First, permits must be sought for any retaining wall exceeding 36" in the District, and if necessary, a structural engineer may be required to approve the retaining wall construction designs. Retaining walls can be made of many different materials including dirt, rock, concrete, and metal. The type of material used will determine how the wall is built. For example, a wood fence panel can be attached with screws to a steel frame which has been built on site. This would be considered a permanent wall because it's intended to stay where it is placed. A temporary wall can be constructed by placing loose rocks or soil in a line along the property border. These walls are taken down at the end of the building contract. In order to be classified as temporary, the wall needs to be removed at some point during the year. If it's not possible to remove the wall, such as when it's inside the owner's yard, then a structure permit is needed. A permanent wall requires a building permit that covers the construction details including the size, height, and material selection. Examples of permanent walls include brick, stone, and wood. A concrete block wall that is painted white or gray does not require a permit since it is considered a surface treatment and not a structural element.