Monday, November 3, 2014

When the time is right: Appropriate use of modern materials in a traditional roof system

In my capacity as an historic preservation contractor and consultant, I am often afforded the opportunity to become involved in exciting and challenging projects.  Recently, we were awarded the contract to restore the clay tile roof turrets at the Longy School of Music’s Zabriskie House.  Now a part of Bard College, the Zabriskie House is actually the historic Edwin H. Abbot House with a sympathetically designed addition built in 1969-70.  The deteriorated condition of the turrets, as well as lead-coated copper gutter linings and masonry dormers, had attracted the attention of the Cambridge Historic Commission and a commitment to the proper restoration of these systems was struck between the CHC, building owner and a private donor.

Before I can specify historically appropriate treatments, I need to don my consultant’s cap and dig into the history of a building to best understand its evolution.  Developing the background story will typically answer questions and fill in the blanks when examining traditional building systems.  An 1890 newspaper clipping held by the CHC reports that “[t]he stately home of Mr. Abbot, with its walled-in grounds, on the site of the old Arsenal, promises to be the most costly private dwelling in the city.”  An examination of records held by the Massachusetts Historical Commission and from the Library of Congress’ Historic American Building Survey reveal that the firm of Longfellow, Alden and Harlow designed the Richardsonian Romanesque portion of the building and that Norcross Brothers was the builder of record.

Alexander Wadsworth Longfellow, Jr., was the nephew of the famous poet and an important figure in the architectural history of the United States. After graduating from Harvard in 1876, he studied architecture at the Massachusetts Institute of Technology and the École des Beaux-Arts in Paris, after which he worked as a senior draftsman in Henry Hobson Richardson's office.  After Richardson's death in 1886, Longfellow partnered with Frank Ellis Alden and Alfred Branch Harlow to found the firm of Longfellow, Alden & Harlow.  With offices in Boston and Pittsburgh, the firm designed many important buildings including the Carnegie Library of Pittsburgh and the City Hall in Cambridge, Massachusetts.

Norcross Brothers Contractors and Builders was a prominent nineteenth-century American construction company, especially noted for their work, mostly in stone, for the architectural firms of H.H. Richardson and McKim, Mead & White.  Following the death of Richardson, the brothers became the contractor for many of McKim, Mead & White's projects.  As had been the case with Richardson, much of the value of the Norcross Brothers to architectural firms derived from Orlando Norcross's engineering skill. Though largely self-taught, he had developed the skills needed to solve the vast engineering problems brought to him by his clients. For example, the size of the dome at the Rhode Island Capitol was expanded very late in the design process, perhaps even after construction had begun, so that it would be larger than the one just completed by Cass Gilbert for the Minnesota Capitol.

The Edwin Abbot House is an interesting interpretation of the Richardsonian Romanesque style.  Whereas the great majority of such buildings feature rusticated, pink Milford granite in an ashlar pattern, trimmed with East Longmeadow brownstone, Longfellow created a unique spin for Mr. Abbot.  While trimmed with the brownstone, the field of the walls features coursed Weymouth granite of slightly varying heights.  The motif of orange, brown and golden hues of the stone is continued in the brick wall surrounding the property.  The roof is covered in a flat, square orange-red clay tile.  This is typical of Richardsonian Romanesque buildings which are almost exclusively roofed in clay tile, Monson black slate, Granville, New York, red slate, or some combination thereof.  It should be noted that because their need for stone was outpacing the supply, Norcross Brothers eventually acquired their own quarries in Connecticut, Maine, Massachusetts, New York, and Georgia.

The roof framing system of steel and terra cotta blocks is relatively rare but makes perfect sense when considered in context with what the latest flooring technologies of the era were.  A network of steel beams was bolted together to form the rafters, hips and ridges of the frame. Across each was welded rows of double angle irons (or, inverted T beams.)  Within these channels, in beds of Portland cement, was laid the terra cotta block.  The tile were then fastened directly to the blocks with steel nails.  Because of the ferrous nature of the fasteners, the normal passage of moisture vapor caused the nails to rust and expand slightly, anchoring them securely in place.  Whether this element of the design was intentional or simply fortunate happenstance, the result made for a long-lasting roof.

What doesn’t last forever in traditional roofing systems like slate and clay tile is the sheet metal flashing assemblies.  Over the years there must have been numerous failures which lead to the decision to remove the clay tile from the broad fields of the roof and replace them with red asphalt shingles in the 1980’s.  Confronted with the dilemma of securing the new shingles to the terra cotta substrate, a decision was made to sheath the roof with plywood.  Holes were punched through the blocks and toggles used to fasten it to the roof.  In one area where the asphalt shingles were removed, more than 50% of the plywood exhibited varying degrees of rot due to the normal passage of moisture vapor from the interior spaces.

Fortunately, the turrets had survived the renovations from thirty years before.  A conical turret, in the rear, and an eight-sided hip-roofed turret on the north sided required only repairs which, while extensive, did not require addressing issues with the substrate.  The sixteen-sided turret, on the primary façade of the building, was in poor condition.  Over the years, “repairs” included the use of non-matching tiles, red roofing cement, tar, caulk, and even red slate.  A scaffold was erected to allow safe, unfettered access to the entire turret and the process of removing the tile began.  Care was taken to conserve as many tiles as possible for use in repairing the other two turrets.

