When John and Martha Thornberry built their home at Sudley, they also built an outdoor kitchen. The Thornberrys located the kitchen to the east of their dwelling and build a structure measuring 15 by 15 feet with a hearth on the eastern wall. Beneath the kitchen, the Thornberrys dug a root cellar to store their vegetable and fruits through the winter. The root cellar was placed under the kitchen to protect it from burrowing animals and also to ensure that frost would not reach the stored food. Access to the root cellar was likely facilitated by removal of a few floor boards in the kitchen.

The root cellar of Sudley Post Office consists of a square hole dug through bedrock to a depth of five feet through bedrock. Once excavated, the soil was thrown back into the hole and served as a "soft spot" that could be dug into to place vegetables. The depth of the root cellar allowed food to be stored below the frost line and close to the water table. This environment has the effect of keeping the vegetables and fruits in a cool moist environment similar to a refrigerator. Vegetables were placed in the root cellar by digging a hole, known as a "vegetable kiln" into the fill, lining the bottom with hay, arranging the fruit and vegetables in the hay, and then placing soil back on top. Archaeological excavation of the root cellar at Sudley Post Office revealed three of these vegetable kilns. These kilns were softer patches of soil within the root cellar fill that were round in shape (see photo at right). When it was time to eat the vegetables, the vegetables were simply dug up. Local residents in the Manassas area recall that apples placed in such vegetable kilns would stay as fresh as the day they were placed in the hole.

Archeological excavation of the root cellar at Sudley Post Office not only revealed the presence of the vegetable kilns within the root cellar fill, but the history of its use through time. Artifacts were recovered throughout the fill of the root cellar. Manufacturing dates of these artifacts revealed that the Thornberry and Davis household used this root cellar. Once the Davis family left Sudley Post Office in the late 1920s, the kitchen fell into disrepair and eventually collapsed into the root cellar. The collapse of the kitchen into the root cellar was revealed by a thick layer of chimney rubble overlying the metal roof of the kitchen (see photos below ). The placement of the chimney rubble on top of the roof hints that with the decay of the structure, the chimney collapsed onto the roof and into the root cellar. Later occupants of the site filled in the slump of the kitchen/root cellar with soils and debris from around the site. The outline of the kitchen/root cellar could be seen as a slight depression when archaeologists first visited the site.

Photograph of rubble fall from the collapsed kitchen chimney. These rocks were mixed with and overlay fragments of metal roofing from the kitchen. Notice the springs from a carriage seat in the center of the photograph (circled in red).

After the rock rubble was removed, the top layers of the root cellar (shown above) were revealed. The white arrow rests on bedrock into which the root cellar was excavated. The bedrock below the arrow forms the eastern wall of the root cellar.