CHALLENGE
Built between 1893 and 1894, Essex Town Hall is listed on the National Register of Historic Places. The building has a stone masonry exterior wall at the ground floor with 1½ stories of wood framed construction above and contains a administrative offices, a public library, and an auditorium. The building was exhibiting signs of water infiltration in the basement, leading to wall cracks and structural shifting in some walls.
The occupants of the Town Hall building also noticed cracks formed in the plaster and stone masonry adjacent to the east wall of the building. There were also significant gaps at the baseboard of a stair landing adjacent to the wall and the stone masonry appeared to be bulging outward.
CBI’S SOLUTION
After investigating, the water infiltration problem into the basement area turned out to be an unusual situation. The thinking has always been that the water table is high and sloped down from the hill causing the basement to be wet. The Town Hall building was actually sitting in a clay “bathtub” which was not allowing significant water to percolate through. The water problem appears to be the result of water penetrating the wall and collecting on top of the impermeable clay below the floor slab with no place to drain to. The building was in need of a drainage system to divert ground water from infiltrating the basement.
After brainstorming a few different ideas, we recommended an interior drain below the floor slab and around the entire perimeter of the basement as accessible. We also recommended applying a cementitious parge coat of mortar over repointed stone joints along with the interior face of the stone masonry to direct water to the drain. This system would collect any water reaching the clay and direct it out of the building. A new concrete slab over a vapor barrier completed the interior waterproofing. We also recommended collecting the water coming off the roof into gutters and downspouts, using new below ground piping directed away from the building.
For cracks on the east wall, CBI reviewed the conditions and recommended temporary bracing be installed on the exterior side of the stone masonry to inhibit further movement outward. CBI provided a sketch and the bracing was installed quickly. CBI then analyzed the framing and masonry to determine the possible cause of the movement at the east wall. We determined that the detailing of the original timber sill above the masonry wall, in conjunction with a lack of bracing, led to the outward movement of the wall.
CBI also reviewed existing water-damaged wood stud framing in the stairwell. There was significant rot in some of the studs and in portions of the landing framing. To counter this, a new stud bearing wall was installed to replace the old and mitigate further related structural damage in that area. Still, it was important to find the source of the water infiltration to prevent further damage in the future. The Town had plans for subsequent building envelope renovation, so in the interim, CBI recommended removing the damaged material down to sound wood and treating the remaining wood directly adjacent to the damage with a preservative agent.
