Friday, August 21, 2015

A More Resilient Fowler Clark: Preparing a Historic Farmhouse for Climate Change

Photo: HBI 201412
Photo: HBI 201412
Boston architect Susan Pranger has been blogging with HBI over the last month with focus on climate change and its effects on the maintenance and materials of historic buildings.  The buildings at HBI’s prospective project at 1786 Fowler Clark Farm in Mattapan were among those Susan used in her capstone project at the Boston Architectural College to model some of her recommendations for preparing historic structures to withstand the impacts of new weather associated with temperature changes.

The biggest threat from climate change to buildings like the historic Fowler Clark Epstein Farm is the projected increase in rain and humidity, aggravated by higher winds, temperature and UVB rays.  After discussing how climate change will threaten wood structures, the question remains:  What can we do to make historic buildings more durable in the face of climate change?

While Fowler Clark Epstein is unlikely to be threatened by sea-level rise, it is at risk of local flooding caused by rain events that will be more severe, more frequent and of longer duration. Although the farmhouse sits at the high point of the farm, the ground at the perimeter of the building is near the first floor framing and wood shingles. Preventive action is required, first to clear debris and extend downspouts away from the perimeter, and second, to regrade to collect and direct storm water away from the building.

Projected increases in rain and UVB will combine to increase the rate of weathering of exposed wood. Because the existing unpainted cedar shake at Fowler Clark Epstein are already badly deteriorated, there is an opportunity to replace them with more robust and weather resistant materials.

Pranger 2015
Pranger 2015
The wood trim on Fowler Clark Epstein may be original but a section of exterior wall, hidden within a later addition, suggests that wood clapboards existed on the farmhouse before the existing cedar shakes. Both cedar shakes and clapboards were popular in the 18th century, and would have been hand riven (cut) and smoothed, a process that reduces the extent of open grain and makes riven products resistant to excess water absorption. Unpainted wood also has a natural tendency to swell in response to initial rain exposure, preventing subsequent rainwater from entering through cracks and joints. However contemporary saw milled products expose the end grain, are less moisture resistant, and are less capable of resisting saturation during long rain events. This suggests a paint or stain finish should be considered for all exposed new wood materials. Painted clapboard would be both authentic and more resistant to wind, rain and sun.

Of course “the devil is in the details” and the exterior materials are only as good as the workmanship. Building orientation and effective overhangs influence the extent of weathering on exterior walls. It may be possible to improve the effectiveness of the drip edge of the overhang while maintaining its historic appearance. At a minimum the eaves and overhangs should be restored to a weather tight condition. Similarly, restoring the lintel caps will can protect the doors and windows.

In New England, humidity is predicted to increase along with average temperatures, creating conditions that can contribute to the spread and growth of mold, fungi and insects. If the powder post damage in Fowler Clark Epstein is recent, it may be necessary to fumigate the house, as pesticides and preventive coatings would only be effective if they reached all surfaces of the timber framing.

Efforts to control the migration of humidity and water vapor is a complex endeavor that must consider the impact on building materials, occupants and contents. Changes in exterior and interior conditions should be monitored during daily and seasonal swings and over time. However the overall good condition of this 200 year old farm house indicates that it was well built and will respond well to renewed care and attention.
Cropped from HBI photo 2014
Cropped from HBI photo 2014

Bob Vila, “Old House Restoration, Clapboards” Popular Mechanics, December 1990, p.74, 76.
Michael F. Potter “ENTFact 616 Powder Post Beetles” UK Entomology
Jan Carmeliet and Bert Blocken. “Rainwater Runoff for Evaluating Water Leakage Risks in Building Envelopes” Oak Ridge National Laboratory http://web.ornl.gove/sci/buildings/2012/2004%20B9%20papers/196_Carmeliet.pdf.

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