Monthly Archives: May 2010

What Goes On Underneath

At Historic New England each roof replacement is done in compliance with our preservation philosophy and our overall interpretation of the property.  Before starting conservation work at our sites, elements affected are researched regarding overall history, evolution, type of material, integrity, and any special features.  Conservation treatments are chosen that reflect a commitment to retaining and preserving historic material, which includes building changes over time as well as maintenance concerns.

The impending roof work at Beauport is no different.  The period of significance is interpreted at the late 1930s- following the original owner’s period of ownership (Henry Davis Sleeper- 1907-1934) through the second owner and their family’s period of ownership (Helena Woolworth McCann and Charles E.F. McCann 1935-1942).  Over the winter, the Property Care team researched and investigated several elements of the roof for better clarification of the present leaking issues as well as the overall built conditions.  Beauport’s roof was originally wood shingle.  In the 1940s, the roof was replaced with red asphalt shingles– not surprisingly, since the roof is over 20,000 square feet!  Following our own philosophy and the period of significance, Historic New England replaced the asphalt shingles back to wood shingle in the 1980s.  Now that the wood shingle roof is reaching its lifespan, new questions need to be answered… one of which is do we add underlayments and if so, which ones.   

Discussions continue regarding possible roofing underlayments— tar paper, felt, ventilation layers, waterproof membranes, etc.  New technology and ‘new and improved’ products provide a plethora of options when installing new roofs.  Some, however, can be extremely damaging to historic fabric.  We take the protection of historic fabric very seriously and sometimes double and triple protect vulnerable areas.  In other roof re-installations, we placed a bituthane layer on top of felt paper to allow for reversibility – an adhesive backed bituthane membrane will permanently bond to a wood substrate.  In this installation we specified the bituthane not in the traditional application, direct contact to sheathing with subsequent membranes and shingles applied on top, but rather as a self sealing membrane for any fastener penetrations that occur in an area that is a traditional point of failure on all roofs.

The specifications for the roof replacement in the 1980s state that the wood shingles were to be placed directly over wood sheathing.  In general, the current roof is in fair to good condition–most leaks can be traced back to flashing details and chimneys.  It was decided to review the current sheathing conditions to determine which underlayments (if any) are required for the roof.  The house is not heated, therefore there is not a history of ice dams but there is a long history with condensation issues. 

The team decided to investigate roofs that were built at different time periods—1908, 1912, 1917, and 1925.

Stay tuned…

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Filed under Roof Replacement