When we began the restoration of a historic stone granary in Northern Virginia, we knew that creating a dry basement was crucial to the success of the project. The four-story building dated from the early nineteenth century and its owners planned to use it as living space. When we began our work, the cellar was a mess, its dirt floor full of mud, with seasonal streams of water running across it. Most of the framing on this level was badly deteriorated and would have to be removed, including the first-story floor joists. The plans called for the basement to be conditioned and for the mechanical equipment to be located there, so we knew we had to deal with the moisture.

Our first approach to the problem was to build retaining walls on each side of the cellar door. We excavated downslope to facilitate runoff, and added fill upslope in several places to provide positive surface drainage around and away from the building. Even after these improvements were completed, there was still a lot of water moving through...

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