Retaining walls are commonly placed along property lines. Since we all like to maximum our property, you probably want to install the fence as close as possible to the retaining wall. But before you grab the post hole diggers, let’s go over a few important things to consider.
Important Info
Many jurisdictions require a permit for installing a fence. Your city will want to inspect the fence construction or they may have restrictions for building within an easement. A fence typically has a minimum offset from the property line, unless both property owners agree to have it placed on the property line. The city also wants to ensure a fence will not negatively affect another structure, such as a retaining wall.
For non-engineered walls, the edge of the fence foundation must be placed at least 3-ft from the back of the retaining wall. By edge of the foundation, this means the edge of the hole and edge of the concrete placed around the post. The 3-ft minimum offset is required by the International Building Code. This ensures there is enough room to distribute the load from the fence so that it will not negatively affect the retaining wall. If you are required to file a permit to build the fence, you must demonstrate that the fence is at least 3-ft away from the edge of the retaining wall or that the wall is engineered for a fence.
Fences impose a surcharge on the wall. You may not realize it, but the wind from mild storm blowing on a fence can create over 500 lbs of force at each fence post! That is more than enough to destroy an entire retaining wall. If placing the fence 3-ft behind the wall is not ideal, there area a few additional options.
Sleeve-It System
The Sleeve-It* system is a pre-engineered product developed to take all the load from a fence so that it does not affect a retaining wall. The Sleeve-It system is designed for a 5-ft post spacing. During construction, install a Sleeve-It unit directly behind a retaining wall at each post location. After the wall is constructed, remove a perforated lid to insert the fence post. Once the post is straight, fill the remaining void with concrete.
These units are advertised for segmental block retaining walls, but they can be used behind any retaining wall type. You can download the full installation guide here.
Installing a Fence Directly on Top of Wall
Unless specifically designed by an engineer, installing a fence directly on top of a retaining wall is not recommended. As described above, the wall must be designed to handle over 500 lbs of force at each fence post. Segmental retaining wall blocks cannot handle that load on their own, hence why the Sleeve-It system is recommended if the 3-ft minimum offset cannot be achieved. No amount of adhesive between the blocks can account for the fact that a 75 lb or less retaining wall block cannot resist a 500 lb lateral load.
Wood retaining walls must be specifically designed by an engineer to accommodate a fence on top. This will typically include a specialized tie back or cantilever at each fence post location.
Stone walls are all unique. It may be possible to core through the top of a stone wall to install a fence post. The stones must be large enough, the wall thick enough, and structural grout installed between each stone. Only an engineer can determine this.
Concrete retaining walls can be designed for a fence to sit directly on top of the wall. Concrete walls are constructed of either concrete masonry units (CMU’s or cinder blocks) or poured concrete. The concrete wall must have steel reinforcing installed that strong enough to handle the added load. All concrete retaining walls must have a footing that is properly size to handle all loads on the wall, including a fence. Only an engineer can properly size the reinforcing steel and footing to handle a fence. The fence post may be embedded in the concrete or attached with brackets after the wall is built.
Final Thoughts
We all want to maximum the space on our property. If placing a fence a minimum of 3-ft behind a retaining wall is not an option, use the Sleeve-It* system or check out our services to explore additional options.
After checking with your city, remember to call 811 or visit call811.com. This free service will notify your utility companies to come out and mark any utility lines near your project.
*Amazon Affiliate – If you use these links and make a purchase, I may be compensated.
It’s nearly impossible to find knowledgeable people in this particular topic, but you seem like you know what you’re talking about! Thanks