Codman Estate woodshed structural work
May 6, 2010
Damaged clapboard siding on the left side of the front elevation indicated possible structural damage to the corner post of the main structure. Careful removal of the damaged clapboards revealed extensive rot in both the sheathing and the building frame. The rot affects the sill of this wall section, the corner post to a height of twelve feet, and the bottoms of all the wall studs (at the sill). Additionally, the rot has damaged four horizontal members where they are joined to the corner post. The front and end-bearing beams/girts supporting the second floor are joined with mortise and tenon to the corner post and both tenons are damaged.
The top plate of the one-story shed structure is only toe-nailed to the corner post and is substantially damaged. The diagonal header/brace for the sliding door frame is also toe-nailed into the corner post and is similarly damaged by rot.
Water appears to have entered the wall assembly at the intersection of the lower roof and the wall. The joint is not well detailed and lacks kick-out flashing that would direct water away from the wall below. On the interior, the wall assembly is covered with gypsum board and filled with fiberglass batt insulation. This combination likely served to prevent drying to the interior. The fiberglass especially would have held moisture in the wall cavity, accelerating the deterioration of the framing members.
The area exposed by this repair illustrates an interesting hybrid of heavy timber construction and platform framing. The large dimension post and girts/beams of the central two-story portion of the building are joined with mortise and tenon construction, while the elements of the smaller one-story wing are simply butted and toe nailed to the larger structure
The framing will be replaced in kind, using like methods to complete the repairs. The only proposed deviation is the use of a more naturally rot-resistant wood for the sill – perhaps white oak or black locust – a decision yet to be made. Sheathing, clapboards, and trim boards should be replaced in kind, primed on all six sides.