06 Jan Retaining Walls: How to Build a Retaining Wall | Design, Construction, and Maintenance

The Ultimate Guide to Retaining Walls: 5 Points for Successful Design, Construction, and Maintenance
Retaining walls are essential structures in landscaping and construction, designed to hold back soil and create level areas in sloped terrain. This comprehensive guide will explore the various types of retaining walls, their design considerations, construction techniques, and maintenance requirements. Whether you’re a homeowner or a professional, understanding these key aspects will help you create durable and effective retaining wall solutions for your property.
What are the different types of retaining walls?
Understanding gravity retaining walls
Gravity retaining walls are one of the most common types of retaining walls. These structures rely on their own weight and mass to resist the lateral pressure of the soil behind them. Gravity walls are typically constructed using heavy materials such as concrete blocks, stone, or masonry. The wall’s stability is achieved through its sheer weight, which counteracts the force of the earth it’s holding back. Gravity walls are particularly effective for shorter heights, usually up to 3 meters, and are often used in residential landscaping projects.
When designing gravity retaining walls, it’s crucial to consider the soil type and pressure behind the wall. The wall’s thickness and height must be carefully calculated to ensure it can withstand the force exerted by the backfill. Proper drainage is also essential to prevent water buildup behind the wall, which can lead to increased pressure and potential failure. Gravity walls can be constructed with a slight backward lean or batter to improve their stability and resistance to overturning forces.
Exploring reinforced retaining walls
Reinforced retaining walls are a more advanced type of retaining wall system that incorporates additional structural elements to enhance stability and support. These walls typically consist of a facing material, such as concrete blocks or precast panels, combined with reinforcing elements that extend into the backfill soil. The reinforcement can be in the form of geogrid, steel bars, or soil nails, which work together to create a composite structure capable of withstanding greater lateral earth pressures.
One popular type of reinforced retaining wall is the cantilevered retaining wall. This design uses a reinforced concrete stem and base slab to form an L-shaped structure. The weight of the soil on the base helps counteract the overturning forces, allowing for taller and more slender walls compared to gravity walls. Reinforced retaining walls are ideal for situations where space is limited or when dealing with challenging soil conditions. They can be designed to accommodate surcharge loads from nearby structures or slopes, making them versatile solutions for various landscaping and construction projects.
Comparing timber retaining walls vs. other materials
Timber retaining walls are a popular choice for many homeowners due to their natural appearance and cost-effectiveness. These walls are typically constructed using treated lumber or railway sleepers, which are stacked and secured with stakes or posts. Timber retaining walls work well for low to moderate heights and can be an excellent option for creating terraced gardens or managing small slopes. However, it’s important to note that timber walls have a shorter lifespan compared to other materials and may require more frequent maintenance.
When comparing timber retaining walls to other materials like concrete or stone, several factors come into play. Concrete block retaining walls offer greater durability and can be designed for taller heights, making them suitable for more challenging applications. Stone retaining walls provide a timeless aesthetic and can be built as either dry-stacked or mortared structures. While timber walls may be more budget-friendly initially, their limited lifespan and potential for rot or insect damage should be considered. Ultimately, the choice between timber and other materials depends on factors such as the wall’s height, soil conditions, aesthetic preferences, and long-term maintenance considerations.
How do I build a retaining wall that lasts?


Essential steps for proper retaining wall construction
Building a retaining wall that lasts requires careful planning and execution. The first step is to assess the site conditions, including soil type, drainage patterns, and slope angle. This information will help determine the appropriate wall design and construction method. Next, excavate the area and create a level base for the wall’s footing. The footing should be wider than the wall itself and extend below the frost line to prevent shifting. For walls over 1.5 metres in height, it’s crucial to consult with a structural engineer to ensure proper design and compliance with local building codes.
When constructing the wall, start by laying the first course of blocks or materials on the prepared base. Use a level to ensure each course is straight and even. As you build up the wall, incorporate proper drainage systems, such as gravel backfill and perforated pipes, to prevent water accumulation behind the wall. For taller walls, consider using geogrid reinforcement to enhance stability. Pay attention to the wall’s batter or slight backward lean, as this helps counteract soil pressure. Finally, cap the top of the wall to protect it from water infiltration and provide a finished appearance. By following these essential steps, you can build a retaining wall that will stand the test of time.
