Most homes here in San Francisco are built from locally forested redwood lumber with little to no insulation, lath and plaster walls and ceilings, and foundations without reinforced concrete. These simple materials used in building beautiful homes from Victorian to mid-century has certain drawbacks to today’s standards for health and safety. In retrospect, we should give credit to the craftsman, architects, engineers, and regular homeowner builders for doing the best they could given the supplies they had at their disposal (however, violations of building codes and lack of building knowledge should not go unnoticed which happened back then as it does now). Today’s concerns are the use of lead in building materials from plumbing to painting as well as the use of asbestos from ductworks to insulation.
Here is a 2x6” redwood framing with exterior siding. This the ground floor garage of a 1916 three story Edwardian home. Notice the horsehair lath and plaster on the ceiling. It was tested negative for asbestos just in case due to rewiring, installing a new ductwork, and a new gas line.
In this topic I examine the use of seismically retrofitting the ground floor of a three story Edwardian home.
Know Your Wood
There was evidence of termite infestation in the crawlspace, most of the studs that held up the house were of the Red Cedar specie — which is great as an exterior siding, but can be susceptible to termites that live in the Bay Area.
Replace Compromised Studs
In this case, I added redwood to replace the red cedar. Plentiful locally, redwood is a great deterrent against insects such as termite infestations and fungi as it contains a chemical agent called tannin, which gives off its reddish hue. Notice the hold downs are situated on the flat step and end of the foundation.
Stepped Foundation
Here is a schematic I did on SketchUp to represent the stepped foundation similar to the house I was working on.
When constructing a building with a stepped foundation, it is essential to ensure that the hold downs are placed at the same height across the different levels. By aligning the hold downs at the same height, you can maintain the structural integrity of the building and evenly distribute the loads to the foundation.
Having hold downs at consistent heights is crucial for providing adequate support and stability to the structure. It helps prevent uneven stress distribution, which can lead to structural issues over time. Additionally, uniform hold down placement simplifies the construction process and ensures a more cohesive and reliable foundation system.
By paying attention to the alignment of hold downs on a stepped foundation, builders can enhance the overall strength and durability of the building. This meticulous approach to construction will help create a sound infrastructure that can withstand various external forces and provide long-lasting protection for the occupants.
Blocking
I installed blocking so that the edge of each plywood can be nailed and further strengthen the lateral forces of the vertical studs to prevent a domino effect.
The sill plate, located between the foundation and studs that fastened on top of it, tend to be wider than the studs itself. This poses a problem in seismic retrofits because you would ideally want the bottom of the plywood to be fastened to the sill plate so that the concentric forces during an earthquake can transfer back down to the ground.
In the photo above they concealed the sill plate with the foundation. Since this was a voluntary seismic retrofit, I added blocking at the base of the foundation to act as my sill plate. Each blocking was glued down and fastened with three structural screws. Every 4 to 6 feet had new 5/8” anchor bolts, even though there were existing anchor bolts.
Overall the idea was that the new blocking will act as my continuous sill plate for the plywood.
Insulation
Either side of the wall received proper insulation before covering it up with plywood. This will reduce exterior noise and prevent infiltration of cold and damp air.
Consider insulating and getting all wiring and plumbing done before you seismically cover the walls with plywood.
Staggered Plywood
I chose to stagger my plywood sine this was on a stepped foundation. The plywood covers both side of the home and into crawlspace.
Upgrade Your Home with Seismic Retrofitting and Shearwall Installation
Is your ground-level home prepared for the unexpected? At Viking Wood, we understand the importance of ensuring your home's structural integrity, especially in areas prone to seismic activity. Retrofitting your home with a shearwall is a wise investment that can enhance its resistance to earthquakes and provide you with peace of mind.
Why Choose Seismic Retrofitting and Shearwall Installation with Viking Wood?
Safety First: Protect your loved ones and belongings by fortifying your home against seismic forces.
Expertise: Our team of experienced professionals specializes in seismic retrofitting, ensuring the job is done with precision and care.
Quality Materials: We use high-quality wood and construction materials to guarantee the durability and longevity of your shearwall.
Peace of Mind: With a properly retrofitted home, you can rest easy knowing that your property is better equipped to withstand seismic events.
Don't Wait Until It's Too Late
Take proactive steps to safeguard your home today. Contact Viking Wood to schedule a consultation and learn more about how seismic retrofitting and shearwall installation can benefit your ground-level home. Upgrade your home with Viking Wood, because your safety is our priority.