Tenacre Country Day School


Wellesley, MA

Frederic C. Detwiller

Tenacre Country Day School

Project Description
As the Structural Engineer of Record, Structures North provided the structural design and construction administration for an addition that connected two existing wings of the school. One of the wings of the school originally started as a wood-framed single-family house built in 1927, and the other wing was built in 1947. For this project, the school was looking to add classroom space where presently there was a one-story narrow corridor connecting two wings. The new addition would be two stories, built over the top of the existing corridor, with a walk-able roof that could be used for egress. The architect’s design called for the addition to continue the front walls of the two wings until they intersected at a new corner. With the wide open new 1st and 2nd floor plans, this created a corner condition with no place to install a supporting post. A large bent-steel roof member was designed to carry roof loads over the 2nd floor, avoiding posts in the classroom space. The school wanted certain rooms and hallways adjacent or under the addition to be usable during construction, requiring us to avoid placing new structural supports in existing walls. Instead, a post and beam system adjacent to existing walls was used, with the posts bearing on new concrete piers and footings. The 1st floor slab-on-grade system was raised above previous finish grade, and care was used to prevent adding soil pressure loads to existing foundation walls by using both perimeter grade beams spanning between new piers, as well as a built-up rigid insulation base under the slab. Special precautions were also taken during construction to avoid undermining an existing chimney, the base of which was discovered during excavations to be at a higher elevation than anticipated.