There is a substantial layer of plaster between the shingles and the roof sheathing. This is something that Mr. Van Lieu had never seen in sixty years in the building business, with a great deal of time spent in old buildings. He offers two possibilities: It could be a layer to prevent air infiltration much like tar paper, or, it could be an attempt to make the building fire resistant. An interesting idea given the Church's narrow escape from the Great Fire. According to local history, noted astronomer Maria Mitchell barred the way to local officials who intended to blow up the building to halt the advance of the flames. Before they were forced to decide whether or not to blow her up with the Church, there was a Providential wind change and the fire retreated.