The purpose of this page is to help the reader to understand how the Architect selects the type of construction for the building and the spaces within the building. Most of the time, this factor is determined based on the construction costs and long term use costs of the material chosen.
If viewed on a sliding scale, as the building code requirements are increased, construction materials that are less appropriate start to ‘drop off’ and the ones that are relevant remain. As an example, for interior construction, if there are 2 different uses, say, a hazardous use that is adjacent to a residential use, there is a high required rating of the wall construction – the wall should maintain a 3 hour construction rating (according to building code Table 508.4). If there are two of the same uses such as a business use next to a business use, the code doesn’t require a specific hour separation rating. Since each situation is different, the architect needs to evaluate the rooms on a case-by-case basis.
The hour rating of a given wall or assembly of materials in a floor / wall / ceiling combination requires less combustible materials as the number of hours rating increases. So, materials such as wood can be used for lower hour ratings and steel / concrete / concrete block are to be used for higher hour ratings requirements.
Therefore, if one knows the required hour rating and separation, then one may also be able to determine / decide on the category of wall construction. I said ‘decide’ because at times there may be options if the same rating type can be accomplished by two different construction classifications. In our example above, where we have 2 rooms that are adjacent sharing the ‘B’ classification, any Fire-Resistance Rating that has a zero-requirement of hour separation would be sufficient.
The wall in question must first be assessed to determine if it is carrying more than its own weight in order to stand up. If it is the case that it is bearing more weight than that, the wall is a bearing wall. Most exterior walls are bearing walls. Some interior walls are bearing walls. The determination of whether the wall is bearing or not combined with its location is the driving factor in the selection of the wall’s construction classification. An interior non-load bearing wall has no specific hour rating classification, so the wall can be classified with any Fire Resistance Rating. Check Table 601 for more information.
(Note: If you have found the information here helpful and would like to purchase a copy of the building code for yourself through one of our affiliate links, where no charge is added to your bill, but we receive a small commission from Amazon, you can click on this link: 2013 California Building Code, Title 24 Part 2 (2 volumes – includes parts 8 & 10)