We’ve recently received a large number of inquiries for braced wall designs for residential homes in the New England area. This type of structural design, although not new, has been generating much more steam and being enforced more often. What is it and how does it affect what you may be building?
The purpose of braced wall design
Braced walls are often used in wood construction applications. Their purpose is to resist the lateral (or horizontal) forces applied to the building, typically applied by wind and seismic (earthquake) events. This is very different than gravity loads, such as snow, rain, people (i.e. live loads), or dead loads, which typically act up and down vs. side to side.
Is this a new structural engineering concept?
Braced walls are not new, and in most cases, contractors already install them without knowing.
The prescriptive requirements in the International Residential Code (IRC) for this design are still relatively young, very lengthy, and not an easy read. Building officials are becoming more educated about how they work and what is often necessary in their design. More and more often the building officials require that the design be incorporated into the building plans.
How to construct a braced wall
There are several methods outlined in the IRC of how to construct a braced wall. The three most common methods in New England are continuously sheathed wood structural panels, gypsum board, and portal frames around garages.
Continuously sheathed wood structural panels (CS-WSP):
To simplify things, this is just the exterior sheathing on the home, often floor-to-ceiling plywood or OSB sheets with a specific thickness and structural rating. Areas with windows, doors, or other types of penetrations often do not account toward the braced wall design. Certain blocking and fastening are outlined in the IRC, but this type of construction is standard with most framers.
Gypsum Board (GB):
When the exterior walls are not enough to resist the horizontal loads themselves, the interior walls may count toward the design. These are often finished with gypsum board and floor-to-ceiling without openings between. The material is not as strong as plywood or OSB sheathing and, therefore, the length necessary for a GB braced wall is typically more than a CS-WSP.
Portal Frames at Garages (PFG):
When there are large openings, such as garage doors, a portal frame may be the best solution. This type of detail has specific dimensions for the header, the sheathing, fastening, anchors, and much more. Similar to CS-WSP and GB braced walls, portal frames has its limits as to when it can be installed.
What if I can’t meet the requirements of the code?
The IRC requires certain braced wall lengths to withstand certain lateral loads based on the layout of the building and the calculated lateral forces applied to it. If these requirements can be met, the building can be constructed primarily in wood, which is often preferred.
If the requirements cannot be met, custom engineering may be required. This can require custom steel frames or proprietary systems, such as Simpson Strong-Walls or Strong-Frames. In either case, specific structural engineering is required for these types of designs.
If you need a braced wall design or custom lateral force resisting structural elements, Team Engineering can help. Give us a call today to chat with one of our licensed Professional Engineers.