Energy Upgrade in Sommerville, Massachusetts

This is a energy retrofit of a two family Victorian located in a historic district. While historic districts can be quaint, they can also be difficult places for energy retrofits. The enclosure was difficult to upgrade because we weren’t allowed to remove siding or replace windows. We converted the over/under configuration to side by side units and brought the attic into the conditioned space to boost living space. One side is the current home of Building Science Corporation; the other is a rental unit. The basement was made into a warm dry storage area for our massive book inventory. Energy consumption was cut by 50%.

STEPS TOWARDS ZERO ENERGY:
1. Upgrade the mechanicals:

• Furnace: Replace 60% efficient boiler (200,000 Btu) with a two smaller Hydro-air systems. A sealed combustion condensing gas boiler (80,000 Btu, 90% efficient) with water tank (SuperStor Ultra) and a condensing hot water heater (90,000 Btu, 85% efficient) make domestic hot water and provide space heating.
• AC: Window units replaced with direct expansion units (14 SEER) placed on pads in the yard. Energy efficient low sone exhaust fans in all bathrooms, fully ducted exhaust fan over kitchen stove

2. Bring the basement inside the house.

• Drainage mat over existing concrete floor, 2 in. extruded polystyrene (XPS) insulation, topped with a 3 in. concrete slab.
• Sill timbers were lifted off of the brick walls and separated with a capillary break (roofing membrane). 2 in. closed cell foam sprayed to the inside of the foundation and then separated from the interior space with a thermal barrier as required by the building code. In this case, a 1 5/8 in. metal stud wall provides support for paperless drywall (DensGlass gold, www.gp.com).

3. Super insulate and air-seal the roof (R-50)

• Insulation removed between second floor and attic.
• Top plate connected to attic rafters and closed with building paper.
• To adequately support the load of the slate roof, we had to increase the rafters from 2x8 to 2x12. We filled these deep cavities with less expensive open cell foam (www.Icynene.com) (R-40).
• 2 in. XPS below rafters (R-10) provided extra insulation as well as vapor diffusion resistance.

4. Upgrade Windows. We replaced 1/3 of the windows with tilt-in replacement windows. The balance was done with replacement sashes into the existing frames (see materials notes below).

5. Insulated walls. We were able to remove siding to spray in low density open cell foam in 1/3 of the wall area, the remainder of the walls are still uninsulated (see materials notes below).

6. Energy Star (or better) fixtures and appliances

• Energy Star refrigerators (GE and KitchenAide), dish washers (Bosch), and stacking washer/dryers (GE).
• 60% of the light fixtures used were pin based Compact Fluorescent fixtures. The others were period fixtures and were fitted with screw in CFL bulbs.

SPECS:
Completed: 2003
Bedrooms: 4 before, 4 after
Bathrooms: 2 before, 4-1/2 after
Cost of renovation: $125 per sq. ft.
Conditioned space: 2,150 before, 2750 after plus 1,000 sq. ft. of dry warm basement storage.
Annual utility cost: Gas $3,600 before; $1,474 after;Electric $1,200 before; $830 after

MATERIAL NOTES:
Because the roof was covered in slate and the historic commission wanted it to stay in place, all insulation had to be from the roof deck towards the inside. We used open cell foam because the rafters were 12 in. deep; this coupled with 2 in. of XPS on the underside gave us sufficient overall R-value (R-50).

Because the house is in a historic district, we were severely limited in our insulation strategies. On one side we were allowed to remove siding, install house wrap, blow in open cell foam insulation, and replace the siding. On all other sides, we were not allowed to remove the siding in order to tighten up the wall sheathing. For this reason, we were unable to blow in any type of insulation.

The Historic commission allowed us to replace the window frames in the locations where the siding needed to be replaced. All other windows were fitted with new double glazed low e sash. This didn’t improve performance much because the openings were not perfectly square. New windows are double glazed, low-e (www.marvin.com).

Old solid wood doors were salvaged and weather-stripped; some were replaced with energy efficient doors featuring double glazed, low-e lights (www.thermatrue.com).
WHAT WOULD WE DO DIFFERENTLY?
Historic commisions and committees all over the country have interest in windows, chimneys, roof finishes and siding that often conflict with best practice where long term durability of the structure and its energy efficiency are concerned. We compromised and used all wood simulated divided light replacement sashes from Marvin for 2/3 of the window units. Because the openings were so far out of square, the sashes never fit right, and had to be fussed with more than we had expected. We were also not prepared for the battle regarding the siding replacement, and left it until a future phase. It is our intention to go back and replace the balance of the siding, and when we do that, we will blow cellulose into the remaining 2/3 of the wall cavities, and will add insulation sheathing at that time as well. We will brace ourselves for the dialog with the historic committee.