properly sized all-sheet metal (no flex) ducts; Mastic duct sealing.
- Insulated hot water and refrigerant lines.
- Energy recovery ventilation system by American Aldes. 2 units.
- SEER 15 AC system. Variable speed motors for modulation to actual cooling load.
- Burnham 206 boiler provides hot water to radiant flooring, and to coils in ventilation
(hydro-air) system, and domestic hot water. Size: less than Â½ the size of original
boiler in the home.
- Wirsbo radiant flooring in new breakfast room; Programmable zoned control system.
- EnergyStar ceiling fans circulate air and allow raising set points for thermostats.
- Dishwasher, refrigerator and clothes washer are all EnergyStar rated; Aquia Dual
- MBA – Hansgrohe Croma E Green 3-jet showerheads, 1.75 GPM.
- Compact fluorescent lighting in decorative fixtures; LED downlighting; Halogen lighting
MasterSet central lighting control system.
Energy Efficiency Case Study Data
|PROPERTY CITY, STATE||Arlington, VA|
|COST OF CONSTRUCTION||$ 250,000||Square footage 800 sq ft addition included|
|COST OF LAND||N/A|
|EXISTING PROPERTY VALUE||$ 1,100,000|
|COST OF UPGRADES||$ 75,000||Green measures (see list of upgrades)|
|TAX CREDITS, REBATES||N/A||Have not applied for tax rebates yet|
|Utility (Elec) kWh rate||$ 0.11|
|Monthly utility savings||$ 111.75|
|Yearly utility savings||$ 1,341||Electricity & Gas|
||Usage (kWh)||Electric Bill||Therm Usage
|March||1406||$ 139.11||81||$ 99.06|
|April||1209||$ 123.97||59||$ 72.88|
|May||1216||$ 124.69||21||$ 34.42|
|June||1531||$ 171.68||16||$ 28.82|
|July||1832||$ 213.06||17||$ 29.04|
|August||1591||$ 186.06||16||$ 29.88|
|September||1263||$ 151.70||14||$ 25.60|
|October||1110||$ 124.93||16||$ 29.93|
|November||1531||$ 163.74||73||$ 89.74|
|December||1350||$ 147.32||94||$ 118.62|
|January||1406||$ 150.38||152||$ 171.19|
|February||1313||$ 108.87||118||$ 130.78|
|TOTAL||$ 1,805.51||$ 859.96|
|Baseline Reductions||$ 1,083.31||$ 257.99|
|Formula 1, PV||$ 16,712|
|Formula 2, SQ Ft * $20||$ 26,820|
|INCREMENTAL PROP VALUE||$ 21,766|
|Total Upgrade Investment||$ 75,000|
|NEW PROPERTY VALUE|
|*GEM Payback Method||N/A|
|FUTURE VALUE (FV)||$ 44,341||@ 5%, 20 years|
|Owner renovated, added 800 sq ft high end property, no baselines were available|
|Assumption is an energy reduction well above 50%, 25% conservative calculation used|
|**GEM Payback Method includes extra energy savings pmt + Bi-
|Utility prices expected increases of 30% in next 5 years not used in calculation|