Does your garden have slopes, slopes, and slopes? Then you will likely have a spare wall somewhere on your property. Used everywhere from highway construction to landscaping, retaining walls prevent ground that would otherwise erode or collapse. Homeowners often rely on retaining walls to keep the soil stable in raised yard features, but they can also use man-made structures when planting tiered gardens on a sloping area of the yard, controlling erosion on the slope, or creating a raised seating spot. If you are considering building a retaining wall, here is everything you need to know about supporting structures.
The basics of retaining walls
Retaining walls have a variety of uses around the yard, all of which include preventing the ground from spilling off a steep slope. They are indispensable in creating sunken patios, basements, and any other solid space with abrupt ground elevation separation. You’ll also find retaining walls in parks and gardens, where they act as hedges for plants, statues, and decorative landscaping elements.
Retaining walls are often built with concrete, stone or brick. But, if you’re looking to do a do-it-yourself job, retaining wall blocks (available at most home improvement stores) are your best bet. These blocks cost between $1.25 and $4 per block, depending on their size and texture, and feature locking edges that hold each row of blocks together. A small retaining wall less than three feet high will cost on average $5 to $8 per square foot, if you build it yourself. Larger retaining walls, which are not DIY-friendly, are more expensive due to the labor costs involved. A natural stone retaining wall or brick laid by a builder can cost upwards of $20 per square foot, and a cast concrete retaining wall will set you back $13 to $18 per square foot. The contractor may also charge more labor and materials if they have to pour a deep frost base (described below) or remove tree roots that get in the way of the foot.
If you plan to build a retaining wall, check in advance with your local building authority. Retaining walls can alter the flow of water and affect your neighbors, so you may need to obtain a zoning permit or a building permit. Local building codes and ordinances vary between communities, so don’t skip this step. You will also need to call DigSafe (811) to get representatives from the local utility companies to come out and check if there are any buried electric lines in the way.
Create a retaining wall
If you are planning to build a retaining wall, consider the following factors related to support, foundation, backfill, and drainage.
Find trusted local professionals for any home project
When building a retaining wall, landscapers often tilt it slightly toward the land it contains. This design, known as ‘graded masonry’, creates a strong wall structure that pushes back against the lateral pressure of the soil behind it. Back walls can be built by anyone with a strong background and basic knowledge of construction, as long as they contain blocks designed to hold the wall set.
Some types of retaining walls require additional structural support to prevent them from tipping over. This includes vertical walls that do not slope toward the existing ground, as well as walls more than three feet high. Depending on the height of the wall and the pressure of the ground behind it, additional supports can be in the form of buried plinths, steel stiffeners, a cantilever design, or back ties that extend deep into the ground behind the wall and connect to buried anchors called “dead”. You can also add extra strength by using a “gravity wall,” which is so wide that its weight acts as a support against the pressure of the soil behind it. This type of wall is not popular because it requires a large amount of stone or concrete for construction.
The gravel-filled trench provides a suitable foundation for a short retaining wall graded three to five courses (each layer of blocks is called a “course”). A buried structural base is usually required for larger retaining walls. To create this, the landscaper pours concrete below the frost level (the depth at which the ground will freeze during the winter). Legs that are poured shallowly are more likely to shift and move if the moisture in the soil freezes and rises. Since frost levels vary from region to region, contact your local building authority for details before building a large retaining wall.
The space behind a newly constructed retaining wall should be filled with gravel or sand – not dirt. Dirt absorbs water and swells when saturated, which puts unwanted pressure on the back of the wall. Meanwhile, gravel and sand do not swell or retain water, so the wall will be subjected to less pressure. This reduces the risk of cracks and damage.
Stackable retaining block walls with gravel or sand backfill usually do not have drainage problems, as water seeps through the backfill and drains between the individual blocks. But if you have a solid retaining wall, such as a concrete basement wall, conditions must be put in place to drain water (or it may pool behind the wall and cause a crack). Many landscape architects choose to install drain tile, which transfers groundwater to outlets where it can drain harmlessly.
DIY Retaining Wall Tips
When building a retaining wall, follow these tips for better building and strong supports.
- Choose materials that you can work with easily. If you do not have experience with structural support, wall blocks are your best bet. It is also widely available at most home centers.
- To prevent the bottom row of blocks from being pushed out, bury the bottom of the retaining wall. The general rule is to bury about one-eighth of the height of the wall. For example, if your wall is three feet (36 inches) tall, you should start the first cycle of blocks five inches below soil level. The gravel base should start three inches below this.
- For best results, make sure the first cycle of blocks is completely level. If it is unbalanced, then your entire end wall will also be unsuitable.
Find trusted local professionals for any home project