The First Parish Meetinghouse of East Derry, NH is preparing for a big anniversary, its tricentennial. What does one even get for a church on its 300th? Wood? Copper? Both, as it turns out. Beginning with a thorough assessment and rehabilitation plan in 2011, the congregation has been working steadily to repair extensive damage throughout the steeple and undercarriage. This past fall, we extracted the belfry and lanterns from the steeple stack. After the new year, we documented the upper sections from a woman-lift and dismantled them from finish to frame.

As we surgically removed trim, we encountered earlier salvage efforts. Dan and Rod peeled back the gracefully curved roof between the upper and lower lanterns and revealed an oiled sailcloth roofing. The sheathing below was labeled November 1916.

The frame was in far worse shape than we expected. Years of roof leaks and patchy repairs had finally overtaken the stout timbers. Once the lower lantern posts were exposed, we wondered how the structure was still standing and realized too late the bravery of dismantling it. Above, you can see that the six of the eight posts were hollow or non-existent at the top. An extensive repair campaign in the 1990s consisted of bolting channel steel and L-brackets to the crossing crab members (a “crab” is a horizontal web of timbers that spans the posts of a lower level and support inboard posts above). Looking at this picture, stiffening the crab fell far from the root of the problem.

The crew struggled to free the timbers from their steel cages only to discover a corpse. It’s tragic that this rot wasn’t addressed when the church raised money for its repair two decades ago. A comprehensive, traditional approach at that time would have prevented the wholesale replacement necessary today.

In 1719, Scotch-Irish immigrants, fleeing religious persecution in Northern Ireland, settled the area that became East Derry. In 1722, they built their first meetinghouse on this site. The present structure was built in 1769. By its centennial, in 1822, the congregation had so grown that they cleaved the building in two and dragged one end 24 feet to the east. Above, you can see the first additional bay, indicated by the absent strainer beam and braces.

In our assessment drawing above, the strainers and bracing between the trussses in bents 3 and 4 and bents 5 and 6 are non-typical. The strainers and bracing in bright green are non-existent; that is the bay in the photograph above. The yellow strainers and bracing between bents 5 and 6 do not quite reach bent 5, they are connected by a series of sisters and scabs. The evidence in the frame complies with the history: our hypothesis is that in 1822 the building was split between bents 3 and 6, (originally bents 3 and 4). Bents 6 through 9 were dragged to their current position, and bents 4 and 5 were built as exact reproductions of the originals. The strainer and braces that used to connect bent 6 (originally 4) to bent 3 were sistered to bent 5, and the strainer between bents 3 and 4 was deemed unnecessary. We are curious to uncover more of the eave wall framing, specifically the plates and the sill scarfs, to see whether there is more evidence to support our theory.

The East Derry First Parish truss is iconic. It has a king post in the center, with parallel rafter-chords and crossing pairs of ascending and descending struts. The king post is in tension, picking up the tie beam at the middle of its span, and the ascending struts rise from the king post and prevent the rafter from sagging. In the Timber Framing series, “Historic American Roof Trusses,” Jan Lewandowski explains:

Outward pressure on the walls can be eliminated entirely by affixing the feet of each rafter couple to their own tie beam. The problem of sag can then be addressed by hanging a joggled vertical member, or kingpost, from these rafters and using it in tension to support the midspan of the tie beam… By a less obvious intuitive leap, it might be realized that the midspan of the long rafters can be kept from bending by struts rising from lower joggles on the suspended kingpost.

The parallel rafter-chord is an innovation that protects the Achille’s heel of the king post truss. The casual observer often assumes that the joint between tie and king post is where we would most frequently see failure over time. I’ve seen many iron stirrups that attest to the builder’s concern for this joint. But most trusses fail at the rafter heel, where the upper rafter-chord intersects the tie beam. Of this foot joint, Lewandowski writes:

Those we can inspect seem more prone to failure and impairment than most other connections in the truss, for a combination of reasons: the lack of relish beyond the mortise and the large forces involved, coupled with the low angle of attack of rafter to tie, all exacerbated by a high incidence of leaky eaves. The significance of the roof slope is that the geometry of low-pitch roofs channels more horizontal force against potential long-grain shear failure in the tie at the foot joint than it does comparable vertical breakout load on the kingpost at the peak (see TF 72, 19). The point: on both empirical and theoretical grounds, the principal rafter-to-tie beam joint is the likely weak sister in the mix.

In Sedgwick, we saw the foot of the upper chord shear a 2″ x 12″ x 22″ block clear off the end of the tie beam (It was about the size of a hefty wedding-present-breadboard). With a parallel rafter-chord truss, the duties of principal rafter and upper chord are separated. The principal rafter, the top angled timber, carries the roof, while the upper chord, the inner angled timber, carries the compressive loads created by the truss. The upper chord intersects the tie beam farther from the end of the beam, thereby protecting the relish just past the joint from shear. We so liked this truss that we reproduced it in a building where it will be on grand display: the Lewis Conservation Center.

Paul Lindemann, East Derry historian and devoted parishioner, keeps a detailed website documenting the history of the church and their repair process. The Nutfield History blog is a fascinating read for anyone interested in New Hampshire history or building history in general. The blog also benefits from Lindemann’s web design skills, something that doesn’t always attend the dual callings of historian and parishioner.

The vigor and ingenuity of the immigrants who built this Meetinghouse is evident in its frame. We honor their labor with our efforts to preserve it. In 300 years, what will historians write about the immigrants seeking refuge in the United States today?