The substrate was examined closely and, save for thousands of tiny craters created by the original nails, found to be sound.  A new system for fastening the tiles had to be devised so that they could be attached to the terra cotta blocks. It was critical that the new method allow for the replacement tiles to be securely fastened and resist the damaging forces of escaping moisture vapor.  Cement board, comprised of 90% Portland cement and ground sand, was fastened to the blocks with ceramic-coated masonry screws.  The entire turret was then covered with a self-adhering membrane.  The replacement tiles were carefully matched and sourced from a salvage dealer in Illinois and secured with stainless steel fasteners.  The flat tiles, no longer manufactured new, are referred to as “Cambridge” tiles for their prevalence on the roofs of great homes and institutional buildings in and around Cambridge, Massachusetts.

While I typically advocate for the retainage of all historic fabric when preserving and restoring traditional building systems, there are exceptions.  In the case of the Abbot House roof, we encountered once-modern technologies which pointed us toward contemporary means and methods.  Rusting steel nails in the terra cotta block worked brilliantly for the initial installation but seemed ill-conceived for a second go around.  The use of non-ferrous fasteners and a new substrate that is impervious to moisture infiltration will guarantee the turret’s service life for the next 125 years or more.
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Saturday, June 7, 2014

It's all about the money: How greed drives the "green" machine

Do you care about historic buildings?

Proposed changes to the International Energy Conservation Code threaten to cause irreparable harm to thousands of historic buildings in the United States.  I refer you to “International Code Council Approves Stringent New Requirements for Historical Structures” from Architect magazine ( 
If you don’t understand how contemporary insulation practices damage historic building fabric, please read “Is Greener Always Better?  Problematic Use of Modern Materials in Traditional Building Systems” (  According to the article referenced above:

“The changes, proposed by a team of industry representatives from the New Buildings Institute (NBI),the Natural Resources Defense Council (NRDC), and the Institute for Market Transformation strip the exemption language from the code. The group added a requirement that project teams file a report with a code official when seeking immunity on specific areas of the design or construction.” 
Who are these organizations that made this recommendation?

According to their website, the New Buildings Institute “is a nonprofit organization working to improve the energy performance of commercial buildings. We work collaboratively with commercial building market players—governments, utilities, energy efficiency advocates and building professionals—to remove barriers to energy efficiency, including promoting advanced design practices, improved technologies, public policies and programs that improve energy efficiency. We also develop and offer guidance to individuals and organizations on designing and constructing energy-efficient buildings through our Advanced Buildings® suite of tools and resources.” 
I didn’t see anything that indicates an understanding of traditional building systems so I checked out the Natural Resources Defense Council’s website.  Still nothing about old buildings.  They’re an environmental action group whose mission statement is “to safeguard the Earth: its people, its plants and animals and the natural systems on which all life depends.”   Admirable, but where’s the expertise determining what’s right or wrong with energy conservation relative to older building stock?

That left just the Institute for Market Transformation … would they be the ones with demonstrable knowledge and expertise relative to traditional building systems?  According to the website, they’re “a Washington, DC-based nonprofit organization promoting energy efficiency, green building and environmental protection in the United States and abroad. IMT's work addresses market failures that inhibit investment in energy efficiency and sustainability in the building sector.”  Lobbyists in DC!  If historic buildings are exempt from the IECC, this special interest group’s sponsor/members can’t make any money selling the materials that the proposed code changes will require.
Like so many things, this has nothing to do with right or wrong: it’s about big businesses making money.  The Codes Council appointed three organizations who know nothing about how green building practices will adversely impact traditional building systems and destroy historic fabric.  Why wasn’t the Association for Preservation Technology or a similar entity included?  Why?  Because the Council doesn’t want to hear what they have to say.  Under the guise of energy conservation, those who profit from “green” building practices are determined to cut into the historic restoration market.  The end result will be the catastrophic loss of centuries-old buildings.  What do they care?  The ruined, old buildings will be razed and a “green” one can take its place.  Consider this quote from the article:

“In Boston, for example, more than 8,000 properties are either located in one of the city’s nine Historic Districts or are designated as a local landmark, according to the Boston Landmarks Commission. For Manhattan alone, New York’s Landmarks Preservation Commission lists 65 historic districts; Kerr adds that approximately a quarter of all lots in that borough are landmarked.”
Implementation of IECC 2015, in the proposed form, will be disastrous.  I implore everyone reading this to spread the word.  Will the NTHP, MHC and other state SHPO’s lead the charge against elimination of the preservation exemption?  Perhaps, but we must all be leaders and cannot rely on others to advocate against this change.  This is our fight and the time is now.

Thursday, June 5, 2014

Is Greener Always Better? Problematic Use of Modern Materials in Traditional Building Systems

When new words and terminology enter our vernacular, they often take on a connotation larger and broader than they deserve.  Today, “green” and “sustainable” are synonymous with responsible living and construction, their meanings understood as clearly by an architect or engineer as they are by the lay person.  They are buzz words that make consumers feel good about their purchases; they’re doing their part to protect the environment and help save the world.  But, in certain applications, use of these terms is more than a misnomer; it’s outright false advertising.

Technological advances in building science have allowed for the creation of the most energy efficient systems and materials that the construction industry has ever seen.  With the ever rising cost of every fuel type, energy conservation is always a high priority when planning for and designing buildings.  Buildings, historically, are only as efficient as the technology of the day allowed.  While we may shudder with the chill of a stiff breeze standing by the window in an 1885 Queen Anne Victorian, imagine the relative level of comfort that one of the Pilgrims would have enjoyed in the same situation!

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.