Historic Preservation vs. Energy Efficiency: And the Winner is…
By Andrew P. Borgese
On one hand is historic preservation and on the other is energy efficiency, and never the twain shall meet. At least, that’s what recent history has taught us. Purists who believe that altering any part of an historic building is sacrilegious, and fervent energy conservationists who believe that reducing energy consumption should take precedence over all else, are rarely able to agree. However, upon closer observation, we can see that there is, in fact, common ground. Both groups are passionate in their desire to sustain existing buildings and extend their useful life for as long as possible. Recognizing this fact, we embarked on a design process focused on integrating preservation goals with energy efficiency goals in a way that creates a symbiotic rather than a mutually exclusive relationship between the two. The historic rehabilitation of the WCAI radio station in Woods Hole, MA (a local NPR station and affiliate of WGBH Boston) is a case in point.
This classic Greek revival structure built in 1842 by a local mariner had many owners over the years and prior to our involvement was clad with asbestos shingle siding, had a failing asphalt roof, was under- or un-insulated at exterior walls and roof, and much of the existing trim at corner boards, rakes and fascias was warped and cupped and pulling away from the structure. Cheap repairs to this trim and to the two brick chimneys over the years had also shown signs of failure. Many existing double hung wood windows still remained but were in poor condition.
In 2009 WGBH purchased the building in which their WCAI affiliate had been a tenant for the previous 10 years and decided to invest in their new acquisition for the purpose of preserving its value and increasing its usefulness. The necessary repairs were extensive enough that they required much of the building to comply with current building codes including structural, life safety, energy efficiency, and handicap accessibility issues. The building’s location within an historic district also required that the design be approved by the local Historic Districts Commission with respect to any work on the exterior of the building. Longevity, low maintenance, and operating efficiency were among the key concerns for this renovation project.
The entire exterior skin of the building was in need of repair and the Owner was able to receive a substantial grant from the town as long as this exterior work was done in accordance with the Secretary of the Interior’s Standards for Historic Rehabilitation. As layers of cladding and roofing materials were removed, some were set aside for reuse while others were beyond repair or not original to the structure and discarded. Once the original board sheathing was exposed on the walls and roof, it was revealed that there was no insulation in these cavities so we proceeded to fill them from the exterior with dense packed cellulose insulation with Tyvek Housewrap stapled on the outside face of the boards to prevent spillage of the cellulose between boards. This took us from an R-value of about 1 to an R-value of 18 between studs (studs were 4 ¾” actual thickness) and about the same between rafters (rafters were 4 ⅝” actual thickness). After that, a layer of 2” foil-faced polyisocyanurate foam insulation was installed on all exterior wall and roof surfaces effectively wrapping the building with R-13 insulation and eliminating almost all thermal bridging. The seams between the foil-faced foam sheets were all taped with foil tape completing the wind and air barrier portion of the wall assembly. Vertical strapping was then installed over the foil-faced foam with 5” pan head spider drive screws into each stud. Additional 1x material was installed over the foam at window and door heads and sides as nailers for trim and siding materials. New red cedar beveled siding was then attached with stainless steel ring shank nails to the vertical strapping. At the bottom and top of the walls, between the columns of strapping, a strip of Cor-A-Vent was inserted for two specific purposes. First, it allowed for a vented ¾” air space behind the clapboards which will allow them to dry after high moisture weather events. Second, it completes our rain screen wall in which any water that gets behind the siding will be stopped at the foil-faced insulation panel and drain down to the bottom of the wall and out through the screened Cor-A-Vent. While the exterior foam adds to the construction cost, the benefits of increased R-value, elimination of thermal bridges, and vented rain screen design are substantial and measurable in terms of indoor air quality and comfort, building durability and longevity, and reduced operating costs for heating and cooling throughout the life of the building.
On the roof we installed 5/8” Zip Board sheathing over the foil-faced foam using the same pan head spider drive screws as we used on the walls. As per the manufacturer’s instructions for this product, all seams were taped with their acrylic adhesive Zip System tape in order to provide what they claim to be an air tight, water tight seal. The reason for a full layer of sheathing on the roof rather than the strapping as we had done on the walls was to provide a continuous nail base for the new red cedar roof which was installed over a layer of “Cedar Breather” which provided a drainage plane and a vented air space below the shingles.
Any portions of exterior trim that were salvageable were repaired and reused. In all other instances, profiles were reproduced from sections of moldings that were removed and from archive photographs of the original structure provided to us by the Woods Hole Historical Collection and Museum. Although much of the original trim was cypress, all new wood used for the exterior trim was red cedar. This decision was heavily influenced by cost and although it constituted a change in material it was consistent with the requirements for an historic rehabilitation.
Windows often seem to be the focus of much of the discussion on preservation vs. energy efficiency. In this case, all windows that were determined to be original were removed, completely restored and reinstalled. All other windows were replaced with new wood double hung windows to match the original windows in style, size and muntin pattern. Once reinstalled, the restored windows were much more air tight, and even though the sashes were single glazed, the addition of interior storm panels will significantly improve the overall window R-value.
