DPWES Letters to Industry
Land Development Services
12055 Government Center Parkway
703-324-1780, TTY 711
July 1, 2006
Certification of Building Heights for Single Family Detached and Townhouse Units
Issue: Building height calculations have been improperly calculated and/or not been adequately depicted on residential plan submissions.
Background: Plan reviewers are finding that the building height on grading and building plans for single family detached units and on construction plans for townhouses are either omitted or improperly calculated. The bulk regulations pertaining to building height and minimum yard regulations are an integral part of grading plans and site plans and must be accurately shown to ensure code compliance. Information provided on the building permit normally states the maximum permitted height and not the actual building height. Additionally, architectural plans do not show building height as it relates to actual finished grades. Set forth below is the methodology for calculating building height in accordance with the Zoning Ordinance building height definition. This methodology is based on a long-standing Zoning Ordinance interpretation for measuring building height and is not a change in practice. Also set forth below are revised procedures for depicting and certifying height on plan submissions.
Procedures: Effective immediately, all bonded grading plans and infill grading plans for single family detached dwellings and all site plans for townhouses shall provide and certify the actual building height by providing the elevation of the average grade around the perimeter of the dwelling unit (“average grade”) as set forth below and the roof height calculated as set forth below.
All architectural plans for single family detached and townhouse projects shall certify the height of the structure from the front stoop to the mid-point of the highest roof so that this information can be cross-referenced with the average grade and overall height certification set forth on the grading plans and site plans.
Additions to homes that do not require a grading plan will also require the applicant to certify to the building height on the architectural drawings and may require a certified survey of the structure height.
The house model and elevation type shall also be provided on the grading plans so that they may be cross-referenced with the building permit. Grading plans that are using an approved master file house plan must provide the ridge and corresponding eaves elevations of the highest roof from the approved master file. Custom homes shall be labeled as “custom” and will not be required to show the model and elevation type. A certified height survey may be required to validate the building height prior to the issuance of the residential use permit.
Clarification of Building Height Methodology – In accordance with the long-standing Zoning Ordinance interpretation, the building height for both detached and townhouse units, is measured from the average grade to the following roof points:
- for flat roofs – to the highest point
- for mansard roofs – to the deck line;
- for gable, hip or gambrel roofs – to the average height (mid-point) between the ridge and the corresponding eaves of the highest roof line. If the eaves are uneven, the mid-point between the ridge of the highest roof line and each eave, then the average of these midpoints.
For single family detached units, the average grade shall be calculated by taking elevation points around the perimeter of the structure at intervals of approximately 20 feet, and averaging them. For townhouse units, average grade shall be calculated for each individual unit, rather than around the perimeter of the entire building group/row. For interior units, a minimum of two elevation points shall be taken at both the front and rear exteriors of the unit and averaged. For end units, a minimum of two elevation points shall be taken on the front, side and rear exteriors of the unit and averaged.
All such elevation points shall be shown along the perimeter of the structure and in tabular form on the grading plan. The actual building height of the dwelling unit shall be presented by subtracting the average grade from the roof height. It is noted that the lower elevations of window wells, no more than 10 feet wide along the wall of the building, and extending from the structure no more than 4 feet, and areaways or walk-outs with widths along the wall of the building that do not exceed a maximum of 15 feet, are not included in the average grade calculation. Finished grades that are established with a retaining wall must extend 10 feet from the structure, in order to include the higher grade elevation toward the average grade calculation. Grades established by a retaining wall that extend less than 10 feet from the structure, are measured at the base of the retaining wall.
If you have any questions or need additional information, please contact the Environmental and Site Review Division at 703-324-1720, TTY 711.