We all know that openings in a wall are important, who would want to live in a closed box not being able to get out? Properly designing and constructing openings is crucial to the safety of a structure. Openings can include any cut out of a wall segment, for example, windows and doors. Cutting into a load bearing wall impacts the design of not just the wall the entire system itself. Each part of a puzzle affects the entire puzzle as a whole, which is the same idea as a structure. For this topic, the importance of designing window openings will be looked at.
When a design calls for a window, the wall surrounding it has to be built properly. This means that the loads being applied to the wall have to be now sure the loads being applied can still be transferred down the building as if no window was added. To understand what an opening does to a wall, the picture below shows a typical wall framing system.
The typical wall framing system above shows what wall framing looks like with an opening. Surrounding the opening are the parts that are being focused on, these are the header, jack (trimmer) studs, and king studs. A header is designed to carry the load of the size of the opening. It is because the stud spacing was interrupted and the load needs to be transferred from one side of the opening to the other. The jack or trimmer studs are the studs that the header bears on meaning it supports the header. These studs transfer the load from the header down the bottom plate and onto the next framing element. The king stud is the full-length stud attached to the trimmer stud, supporting the header and trimmer stud. Based on the loads being applied and the design requirements for the opening will determine the size and building material needed for the header. Based on the header design will determine the quantity and size of the trimmer and king studs needed. The International Residential Building code supplies a table shown below that shows the required amount of trimmer and king studs based on the size of the window and spacing of the studs. Keep in mind that this table gives the required number of trimmer studs for the basic size of windows, this table does not include any unique loads that would require more support than give. For these cases, please use engineering judgment and caution on the necessary number of studs required to successfully support the window opening.
Without the necessary trimmer and king studs, the header will not be properly supported, the load will not transfer down to the next framing element, crushing of wood members, and overall not a very happy window to look out of.
