The top 3 methods used to retrofit "soft story" buildings.
Three Retrofit Construction Methods & How it Affects Costs
If you own a rental property in Los Angeles it’s likely a soft-story. They are hard to avoid in Southern California, it’s the typical apartment building that has parking directly underneath the apartments. You may have received an Order to Comply (or “OTC”) letter from the City of Los Angeles, Santa Monica, or West Hollywood notifying your building requires a Soft-Story retrofit. Knowing that your property does not comply with the latest retrofit ordinances can give you some anxiety, but not knowing how much a retrofit can cost will give you insomnia. You are not alone, the Los Angeles Department of Building and Safety (or “LADBS”) identified over 15,000 buildings that will need some type of retrofit work. LADBS notified all of the property owners to start the process of gaining compliance within the first two years. Our team has analyzed dozens of retrofit engineering plans created by the best Structural Engineering firms in California, and we learned two things. The construction drawings clearly showed that a soft-story building can be retrofitted using three different construction methods, and no two buildings are the same no matter how similar they might look. We collaborated with these structural engineering firms to provide construction quotes for the property owners and noticed that all the projects landed within distinct price points, depending on the retrofit solution. In this article, we will analyze the three most common methods to retrofit a building and will examine the prices of each.
(Diagram of moment frames in a soft-story retrofit)
It is important to understand that the purpose of a soft-story retrofit is to strengthen a structure to resist lateral loads (the shifting of the building on a horizontal plane) experienced during seismic activity. During an earthquake, the structure will move from side-to-side in an oscillating motion. As an earthquake continues, top-heavy buildings begin to sway violently and develop enough kinetic energy at their top section to collapse. The retrofit is designed to create sufficient resistance to withstand this type of movement and prevent a catastrophic collapse. The amount of resistance needed is factored using three distinct variables; how much the building weighs, the distance to the closest fault line, and the highest hypothetical magnitude the fault line can experience. There are three main types of soft story-retro fit methods – let’s take a look at them below
Plywood Shear Walls
(Shear wall resisting lateral forces)
This type of structural wall helps strengthen the entire structure to prevent movement during seismic events. Although a simple solution, shearing a structure with structural plywood strengthens the entire building, preventing the collapse of the structure during the lateral forces experienced during major earthquakes. Normally during an earthquake, the walls will move laterally, and if the seismic movement is great enough the structural connections can separate. The reinforced shear walls prevent the walls from separating and causing a collapse. This image below shows how lateral forces during an earthquake affects a wall. These are the same forces that will impact your homes and your rental properties.
Pre-Fabricated Shear Wall System
There are two distinct types of shear walls, plywood shear walls, and pre-fabricated steel shear walls. Simpson Strong-Tie and MiTek Industries manufacture shear wall panels that can help add shear value to any structure. These pre-fabricated walls come with load ratings and specifications provided by the manufacturer. One benefit of steel shear wall panels is that they have more lateral resistance than regular plywood shear walls. This is a good retrofit solution for parking areas that have a low clearance, this solution will ensure that tenant parking is not impacted during construction. Tenants can get pretty upset if they lose parking for a couple of months. Pre-Fabricated Panels come in various sizes and are priced between $350 and $600 per panel, a pretty affordable retrofit solution. Plywood shear walls are even more affordable with a material cost of approximately $250 including all necessary hardware. But although these solutions are affordable, these savings can be deceiving because installation times are dramatically different. Installing plywood shear walls can cost almost twice as much. Installing a 12-foot plywood shear wall may take two-man crew two days to complete. A steel shear wall of the same size will only take a two-man crew one full day to install.
In the Hardy Panel diagram below, you can see how a 9 foot Hardy Panel from MiTek USA can replace the shear value of a 6 foot wall. This type of product can be used to gain shear strength on draglines where you don’t have enough wall space to create the seismic resistance necessary. This is a good solution for older buildings that have low clearance or parking areas that are below grade. The prefabricated panels are installed with a bolting kit that connects to a grade beam, both of these elements work together to create a bigger frame. A grade beam is a subterranean concrete beam that is reinforced with heavy rebar. The two posts or columns connect to create lateral resistance. In the image below you can see a large rebar cage that will be filled with concrete to create a grade beam.
The cost of a retrofit project using plywood shearing versus a pre-manufactured steel shear wall can vary. But on a small soft-story building you can expect to pay the following prices. A 12-foot plywood shear wall can cost about $3,000 including labor and materials. Using a premanufactured shear wall like the Hardy Frame from MiTek USA can cost about $2,650 in labor and materials. We do urge you to keep in mind that a soft-story retrofit project has other costs like demolition, excavation, concrete pours, and stucco repair. Utilizing shear walls for a soft-story retrofit can cost as low as $20,000 or as high as $40,000. But keep in mind this solution is best for smaller buildings or large buildings with a small overhang. Do not expect to use this solution on a 25-unit apartment complex.
