The Height of Buildings Act of 1910 was an Act of Congress passed by the 61st United States Congress on June 1, 1910 to limit the height of buildings in Washington, D.C.  The original act was passed on March 1, 1899 when the 55th United States Congress approved the Height of Buildings Act of 1899 .  The original act restricted the heights of any type of building in the United States capital city of Washington, D.C., to be no higher than 110 feet (34 m). In 1910, the 61st United States Congress enacted a new height restriction law limiting building heights to 130 feet (40 m), or the width of the right-of-way of the street or avenue on which a building fronts, whichever is shorter. That is the main law presented by this act.
In response to the construction of the 164-foot (50-meter) Cairo Hotel in 1894, D.C. Commissioners issued height regulations for buildings in D.C., limiting their height to 90 feet (27 m) for residential and 110 feet (34 m) for business, or to the width of the street in front, whatever was smaller.  The original Height of Buildings Act, passed by Congress in 1899, removed the front street restriction, but reaffirmed limiting buildings to 90 feet (27 m) on residential streets and 110 feet (34 m) on business streets. It also made an exception for buildings on business streets 160 feet (49 m) wide, which were permitted to be 130 feet (40 m) tall.  The 1899 act was amended in 1910 to add the restriction that the height of any building would be limited to the width of the adjacent street plus 20 feet (6.1 m) up to a maximum of 90 feet (27 m) on residential streets, 130 feet (40 m) on commercial streets, and 160 feet (49 m) on a small portion of Pennsylvania Avenue; thus, a building facing a 90-foot (27 m)-wide commercial street could be 110 feet (34 m) tall.
The amendment contains nine sections, though Section 5 enforces the restriction of heights of buildings in the city. Section 5 of the Building Height Amendment Act of 1910, 36 Stat. 452 (formerly codified as amended at D.C. Code Ann. § 5-405 (1994)) ("Height Act"), contains limitations on the permissible heights of buildings in the District of Columbia. Those limitations depend on the width of the street on which a building will front, and on whether the street is a business or a residential street. In addition, the Height Act provides that the maximum height of buildings on blocks adjacent to public buildings "shall be regulated by a schedule adopted by the Council of the District of Columbia." Since 1910, the Commissioners of the District of Columbia, and subsequently the Council, have exercised their authority to set such further height limitations under a Schedule of Heights in 15 different areas of the District adjacent to public buildings, including the blocks around the White House , the Supreme Court building , and the congressional office buildings . 
Section 5 of the Height Act, as amended, provides in pertinent part:
- (a) No building shall be erected, altered, or raised in the District of Columbia in any manner so as to exceed in height above the sidewalk the width of the street, avenue, or highway in its front, increased by 20 feet (6.1 m); but where a building or proposed building confronts a public space or reservation formed at the intersection of 2 or more streets, avenues, or highways, the course of which is not interrupted by said public space or reservation, the limit of height of the building shall be determined from the width of the widest street, avenue, or highway.
- (b) No buildings shall be erected, altered, or raised in any manner as to exceed the height of 130 feet (40 m) on a business street or avenue . . . except on the north side of Pennsylvania Avenue between 1st and 15th Streets Northwest, where an extreme height of 160 feet (49 m) will be permitted.
- (c) On a residence street, avenue, or highway no building shall be erected, altered, or raised in any manner so as to be over 90 feet (27 m) in height at the highest part of the roof or parapet . . .
- (d) The height of a building on a corner lot will be determined by the width of the wider street.
- . . . .
- (f) On blocks immediately adjacent to public buildings or to the side of any public building for which plans have been prepared and money appropriated at the time of the application for the permit to construct said building, the maximum height shall be regulated by a schedule adopted by the Council of the District of Columbia.
- (g) Buildings erected after June 1, 1910, to front or abut on the plaza in front of the new Union Station provided for by Act of Congress approved February 28, 1903, shall be fireproof and shall not be of a greater height than 80 feet (24 m).
- (h) Spires , towers , domes , minarets , pinnacles , penthouses over elevator shafts, ventilation shafts , chimneys , smokestacks , and fire sprinkler tanks may be erected to a greater height than any limit prescribed in this subchapter when and as the same may be approved by the Mayor of the District of Columbia; provided, however, that such structures when above such limit of height shall be fireproof, and no floor or compartment thereof shall be constructed or used for human occupancy above the top story of the building upon which such structures are placed; and provided, that penthouses, ventilation shafts, and tanks shall be set back from the exterior walls distances equal to their respective heights above the adjacent roof; and provided further, that a building be permitted to be erected to a height not to exceed 130 feet (40 m) on lots 15, 804, and 805, square 322, located on the southeast corner of 12th and E Streets Northwest, said building to conform in height and to be used as an addition to the hotel building located to the east thereof on lot 18, square 322; and further provided, that the building to be erected on lots 813, 814, and 820, in square 254, located on the southeast corner of 14th and F Streets Northwest, be permitted to be erected to a height not to exceed 140 feet (43 m) above the F Street curb; and provided further, that the building to be erected on property known as the Dean Tract, comprising nine and one-fourth acres, bounded on the west by Connecticut Avenue and Columbia Road, on the south by Florida Avenue, and the east by 19th Street, and on the north by a property line running east and west 564 feet (172 m) in length, said building to cover an area not exceeding 14,000 square feet (1,300 m 2 ) and to be located on said property not less than 40 feet (12 m) distant from the north property line, not less than 320 feet (98 m) distant from the Connecticut Avenue property line, not less than 160 feet (49 m) distant from the 19th Street property line, and not less than 360 feet (110 m) distant from the Florida Avenue line, measured at the point on the Florida Avenue boundary where the center line of 20th Street meets said boundary, be permitted to be erected to a height not to exceed 180 feet (55 m) above the level of the existing grade at the center of the location above described; and provided further, that the design of said building and the layout of said ground be subject to approval by the Fine Arts Commission and the National Capital Planning Commission , both of the District of Columbia; and further provided, that the building to be erected by the Georgetown University for a hospital as a part of the Georgetown University Medical School on parcels 28/31, 28/36 and 28/37 located on the south side of Reservoir Road Northwest in the District of Columbia, approximately opposite 39th Street, plans for which building are on file in the Office of the Inspector of Buildings of the District of Columbia, be permitted to be erected to a height of not to exceed 110 feet (34 m) above the finished grade of the land, as shown on said plans, at the middle of the front of the building.— D.C. Code Ann § 6-601.05
For the other eight sections, see [DC ST § 6-601].
