Renovations of older, distressed homes throughout the city of Cleveland are meeting improved green standards because of incentive programs and funding opportunities that encourage better building. But what will it take for existing homes to achieve more dramatic energy reductions in line with evolving energy codes and standards? Can we achieve deep energy reductions cost-effectively in affordable housing? We wanted to find out.
Over the past two years at Environmental Health Watch (EHW), we managed a HUD-funded technical study of green retrofits of 12 affordable homes.
Six of the houses were upgraded to EHW’s deep energy retrofit (DER) specs to achieve at least 70% energy-use reductions. The other six were renovated to Cleveland’s “Green Building Standard,” which included affordable green housing standards established by Enterprise Community Partners (greencommunitiesonline.org) and energy-efficiency standards set by Energy Star v.2. We are monitoring energy usage (actual vs. predicted) and indoor air quality (IAQ) in all 12 homes.
This HUD technical study has two purposes: 1) to compare the effects on indoor air quality of deep energy retrofits and Energy Star v.2 retrofits, and 2) to determine the costs and benefits of deep energy retrofits for affordable housing. We are in the data-collection phase of the study now. The construction work is complete, so we can share our experience with implementing the DERs and our thoughts on the challenges and opportunities presented by these types of retrofits.
The homes were developed by a nonprofit community development organization, Cleveland Housing Network (CHN), for lease-purchase to low-income residents. Other partners in the project included the Swetland Center for Environmental Health at Case Western Reserve University’s School of Medicine, and Intwine Connect, a Northeast Ohio tech company.
Some of the key improvements made to these houses include tighter building enclosures, better windows and doors, more efficient mechanical systems, energy-efficient lighting and appliances, energy recovery ventilation, and increased insulation (see illustration, pages 58 and 59).
Although our deep energy retrofits added almost $26,000 to what was already an expensive gut renovation, this kind of investment is necessary to dramatically alter energy usage. We think the extra effort is justified because high-performance houses can save occupants money and improve comfort and indoor air quality while reducing C02 emissions. DER specs are extreme compared to today’s building requirements, but they are in line with proposed future energy codes. And the price will continue to fall as these features become more common practice.
Upgrading the Building Envelope
The six Energy Star houses received well-executed dense-pack cellulose (R-13) blown into wall cavities, and attics were insulated above code levels (R-38 to R-50). Air-sealing was also above average, with final blower-door test-out numbers averaging 1,658 at cfm50 or 6.46 ACH50, which is considered to be in the mid-range for older, renovated homes. Across the six Energy Star houses, numbers ranged from 3.17 to 9.42 ACH50, while HERS scores ranged from 67 to 80, with an average of 71 (see “Measured Performance,” page 60).
The six DER houses received substantial insulation upgrades. Rigid foam board was applied to the exterior in two layers (3 inches total) so that seams could be staggered. When done properly, this upgrade drastically improves airtightness, thermal resistance, and durability all at once. Cavity insulation is a great start, but doesn’t eliminate thermal bridging — the framing makes up 25% to 35% of a cavity wall, creating thermal weak spots that readily conduct heat to the exterior. Without a good exterior air barrier (the foam board in this case), it is very difficult in an old house to improve air-sealing beyond what was achieved in the Energy Star homes (6.46 ACH50 on average).
The added attention to air-sealing and insulation details (including the basement and attic) in the DER homes achieved an average blower-door test result of 623 at cfm50, or 2.15 ACH50. The numbers ranged from 1.61 to 2.75 ACH50, while HERS scores ranged from 34 to 44, with an average of 38.
Attic. The accessible attic spaces in all six of the DER houses were abandoned, which made it easier to air-seal and insulate to R-60. Storage access was discouraged by removing attic staircases in exchange for tightly sealed attic hatches. No mechanical equipment or ductwork was allowed in these spaces. In some Energy Star houses, the attic staircases were left in place and the stairwells insulated, with a platform provided for storage.
In most of the houses, the attic floors had tongue-and-groove flooring over 2x4 or 2x6 second-floor ceiling joists. Once the second-floor ceiling was drywalled, the ceiling joist bays were dense-packed, creating a pretty good air-seal. More insulation was then blown over the top of the floor (up to R-50 in Energy Star houses, and up to R-60 in the DER houses).
Basement. In a DER renovation, basement details are treated with much greater attention than they are in a typical renovation. Controlling below-slab soil gases, moisture, and thermal losses becomes a necessary upgrade to avoid aggravating these problems in a tight house. Much can be accomplished through perfect air-sealing and insulating, though radon has proved able to bypass even the tightest of assemblies (justifying the expense for below-slab passive radon exhaust systems).
In the case of our six DERs, the existing slabs were torn out so that we could make things right from the ground up. Due to the quality and benefit of the added control layers, it was considered to be worth the added cost.
Upgrading Doors and Windows
For this upgrade spec, we asked our existing suppliers for suggestions on how to achieve the lowest U-factor at the most reasonable price that they could provide. In the DER houses, we ended up with affordable Alside vinyl windows with U-factors between 0.18 and 0.22.
In many cases, we were able to reduce the number of windows to help pay for the better units. North-facing windows were avoided or eliminated when there were more than necessary. Some three-window bay sections were removed and replaced with a flush wall and two upgraded casements, which resulted in easier thermal detailing and reduced heat loss.
The added foam (and double studs in two cases) created extra- thick walls that raised a question about where to locate the windows: flush with the outside edge (“outie”) or the inside edge (“innie”). While I favor the innie for performance and protection from the elements, the outie costs less because it is very straightforward to install, and more in line with standard practices. We ended up using both approaches.
We specified R-7 doors with thermally broken door frames, but due to timing and availability not all the houses got this upgrade.