Steel Cantilever Column System
(Retrofit using cantilever I-Beam)
Cantilever I-Beams are widely becoming the preferred method for retrofitting soft-story buildings. I recently attending the Structural Engineering Association of California convention in Palm Desert, where I attended a couple of seminars retrofitting seminars. I encountered a few speakers that had some dissenting views on this method of soft-story retrofit design. Their critiques were focused on the level of stress and distortion that I-Beams experience during a seismic event. If an I-Beam is damaged during an earthquake, the entire beam must be removed and replaced. Ideally, the entire system, including grade beams, should be replaced. You can see the installation of new cantilevered I-Beams in the picture below.
Currently, the city of Los Angeles and Santa Monica allow this method of construction as a lower-cost design option. On a small soft-story project you can expect to pay around $35,000 using a cantilever I-Beam. A larger soft-story building with two or more stories will cost anywhere between $65,000 to $75,000 to retrofit using these methods.
Special Moment Frames
Special moment frames are the most common retrofit solution. They are available in a wide variety of sizes and from different manufacturers. These systems can be delivered assembled or flat shipped. Without including installation, the cost for special moment frame varies between $8,500-$10,000 depending on the weight of the steel. Installing the frames is not complicated or time-consuming. But retrofit projects also include cutting concrete and excavation, stucco repair and in some cases removing and relocating plumbing lines and utility lines.
One of the best moment frame systems we have seen is a bolted system from Simpson Stong-Tie, their Strong-Frame is sectional and is bolted. This allows it to be easily repaired if damaged during an earthquake. Simpson Strong-Frames are the only Special Moment Frames that are designed to be reused after an earthquake. They have a specially designed yielding that resembles a fuse, this link absorbs all the shock and damage of the earthquake. This is an extraordinary product that I recommend to the majority of my customers. Special Moment Frames are best suited for large and heavy buildings that need serious reinforcement. If your project requires a retrofit solution that utilizes special moment frames you can expect to pay as little as $70,000 or as much as $110,000 depending on the size and number of the moment frames. If you want to learn more about Simpson Strong-Frames and Moment Frames in general, you can read my article “An Honest Comparison” by clicking here. You can read more about Moment frames by following this link.
Findings & Recap
Each retrofit solution featured in this article accomplishes the same goal, they add reinforcement to a structure so it can survive seismic movement. Each building is a different and careful consideration should be taken when considering which retrofit method or combination of methods will be used on a retrofit. If money is your biggest concern, we suggest considering a combination of cantilever I-Beams and Shear Walls as a retrofit solution. But you should also consider the costs of labor. The only exception would be if the labor to install hold downs and other plywood shear walls cost more than the installation of a Special Moment Frame and grade beam. This method is stronger and may be preferable to strength a long wall with a heavy load on it.
Special Moment Frames are currently the most expensive construction method for soft-story retrofits. But as the saying goes “you get what you pay for”, special moment frames are the best retrofit solutions available in the market today. If damaged, it can be easily repaired or replaced and can essentially last a lifetime. No other system offers that feature. Utilizing moment frames on your soft-story retrofit project can help you save on other types of labor like welding. These retrofit construction methods and pricing discussed in this article are meant to inform property owners what different retrofit methods can cost. Property owners should closely consider the reputation of the contractor and not solely on the estimated price of the remodel. Please contact or office to properly assess the cost of your specific building.
Want to Learn More?
If you want to learn everything there is to know about soft-story retrofits you'll want to check out our most in-depth article What is a Soft-Story Retrofit? Everything You Need to Know About Retrofits on our new website. There, you'll be able to access all of our retrofit blog articles, case studies, our retrofit gallery, short videos, and enjoy free access to our full-length soft-story webinars. Our team has developed all this content for property owners like you. It is your destination to learn all about the retrofit process. Bay Cities Construction and Soft-Story Retrofit Pros is here to help answer any questions you may have about your retrofit project. Our team has the experience to Engineer & Build a Cost-Effective Retrofit Solution for your property. Get started today by visiting our website at www.softstoryretrofitpros.com to schedule a free assessment.
For over 15 years Soft-Story Retrofit Pros has helped hundreds of homeowners with their projects. When you hireRetrofit Pros you don’t just hire a contractor, you hire an entire team of Pros. With several years of experience, our team has the expertise to help you Design, Engineer, and Build Your Retrofit Solution. We also represent you City Representation when submitting your plans and ensuring they are approved, and we handle all the Permit Processing so you never miss a day of work. If you think Retrofit Pros is the right team for you, contact us today. We have the experience, knowledge, and know how to help you save time & money on your seismic retrofit.
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