Choosing the right materials for your retaining wall
Selecting the appropriate materials for your retaining wall is crucial for its longevity and performance. The choice of materials depends on factors such as the wall’s height, soil conditions, aesthetic preferences, and budget. Concrete blocks are a popular option due to their durability and ease of installation. They come in various sizes and textures, allowing for customisation to match your landscape design. Natural stone offers a timeless appeal and can be used for both dry-stacked and mortared walls, though it requires more skill to install properly.
For those seeking a more eco-friendly option, timber retaining walls can be constructed using treated lumber or railway sleepers. While timber walls have a shorter lifespan, they blend well with natural surroundings and can be an excellent choice for low to moderate height walls. Gabion walls, which consist of wire cages filled with rocks, provide a unique aesthetic and are particularly effective in areas prone to erosion. When choosing materials, consider their durability, maintenance requirements, and compatibility with the surrounding landscape. It’s also important to factor in the wall’s structural needs, such as the ability to incorporate reinforcement or drainage systems, to ensure long-term stability and performance.
Importance of drainage in retaining wall design
Proper drainage is a critical aspect of retaining wall design and construction. Without adequate drainage, water can accumulate behind the wall, leading to increased hydrostatic pressure and potential failure. To prevent this, incorporate a drainage system that includes a layer of gravel backfill behind the wall. This gravel layer acts as a filter, allowing water to flow freely while preventing soil particles from clogging the system. A perforated drainage pipe should be installed at the base of the wall to collect and redirect water away from the structure.
In areas with heavy rainfall or poor soil drainage, consider using geotextile fabric to separate the gravel backfill from the native soil. This fabric prevents soil particles from mixing with the drainage material, ensuring long-term effectiveness. For taller walls or those in challenging soil conditions, it may be necessary to incorporate additional drainage features, such as weep holes or vertical drainage channels. Regular maintenance of the drainage system, including clearing any debris from the top of the wall and ensuring proper grading around the structure, is essential for maintaining the wall’s stability and longevity. By prioritising drainage in your retaining wall design, you can significantly reduce the risk of water-related issues and extend the life of your wall.
Do I need building consent for my retaining wall project?
Height restrictions and building code requirements
Understanding height restrictions and building code requirements is crucial when planning a retaining wall project. In many jurisdictions, including New Zealand, retaining walls up to 1.5 metres in height generally do not require building consent. However, this can vary depending on local regulations and specific site conditions. It’s important to note that the height is typically measured from the bottom of the wall to the top, including any surcharge or additional load above the wall. Even if your wall falls below the consent threshold, it must still comply with relevant building codes and standards to ensure safety and structural integrity.
Building codes often specify requirements for wall design, materials, and construction techniques. These may include guidelines for footing depth, reinforcement methods, and drainage provisions. For walls exceeding the height limit or those subject to additional loads, such as vehicle traffic or nearby structures, more stringent design and construction standards may apply. In these cases, the involvement of a qualified engineer or architect is often necessary to ensure compliance with building codes. It’s always advisable to check with your local council or building authority to understand the specific requirements in your area, as regulations can vary between different regions and municipalities.
When is a building consent necessary for retaining walls?
Building consent is typically required for retaining walls that exceed certain height thresholds or are subject to specific conditions. In New Zealand, for example, retaining walls over 1.5 metres in height generally need building consent. However, consent may also be necessary for walls of any height if they are supporting a surcharge or additional load, such as a driveway, building, or steep slope above the wall. Walls that are part of a broader landscaping or construction project may require consent as part of the overall development plan.
It’s important to note that even if your retaining wall doesn’t require building consent, it must still be designed and constructed to meet relevant building codes and standards. Factors that may trigger the need for consent include proximity to property boundaries, impact on drainage patterns, and potential effects on neighbouring properties. In some cases, retaining walls may also require resource consent if they are located in environmentally sensitive areas or have significant visual impacts. To ensure compliance and avoid potential legal issues, it’s always best to consult with your local council or a qualified professional before starting any retaining wall project, especially for walls approaching or exceeding the typical consent threshold.


What are the best retaining wall solutions for sloped landscapes?
