Built in 1735, the Old Treasury Building is one of the oldest public buildings still standing in Maryland. The one-story building measures about 42 x 45 feet and is laid out in a cruciform plan. It is on the grounds of the Maryland State House, occupying a part of State Circle near the Capitol building.

The exterior walls are brick-laid in Flemish bond, varying in color from orange to red to brown to dark purple. At one time, the brick masonry had been tuck-pointed with a hard cement mortar, and in certain areas re-laid in portland cement. WEI removed the existing modern mortars and re-pointed the building with an appropriate lime-based mortar. Any bricks that had become loose or lost their bond with the mortar were reset.

Non-masonry work included installing an ADA-compliant door in an existing window space and installing a drainage system around the perimeter of the building.