The Union Iron Works Machine Shop Building (Building 113/114), built in 1883 (some sources say 1886), is the oldest surviving building in the Pier 70 area, and the most historically significant. One of the first structures built when Union Iron Works moved here, it was designed to make use of the most advanced and efficient industrial practices in the world at the time. (See Pier 70 Brief History.)

It was in the machine shop that the iron and steel equipment needed for large ships was fabricated. Everything from small parts to complete engines was within the capability of the skilled workers who were employed here.

Building 113 has been in active use as a machine shop up until the present, used for ship repair tasks in recent years rather than those needed for shipbuilding.

It is an unreinforced masonry building. In early 2004, machine shop and all other work functions ceased in the building after continuous use for almost 120 years due to seismic safety issues. The Port of San Francisco is planning to “mothball” Building 113/114, along with Building 104 across the street. This means that it will be boarded up and fenced until suitable plans can be developed for reinforcement and re-use.

Its 450 foot long structure of the machine shop, Building 113, consists of two original brick structures, dating from 1886, connected by a circa 1914 reinforced concrete infill structure. Both brick structures have gable roofs, projecting piers, arched windows and simple corbeled cornices. Largely undecorated, the building is characterized as a long horizontal mass with a steep gabled roof.

The smaller Building 114, connected to and immediately south of Building 113, was orignally used for forges. It is of similar design and the two structures are usually referred to together.