Tallest buildings in Washington, D.C.
The Basilica of the National Shrine of the Immaculate Conception , completed in 1959, was granted an exemption to the law by the District Zoning Commission.  The National Shrine stands as the tallest building in Washington, D.C. , excluding the Washington Monument (555 feet (169 m)) and the Hughes Memorial Tower (761 feet (232 m)). When the original act was passed in 1899, the Old Post Office Building was grandfathered in, and remains as the tallest high-rise federal building in the city.  The tallest commercial building in Washington, D.C. (another one granted an exception) is One Franklin Square , the fifth highest building in the city, which was completed in 1989 and rises to 210 feet (64 m). 
Proposed policy changes
The current policy of the 1910 Height Act has been in place with only small modifications for over 100 years. Its influence on the development of the city both within the monumental core and beyond has shaped Washington's skyline. In order to determine if the city could be provided some relief related to building heights within the original boundaries of the L’Enfant Plan and a loosening of federal oversight outside of the monumental core while protecting federal interests, a revisiting of policy was deemed warranted by Congress at this time.
One specific issue the District of Columbia government identified that is impacting development within the downtown core is the law prohibiting the use of the penthouse level (i.e. roof) for needs other than mechanical (i.e. HVAC equipment) structures. For example, the height of a building as calculated by the Height Act does not include roof top structures used for mechanical needs within the total allowable height. However, if structures on the roof top (such as a pool house associated with a roof top pool) are constructed for human occupation, it is then calculated as part of the overall height of the building under the law. As a result, architects and designers currently would have to lower their building designs by an entire floor to allow for some human occupied space on the roof, if the building is to reach the maximum allowable height. By allowing usable, human occupying space at the penthouse level, the District of Columbia is arguing that there would be no real impact on the overall height limit and it would not change the “human scale” of the current landscape within the city. The current allowable height within the downtown area of the city prohibits “people’s enjoyment of some of the city’s greatest spaces and most striking views”.
The second problem identified focuses on the area of the District of Columbia outside of the original Federal City laid out by L’Enfant. This area is typically north of Florida Avenue, NW (originally known as Boundary Avenue) and east of the Anacostia River. The passage of the 1973 District of Columbia Self-Government and Governmental Reorganization Act (Home Rule Act) allowed for many local government functions to be controlled at the local level for the first time. However, within the Home Rule Act, Congress specifically stated that the DC Council does not have the authority to “enact any act, resolution or rule which permits the building of any structure within the District of Columbia in excess of the height limitations contained in Section 5 of the Height Act.”  The District of Columbia can argue that its local zoning regulations are as stringent, if not more stringent, in managing building heights throughout the District.  The local government has been a strong steward of the evolving architectural landscape of the city through zoning and preservation laws since gaining control through the Home Rule Act. 
On November 19, 2013, the National Capital Planning Commission released their final recommendations regarding the Height Master Plan for Washington, DC. The plan, which looked at the question of possible changes to the Height of Buildings Act of 1910, also reviewed "who or what entity should manage building heights....[and] gave voice to questions related to Home Rule as well as the role of the U.S. Congress...".  The Commission has put forth four recommendations for Congress' consideration that would include both keeping the status quo in one instance, but proposing policy changes in the other. The first recommendation focuses on the area of the District of Columbia within the original L'Enfant city. "Due to the concentration of federal interests within the L'Enfant City and to protect the integrity of the form and character of the nation's capital, the federal Height Act should remain in place and no changes should be made to the formula or approach for calculating allowable building height."  The second recommendation focuses on the area outside of the L'Enfant City and provides the District of Columbia government a mechanism in which to identify targeted areas in the city where they could proposed building heights to exceed the maximum currently allowed by the 1910 Height Act. "These may be authorized through the existing Comprehensive Plan process, pending Congressional approval. Should such targeted exceptions be authorized through the Comprehensive Plan , the Height Act would remain in place for all other areas both inside and outside of the L'Enfant City."  The third recommendation focuses on the important vistas that currently exist within the city. "The city's most significant viewsheds, to include without limitations, those to and from the U.S. Capitol and White House, should be further evaluated and federal and local protections established, which include policies in the Federal and District Elements of the Comprehensive Plan ."  Finally, the last recommendation is in response to a specific request that the District of Columbia government put forth before Congress during the hearing in 2012. The National Capital Planning Commission agrees and recommends amending "the Height Act to allow for human occupancy in existing and future penthouses, with restrictions."