Designing retaining walls for steep slopes
Designing retaining walls for steep slopes presents unique challenges that require careful consideration and engineering expertise. The primary goal is to create a stable structure that can effectively resist the increased lateral earth pressure exerted by the slope. One effective approach is to use reinforced retaining walls, such as mechanically stabilised earth (MSE) walls, which incorporate geogrid or other reinforcing materials into the backfill. These systems distribute the load over a larger area, enhancing the wall’s ability to withstand the forces acting upon it.
When designing for steep slopes, it’s crucial to conduct a thorough site analysis, including soil testing and slope stability assessments. This information helps determine the appropriate wall height, reinforcement requirements, and drainage needs. Tiered or stepped wall designs can be an effective solution for very steep slopes, as they distribute the load across multiple smaller walls rather than a single tall structure. Incorporating proper drainage systems, such as chimney drains or horizontal drains, is essential to manage water flow and reduce hydrostatic pressure behind the wall. For complex slope situations, consulting with a geotechnical engineer is highly recommended to ensure the retaining wall design adequately addresses the specific challenges of the site.
Terracing options for challenging terrain
Terracing is an excellent solution for managing challenging terrain and creating usable space on steep slopes. This approach involves constructing a series of level platforms supported by retaining walls, effectively transforming a steep hillside into a series of flat areas. Terracing not only provides functional space for gardening, landscaping, or outdoor living areas but also helps control erosion and manage water runoff. When designing terraced retaining walls, it’s important to consider the overall slope angle, soil conditions, and desired terrace depth to determine the appropriate number and height of walls.
There are various terracing options available, depending on the site conditions and aesthetic preferences. Gravity walls, such as dry-stacked stone or interlocking concrete blocks, can be effective for low to moderate height terraces. For taller terraces or those subject to greater soil pressure, reinforced walls or cantilevered designs may be necessary. Incorporating proper drainage between each terrace level is crucial to prevent water accumulation and ensure long-term stability. Consider integrating staircases or pathways between terraces to improve accessibility and create a cohesive landscape design. By carefully planning and implementing a terraced retaining wall system, you can transform challenging terrain into a functional and visually appealing outdoor space.
How can I maintain my retaining wall for long-term stability?
Regular inspection and maintenance tips
Regular inspection and maintenance are crucial for ensuring the long-term stability and performance of your retaining wall. Conduct visual inspections at least twice a year, preferably in spring and fall, to identify any signs of damage or potential issues. Look for cracks, bulges, or leaning in the wall structure, as these may indicate underlying problems. Check for any erosion or soil movement behind the wall, which could compromise its stability. Inspect the drainage system, including weep holes and pipes, to ensure they are clear of debris and functioning properly.
Maintenance tasks should include clearing vegetation growth near the wall, as roots can cause structural damage over time. Trim plants and remove any trees growing too close to the wall. Clean the wall surface periodically to remove dirt, algae, or stains, using appropriate cleaning methods for the wall material. For timber retaining walls, check for signs of rot or insect damage, and apply wood preservatives as needed. If you notice any significant issues during your inspections, such as large cracks or substantial movement, consult a professional immediately. By implementing these regular inspection and maintenance practices, you can address minor problems before they escalate and extend the lifespan of your retaining wall.
Addressing common retaining wall issues
Retaining walls can develop various issues over time, but many can be addressed with proper care and timely intervention. One common problem is water-related damage, often caused by inadequate drainage or clogged weep holes. To address this, ensure that the drainage system is clear and functioning correctly. Clean out weep holes and consider installing additional drainage measures if needed. Soil erosion behind the wall can lead to instability; combat this by maintaining proper grading and vegetation cover above the wall to control runoff.
Cracks in the wall may occur due to settling or excessive pressure. Small cracks can often be repaired with appropriate fillers or sealants, but larger cracks may require professional assessment. If you notice the wall leaning or bulging, it’s crucial to address this promptly as it could indicate a more serious structural issue. In some cases, reinforcement or rebuilding parts of the wall may be necessary. For timber retaining walls, rot and insect damage are common concerns. Replace any severely damaged timber and treat the wood with preservatives to prevent further deterioration. By addressing these common issues promptly and effectively, you can maintain the integrity and appearance of your retaining wall, ensuring its continued functionality in your landscape.


