Construction Types and Building Size

 Construction Types and Building Sizes

Construction types are what determine the construction systems and materials that are allowed on both the exterior and interior parts of a building. The construction type also determines the allowable size and height of a building. When it comes to interiors and the need to rearrange building elements, it is crucial to know and familiarize yourself with what changes can be made safely based on the building codes and construction type.

Identifying Construction Types

Each project is different, however, the need to identify the existing construction type remains constant. In addition, researching the fire-resistance rating requirements and building materials allowed by the code are just as critical. Buildings are classified by the lowest-rated element or the use of the most combustible material. Original construction documents are always the best source of information, but occasionally having to consult an architect, building official, or structural engineer on concluding a building’s construction type is just as effective.

Different construction types and their materials.

Based off the IBC, each construction type is defined by the fire-resistance rating that is assigned to each building element. Type I and Type II construction types have the highest level of fire resistant and are almost completely made of noncombustible materials. These types are usually built with steel and concrete; however, the hourly ratings of the structural elements are the biggest difference between the two types. Type III construction type is a mix of both noncombustible and combustible elements but considered to be combustible. The exterior is typically the noncombustible materials, whereas the interior elements and roof are partially – or wholly – constructed with wood.

Construction Type IV is composed of wood structural elements with a minimum cross section and density, so the more strength and fire-resistance is present; this is known as mass timber. Heavy timber, on the other hand, is a structural system composed of solid sawn wood elements that were previously larger sized with more density. With heavy timber, char appears on the surface when it burns, acting as a protectant for the building element. The last construction type, Type V, is the most combustible and an all-wood structure. The framed exterior walls and interior walls are comprised of wood, with a possible veneer on the exterior.

Building Height and Area

Due to the fact that there are limits ti the allowable size and height of a building based off the codes, it is important to understand that the overall size of a building should remain within the allotted height and area limits. These heights and areas are directly related to many factors such as the construction type, occupancy classification and the construction type, use of a sprinkler system, location, fire walls and horizontal separations, and the number of stories, height, and area.

The construction type effects the height and area of a building because, typically, the more combustible materials used and the higher the fire-resistance rating is, the greater allowable building area and height. The occupancy classification, in addition to the building height, set the initial allowable size and height of a building. If more than one occupancy classification is within a building, the allowable size is limited by occupancy classification and allows the smallest area or height. The use of a sprinkler system can permit an increase in height and number of stories and area per floor. It can also result in more allowable area than constructing in a more fire-resistant construction type.

Example of a mezzanine.

The location, as well as the amount of street frontage effects the area of a building
because in the case of fire, additional exterior space prevents flames from spreading or to adjacent buildings. These sorts of codes allow for proportional increase in floor area from what is originally allotted. Fire walls and horizontal separations can be used to divide the total area within a single structure. Each individual building is required to stay in its own size limitation based of the building’s construction type so that an overall continuous structure is can be larger. Lastly, the number of stories, heigh, and area based of the codes definition for what makes a building story or level. The codes also determine whether a mezzanine is part of a story or is its own, separate story.

Conclusion

It is important to always follow up with an architect, structural engineer, or codes official to determine what is allowed within a building before starting any renovations and designing. A code official may also want to analyze any information provided for interior projects. This is because it tells a part of the story and its compatibility of the project type with the existing building.