This installment of Navigating the Building Code examines construction type and why it is important. Construction Type is a classification of a building or structure that determines fire-resistance rating requirements. Construction Type has a direct impact on the allowable area of the building, the number stories of the building, and the building height above the grade plane. The purpose of classifying buildings and structures in this way is to protect the structural elements from fire and collapse, and to divide the building into compartments so that a fire in one area can be contained long enough to allow people to remain safe until firefighters can arrive. Within the code are charts and tables that show the requirements for the different fire-resistance ratings for building elements for each Construction Type (Chapters 5 and 6 in the International Building Code).
Construction type is based on the materials and fire-resistance properties of the main building elements. The components in question, but not limited to, are the structural frames, bearing walls, exterior and interior non-bearing walls, floors, and roof construction. There are five classifications types for construction, and are aptly labeled as Type I, II, III, IV, and V. Type I are the most fire resistive, while Type V is the least fire resistive. Types I and II are constructed from noncombustible materials, while types III, IV, and V are considered combustible. Also, each type is further sub-divided into “A” or “B” types, where the construction assemblies that separate spaces need to be considered. Generally, rated separation is need for “A” types and is more fire resistive than “B” types, where fire rated separation is not needed. Therefore, generally speaking, Type IA is the most fire-resistive and Type VB is the least.
Let’s look at a quick look at each Type:
Type I are those types in which building elements and components are of noncombustible materials. The assemblies are constructed in such a way that they are the most fire restrictive in terms of rated-hours (generally it is at least 2 hour rated or greater construction, however, each scenario is explained in the code and needs to be followed accordingly).
Just as in Type I, Type II are those types in which building elements and components are of noncombustible materials. However, the assemblies are constructed in such a way that they are the less fire restrictive in terms of rated-hours (generally it less than 2 hour rated, however, each scenario is explained in the code and needs to be followed accordingly).
Type III are those types in which the exterior walls are of noncombustible materials (and 2 hour rated assemblies) and the interior building elements can be of any material.
Type IV are those types in which Heavy Timber construction is used. This construction type is highly specific and special care needs to be taken in terms of referencing the code allowances.
Type V are those types in which the structural elements, exterior walls, and interior walls can be constructed by any materials (noncombustible or combustible) permitted by the code.
Allowable Area, Number of Stories, and Building Height
Construction Type is the classification that determines the maximum allowable area of the building, the number stories the building is permitted to be above the grade plane, and the overall building height. A building that is the most fire-resistive (Type IA) has the least amount of size restrictions. Generally speaking, although not in all cases, Type IA buildings are unlimited in their size. A building that is the least fire-resistive (Type VB) has the most amount of size restrictions. As you can see, Construction Type, therefore determines a building’s overall form and massing. The form and massing has a direct impact on the operations in a floor plan and functions and aesthetics of the exterior. By having an understanding of how Construction Type is determined and applied to your project you can best decide what is and what is not possible for your project.
Also, to reiterate a few important points from previous posts, keep in mind that there are other regulations and rules set forth by the authorities having jurisdiction over your project. You and the architect must identify what is in place for the project to ensure that the project is designed correctly. In order to maintain the health, safety, and welfare of the general public, the architect and client needs a thorough understanding of the building codes and be able to adapt the design practices to meet the needs of the code. You are more than welcome to contact us regarding any questions you may have regarding building codes and the effect of regulations on your project – firstname.lastname@example.org