What are the key factors in retaining wall design?
Considering soil type and pressure in wall design
Soil type and pressure are critical factors in retaining wall design, as they directly impact the wall’s stability and load-bearing capacity. Different soil types exert varying amounts of pressure on the wall, with cohesive soils like clay generally exerting less pressure than granular soils like sand. Conducting a thorough soil analysis is essential to determine the soil’s properties, including its angle of internal friction, cohesion, and unit weight. This information helps engineers calculate the lateral earth pressure that the wall must resist and design an appropriate structure to withstand these forces.
In addition to soil type, factors such as groundwater conditions, surcharge loads, and slope angle above the wall significantly influence the pressure exerted on the retaining structure. Proper drainage design is crucial to minimise hydrostatic pressure behind the wall, which can greatly increase the total load. For walls supporting sloped backfill or subject to additional loads, such as vehicle traffic or nearby buildings, these surcharge pressures must be accounted for in the design. By carefully considering soil type and pressure in the design process, engineers can create retaining walls that effectively resist lateral forces and maintain long-term stability, ensuring the safety and functionality of the surrounding landscape.
Calculating proper wall height and thickness
Calculating the proper wall height and thickness is a crucial aspect of retaining wall design that requires careful consideration of various factors. The wall’s height is typically determined by the site’s topography and the desired grade change, while the thickness is influenced by the wall height, soil pressure, and structural requirements. For gravity walls, the rule of thumb is that the base width should be approximately 50-60% of the wall height. However, this can vary depending on the specific design and materials used. As wall height increases, so does the need for a wider base or additional reinforcement to ensure stability.
When calculating wall thickness, engineers must consider the lateral earth pressure, potential surcharge loads, and the wall material’s properties. For reinforced concrete walls, the stem thickness is often determined based on the bending moments and shear forces acting on the wall. The use of steel reinforcement allows for thinner wall designs while maintaining structural integrity. For segmental retaining walls using interlocking blocks, the block size and configuration, along with any geogrid reinforcement, determine the effective wall thickness. It’s important to note that local building codes and engineering standards may specify minimum thickness requirements for different wall types and heights. Proper calculation of wall height and thickness is essential for creating a stable, durable retaining wall that meets both functional and safety requirements.
Incorporating aesthetic elements into functional design
Incorporating aesthetic elements into functional retaining wall design is essential for creating structures that not only serve their purpose but also enhance the overall landscape. One approach is to select materials that complement the surrounding environment, such as natural stone for a rustic setting or sleek concrete blocks for a modern look. Varying the texture, colour, or pattern of the wall face can add visual interest and help the wall blend seamlessly with its surroundings. For instance, using a combination of different sized blocks or incorporating a random ashlar pattern in stone walls can create a more dynamic and appealing appearance.
Another way to enhance the aesthetic appeal of retaining walls is by integrating planting pockets or terraces into the design. This allows for the incorporation of vegetation, softening the wall’s appearance and creating a more natural look. Steps or seating areas can be built into the wall structure, adding functionality while creating interesting focal points. Lighting elements, such as recessed LED fixtures or up-lighting, can be incorporated to highlight the wall’s texture and create dramatic effects at night. By carefully balancing aesthetic considerations with structural requirements, it’s possible to design retaining walls that not only effectively manage terrain but also serve as attractive landscape features that enhance the overall property value and visual appeal.
Conclusion
In conclusion, retaining walls are an excellent solution for managing soil and creating level areas, playing a critical role in landscaping by preventing soil from sliding. There are various types of retaining walls, such as timber pole, crib walls, and gabions, with anchored walls being ideal for taller structures. Proper design is essential for stability and durability, considering factors like design life and local regulations outlined in government regulations.
NZCCS provides expert solutions for retaining walls to help you create stable and visually appealing landscapes. Whether you need a wall for functionality or aesthetics, proper engineering is vital, especially for structures several metres high. Retaining walls often require drainage systems and other features for optimal performance. From concrete to natural materials, NZCCS can guide you in choosing the best solution for your needs. Contact NZCCS today to discuss your project and ensure a professionally built retaining wall that lasts.