As of Spring of 2006, the City and County of Denver has been requiring a separate shoring permit for all projects where the descending slope of the excavation is steeper than 1:1.
This essentially means that if you are proposing a full basement approximately 9 feet deep, and you want to avoid any shoring, then the footprint of the home must be 9 feet from the property line in order to achieve the 1:1 slope. The City has provided an alternate benching detail that can provide up to 3 feet back in that distance, reducing it to approximately 6 feet total. Regardless, if you have a 5 foot setback and you’re building to it, you will be required to have an engineered shoring design prepared and permitted before you can permit the structure. There is one exception that they allow, and that is if you have soils that would allow a steeper excavation slope. If you go this route, the soils engineer will have to approve it and the City will require a bond to be posted until the excavation is backfilled.
So, what is shoring? Shoring is a general term describing any kind of structural retaining system to keep the vertical wall of soil in a deep excavation from caving in. In the context of the projects in Denver, the most commonly used shoring technique is typically an engineered grid of concrete piers that are drilled and poured in place before the basement excavation takes place. The number of piers, their sizes and locations are based on the depth of the cut, the distance to the property line, the type of soil to be retained and anticipated lateral loads. After the piers are drilled and poured, the hole can be dug right up to the piers, exposing one side of them in the excavation. Then after the foundation work is complete, the structure is backfilled and the shoring just remains in place underground. One important note in the shoring design is that you must anticipate the location of any window wells as these can often be in conflict with the location of the piers. Utility runs also need to be anticipated as well.
So why is all of this required now? Well, obviously, a cave in is a life-safety concern for anyone near the excavation, but it is also a cause for concern with adjacent property damage. For example, if an 8′ cave-in occurs within 5′ of a neighbors garage footing, you can imagine the extent of damages. So, while the shoring requirements add cost to the excavation and foundation requirements for homes with full basements, the intent is to maintain safety and preserve property by reducing the risk of these kinds of damages. We have been successful in negotiating with the City in certain circumstances where the only risk is a sidewalk or some landscaping. In those cases, they required a bond to the value of the improvements that was returned after the work was done and proof that the improvements were preserved in their entirety.
The engineers at EVstudio value engineer the shoring requirements just as we value engineer the structures for the buildings we design, so if shoring is required on your project, we can discuss several paths to satisfy the City requirements that make the most sense for your project and your pocketbook. Our engineering department will gladly work with you on any kind of structural project, so if you find yourself in a situation where you think you may need us, give us a call and we’ll be happy to discuss your options with you.