Occupied Roof Decks and Allowable Building Size

由于建筑设计师和业主试图通过提供屋顶平台等设施来增加市场吸引力，在多户住宅和皇冠2登录welcome建筑中，屋顶被占用变得越来越普遍. In most cases, 这些屋顶平台是开放的，周围有半高的墙/护墙. However, 部分或全部屋顶甲板空间也可以用全高的墙壁和屋顶覆盖物封闭起来. In both scenarios, 经常出现的问题包括屋顶甲板是否需要被视为一个单独的楼层，以及在评估基于特定建筑类型的高度和面积要求时，占用率和面积如何起作用.

Code language regarding this topic continues to evolve. Under the 2012 and 2015 IBC, some feel that the relevant code provisions leave room for interpretation. As such, 设计团队可以选择与拥有管辖权的当局(AHJ)就他或她认为可接受的内容进行磋商. 即将纳入2018年IBC的代码变更进一步澄清了有关该主题的规定(见下文).

In the meantime, following is a summary of how designers in the U.S. 是否在其项目中成功地实施了占用屋顶平台，而没有将其包括在建筑物的总高度内, number of stories and area.

Roof Decks without Roof Coverings

IBC 2012 Table 503 and IBC 2015 Table 504.4 provide limitations on allowable number of stories in a given building. However, per the definition of a story in IBC Chapter 2, 从技术上讲，没有上面结构的屋顶空间不符合其定义:

STORY. 地下室:建筑物的一部分，包括在一层的上表面和下一层的地板或屋顶的上表面之间(也见“地下室”,” “Building height,” “Grade plane” and “Mezzanine”). 它是用连续两层梁或成品地板表面从顶部到顶部的垂直距离来测量的, for the topmost story, from the top of the floor finish to the top of the ceiling joists or, where there is not a ceiling, to the top of the roof rafters. 

Additionally, for most common roof deck spaces, none of the roof area would classify as a habitable space as defined in IBC Chapter 2:

HABITABLE SPACE. A space in a building for living, sleeping, eating or cooking. Bathrooms, toilet rooms, closets, halls, storage or utility spaces and similar areas are not considered habitable spaces.

IBC 2015 Section 1006.3 .增加了明确承认存在被占用的屋顶并规定与之有关的出口要求的文字;

1006.3 Egress from stories or occupied roofs. 适用于任何楼层或有人使用的屋顶的出口系统，须根据根据本条提供服务的总载客量，设置出口数目或出口通道. The path of egress travel to an exit shall not pass through more than one adjacent story.

将于2018年生效的已批准的代码变更支持这一点(见代码变更G24-15), public comment #2). IBC 2018 Section 302.1, which covers occupancy group definitions, includes the following to clarify how occupied roofs are classified: “Occupied roofs shall be classified in the group that the occupancy most nearly resembles, according to the fire safety and relative hazard involved and shall comply with Section 503.1.4.” Section 503.1.4提供了不要求将占用的屋顶包括在建筑物的层数或面积内的选项.

503.1.4 Occupied roofs  屋顶水平面或其部分须准许用作有人使用的屋顶，但该屋顶的占用情况须符合表504所准许的占用情况.4 for the story immediately below the roof. 根据第506条的规管，占用屋顶的面积不得包括在建筑面积内. 

Exceptions:

1. 位于已占用屋顶上的可占用空间，不应限于紧挨着屋顶的楼层允许的可占用空间，该楼层按照第903节的规定配备了自动喷水灭火系统.3.1.1 or 903.3.1.2 and occupant notification in accordance with Section 907.5 is provided in the area of the occupied roof. 
2. 第I类或第II类建筑的露天停车库的屋顶允许进行集会, in accordance with the exception to Section 903.2.1.6.

包围被占用的屋顶区域的构件或结构的延伸不得超过被占用的屋顶表面48英寸. 

Exception: Penthouses constructed in accordance with Section 1510.2 towers, domes, spires, and cupolas constructed in accordance with Section 1510.5 

Although these changes won’t go into effect until the 2018 IBC, 一些设计师已经使用这种被认可的语言来证明占用屋顶和相关的建筑尺寸分析的合理性. 在波特兰市的以下上诉裁决中可以找到批准占用屋顶甲板的例子, OR.

Appeal 13911

Appeal 9698 (see Appeal Item 5)

Appeal 10399

Appeal 10400 (see Appeal Item 1)

When evaluating the impact of occupied roof decks on the overall building size limitations, another consideration is whether the project qualifies as a high-rise building. IBC第202条将高层建筑定义为“建筑物的使用楼层高于消防车辆通道的最低高度75英尺(22 860毫米)以上。.“IBC第403条规定了适用于高层建筑的具体规定. If the occupied roof deck exceeds this 75-foot limitation, 建议与有管辖权的当局讨论这个问题，以确定是否需要适用高层规定. Through use of IBC Section 104.11, Alternate Design and Methods of Construction, 一些超过这一限制的项目已经成功获得批准，不需要被归类为高层建筑. In many of these cases, 接受的基础是，占用的屋顶平台面积相对较小和/或直接满足下层的需要，并被视为该层的延伸.

Roof Decks with Roof Coverings

In general, 已占用的屋顶空间(上面有结构)用于集合占用(a -2)，根据楼层的定义(见上文)，将被视为一个楼层。. 当甲板高度不超过2-3层时，根据建筑类型和是否使用洒水装置，将屋顶甲板视为一层是可以接受的. When exceeding this height, the most feasible alternative is to consider it an accessory occupancy (IBC 2012 505.2 and 508.2). The accessory provisions may potentially be applied to common spaces, provided they are no larger than 10% of the floor area they serve. Alternatively, the small assembly space provisions of IBC Section 303.1.2 could be used to classify the occupied roof space as Group B, provided the limitations of that section are met. 使用这部分的优点是B组占用通常比A-2组占用允许更多的楼层.