Sealing a building so water will not enter is called dry floodproofing. The interior spaces, equipment and contents of the building stay dry. Dry Floodproofing is the type of floodproofing that is certified using FEMA's Floodproofing Certificate. It is the only type that can be used as an option to elevation for making a non-residential building compliant with flood damage prevention ordinances.

Permanent dry floodproofing of an existing building can be done by applying a long-lasting, waterproof sealant coating or membrane over the exterior sheathing, siding (if relatively flat) or brick veneer. During a flood penetrations in the walls must be sealed watertight, including central air-conditioning condensate drains, openings for telephone and electrical lines and any other channels through the walls. In addition, all doors and windows need watertight panels that can be closed to block flood water. (See Panel Closures) Some of the openings may be sealed permanently. Temporary dry floodproofing by wrapping with plastic is described under Temporary Barriers More on Dry Floodproofing. Also visit the Back-flow and Panels rooms of the Mall.