Due to the nature of this building being used as a radio station, there is a large amount of electrical equipment, devices and instruments housed throughout the three floors which give off a tremendous amount of heat all year round so there is a greater demand for cooling than there is for heating. Since the budget did not allow for the entire mechanical system to be replaced and upgraded, we focused on the condensers for the air conditioning system. Three existing condensers with single speed motors and SEER ratings of 10 were replaced with three higher efficiency 15 SEER units with ECM motors. Ductwork was extended to provide cooling to the only office that did not have central air conditioning and a 20 SEER Daikin heat pump with three heads was installed to serve the newly renovated lower level.
The basement or lower level of this building was uninhabitable at the beginning of this project and the goal was to create a small meeting space that could be opened to the public. This meant that the new space would need to be handicap accessible and have an accessible restroom. The existing interior stairway was about 30” wide with tight winders, 10” risers, 7” treads and nowhere near code compliant so we designed a new stairway connecting the lower, middle and upper floors which involved some reconfiguring of spaces on each level. However, there was no room for an elevator shaft within the existing building footprint, and the site was too constricted by required parking spaces, property lines and zoning setbacks that an elevator tower on the exterior was not feasible either. The solution was to provide an accessible route from the parking area to a restored exterior door to the lower level which had been boarded up for decades. This series of ramp, stairs and chair lift was designed to blend with the existing topography of the site and the railings embellished with the same simple architectural elements found on the existing building.
The interior of this basement space which is fully below grade on one side and a walk-out on the other has a large granite block foundation for about two thirds of the exterior walls and wood studs for the rest. The existing wood floor was framed directly on dirt and rubble fill and was not salvageable. After removing the existing floor system and a couple of inches of earth and rubble, 2” thick sheets of XPS foam insulation were installed on grade and a new concrete slab poured. New perimeter stud walls were constructed on top of the slab in front of the granite block foundation walls and open cell spray foam was sprayed against the granite and flush with the inside face of the studs filling the cavities completely. Open cell spray foam was chosen for this particular location because of its void-filling capacity against the joints of the stone masonry wall; its exceptional performance as an air barrier; its lower odor and water based blowing agent (as compared to closed cell foams which use hydrofluorocarbons); and its ability to provide a thermal break between interior and exterior surfaces.
The last element of this historic rehabilitation was the addition of a narrow deck at the middle level which we discovered by perusing historical photographs which also included images of a formal entry door with an elaborate architrave. The redesign of these features was based primarily on studying the archive photos and researching similar details on contemporaneous buildings. Although the deck and stair layout needed to be modified slightly from the original due to public land takings and property line changes over the course of 170 years, the end result is generally consistent in scale, size, materials and intent with the original construction. In order to illuminate the egress stairs down to grade, LED lights were concealed in the bottom rails so they were not visible to the general public and we did not have to introduce another light fixture on the building that would be a departure from its original appearance.
From an historic preservationist perspective, we have ended up with a building that is architecturally and historically accurate and generally consistent with the building’s original design and materials. Original materials were reused wherever possible, and when this was not practical, were replaced with the same or similar materials. Original windows were saved and restored. Original design features (deck, doors) were reconstructed and put back into service. Historical research guided the color selections for the exterior siding, trim, windows, shutters and wood doors. Today, this building looks more like it did in 1842 than it has in generations.
On the performance side, we have insulated a previously un-insulated building to exceed today’s energy code requirements. The building envelope has been dramatically improved by eliminating thermal bridges and an extremely effective air barrier was provided thereby reducing the loss of conditioned indoor air. An exterior drainage plane, or vented rain screen, is now a permanent part of the wall assembly which will manage water by effectively diverting it away from structural and cladding components. We know that water is the single greatest cause of damage to buildings. This detail alone can be critical in perhaps doubling or tripling the useful life of the components in this wall assembly. A blower door test conducted before renovation work yielded a measurement of 7,867 CFM at 50 Pa and 0.94 ACHn compared to our post-renovation measurement of 2,760 CFM at 50 Pa and 0.33ACHn. In simpler terms, this means that the air leakage from the building measured in cubic feet per minute (CFM) and tested at a pressure of 50 Pascals was reduced by 5,107 CFM. Another way of analyzing this data is to look at the natural air changes per hour, or ACHn. Air changes per hour is a measure of how many times the air within a defined space (in this case, the entire building) is replaced. Prior to our work, we measured a rate of 0.94 ACHn which means that almost the entire volume of air in the building is being replaced through leaks in the building envelope. Post-renovation measurement show the ACHn was reduced to a third (0.33) of what is was originally. In this building, that amounts to about 19,000 cubic feet of heated or cooled air every hour that is no longer leaking from the building. We expect that this dramatic difference between pre- and post-construction air-tightness measurements will be evidenced by a significant reduction in operating costs.
We have learned from this project that by identifying the common goals from both the energy efficiency and the preservationist perspectives, and arriving at compromises that positively impact a building’s sustainability, durability and longevity, we can achieve results that satisfy both agendas through holistic and long lasting solutions.
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