Today’s building designers want to create watertight, airtight structures that use minimal amounts of energy with windows sealed tight and year-round climate control for maximum comfort. They strive to design an envelope that needs low or no maintenance, fully accepting that building owners will not care for their buildings as a given. As far as new construction goes, there’s no problem. In fact, this is good news. But what happens when the owners of older buildings want to implement these new technologies to increase the efficiency of their buildings?
Older building stock tends to be far less efficient than modern buildings. Wall systems and joinery, windows and doors—they’re just not as tight. An unexpected benefit of these inefficiencies is the passive ventilation that occurs, be it laterally through windows, doors and walls, or by the “stack effect” in which warm air rises, bringing vapor with it, escaping through the uninsulated roof system. Know this: older buildings breath. Modern building systems are designed so that structures don’t breath and vapor is removed with dehumidifiers or other mechanical forms of ventilation.
In older buildings, solid masonry walls rely on the temperature gradient between interior conditioned spaces and the outside for walls to drain properly. Insulating these walls stops or mitigates the passage heat through the solid brick masonry. This slows the drainage/drying process and traps moisture vapor in the wall which, during freeze-thaw cycles, freezes and expands up to 12% in volume. Oftentimes the result is damage to the wall system of the envelope. Instead, the focus should be on controlling moisture and preventing it from entering the wall system, both inside and out.
Today, older buildings have kitchens, bathrooms and laundry spaces that they didn’t when first built. This introduces a significant amount of moisture vapor that may enter the wall system from the interior. Installation of a vapor barrier will prevent this from occurring without impacting the thermal effect that heated interior spaces have on the exterior walls. Outside, mortar joints must be kept tight and full. Penetrations such as window and door jambs must be sealed tight where they abut masonry to prevent water intrusion.
Roof drainage systems must be functional; gutters protect and shed the walls from runoff and properly placed leaders direct the rainwater away from the building at grade. It’s also interesting to note that many older masonry buildings have large windows resulting in a high window opening-to-wall surface area ratio. Improving the efficiency of the fenestration through conservation and repair, as well as the addition of efficient interior or exterior storm windows, will help preserve the historic integrity of the building while also saving on energy costs.
Recently a client contacted me with questions and concerns about insulating his masonry walls. He was engaged in gutting much of the interior space in his circa 1870 brick townhouse in a National Register historic district in Boston’s South End. The building department was demanding that he insulate behind the walls in compliance with the International Energy Conservation Code. When we pointed out that the code specifically exempts buildings on or eligible for inclusion on state or national historic registers, he said it didn’t matter if there was a lot of interior gutting; that was his interpretation of the code. Only later, when a staff member from the Boston Landmarks Commission intervened, was he straightened out.
Before you breath a sigh of relief, owners may have to prove that their historic projects are worthy of exemptions from the International Energy Conservation Code following changes to the forthcoming 2015 version approved by the International Code Council last year. The changes were proposed by representatives from the New Buildings Institute, the Natural Resources Defense Council and the Institute for Market Transformation and they remove the exemption language from the code. The group added a requirement that permit applicants file a report with a code official when seeking immunity on specific areas of their project.
Do they sound like groups that know about old buildings? No, they don’t. They sound like groups that think LEED certification matters when it comes to old buildings; you know, organizations that don’t think full life cycle analysis matters in “green” building practices. Why wouldn’t the team include representatives from the Association for Preservation Technology or the Preservation Trades Network? And, frighteningly, who will train the code official that decides whether a project receives an exemption or not? The answer is NOBODY. So guess what happens when you encounter our friend in Boston?
More and more I’m coming to believe that these people actually hate old buildings. I’ve had arguments with architects and contractors who wanted to spray closed-cell foam insulation between the rafters under slate roofs. Some specified removing all the slate and covering the roof with an ice and water shield membrane then reinstalling the slate, effectively “sealing” the roof tight. Besides being an unnecessary, exorbitant extra cost, there’s a big problem with these grand, USGBC-inspired plans: they actually destroy the materials in a traditional roofing system.
Slate, clay tiles and wood shingles are traditionally fastened to battens, skip sheathing or regular old boards—not plywood, no underlayments. The roofs are water tight, not air tight and the building breaths through the roof. Fiberglass insulation can improve energy efficiency and reduce heat loss without preventing the roof from breathing. Additionally, soffit and ridge ventilation can be added if desired. Traditional roof materials like slate, clay tile and cedar shingles experience condensation. The passage of vapor helps dry things out. When you stop the roof from breathing everything stays wet.
Slate is comprised of thin layers of metamorphic rock that delaminate and fall apart when they are kept damp for months. Clay tiles, like terra cotta and brick, will disintegrate. Wood shingles rot. Steel fasteners will experience corrosion and fail. This has been the end of many a slate roof; I’ve pulled the slates off the roof and seen it with my own eyes. Cedar shingle roofs will last five years, max, when installed on a solid roof deck covered in ice and water shield. The reality is this: greener is not always better, especially when wielded by those unfamiliar with traditional building systems. “The greenest building is the one already there” is a common expression in the historic preservation world yet it’s never heard in “green building” circles. Go figure.