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Retaining Walls & Blocks

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Retaining Walls for Your Property

Retaining walls add to the exterior appeal of your home or business. They also are important for protecting your buildings and property from damage due to storm water drainage.

Image of water draining away from the foundation of a building. Underground Landscaping can repair and rebuild a retaing wall to protect your property.

Control Water Run-off

The force from huge rainfalls or spring thaws can cause lots of damage by itself. In addition, the water pools around foundations and structures and causes clogs in drainage systems when left to itself. Proper landscaping and the use of retaining walls can slow it down, spread it out and control where it ends.

Image of a retaining wall. Retaining walls are excellent landscaping ideas. By putting in a wall on a slope it helps to control the flow of storm water down a slope and creates a level space to introduce plants or a rock garden. Great landscaping idea.

Create Usable Space

Who likes to mow the lawn on a hill? Some are steep enough that one needs to be careful using a riding mower. Introducing a retaining wall on the hill provides a level place that helps control drainage and opens up space for beautifying your property with a small garden or even a patio area complete with firepit and barbeque.

Image of plants near foundation that have suffered from water run-off. Retaining walls protect a building by controlling how storm water is distributed and drains away during and after a storm.

Avoid Soil
Erosion

Soil erosion has occurred from the beginning of time everywhere that water runs downhill. Top soil is the richest for plant vegetation, which also helps trees and plants to root and to hinder soil erosion even more. Topsoil is the most exposed to the wind and rain. Retaining walls help control how storm waters drain, which helps preserve the top soil for your lawn and gardens.

How Underground Landscaping
Builds a Retaining Wall

Gravity Retaining Wall Requirements

Gravity retaining walls are the most common, especially for walls lower than four feet.
They rely on their own weight to withstand the pressure from the earth to not collapse or overturn.

Prepare and Level a Trench for the Foundation

The foundation for your retaining wall is crucial  The depth of the trench for the retaining wall should allow for 4-6” of ¾-inch crushed gravel. The crushed gravel helps ensure the right amount of compaction. The earth is pounded using a hand tool for smaller spaces. A tampering rammer is used for larger areas. It compacts the earth and helps level the ground to prepare for the gravel. 

Round rocks and pea gravel can be used for weight to fill hollow blocks. They cannot be used to prepare for a foundation. They move and shift far to easily from the pressure of the weight. Larger retaining walls may require a footing below the frost line. Most jurisdictions, like Halifax Regional Municipality, require that retaining walls higher than 1 metre must be designed by a professional engineer.

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Retaining Wall Construction
Image of small trench being dug as a foundation for a support wall around a property.

Add 2 Layers of Crushed Gravel

After the 4-6″ layer of crushed gravel is added Underground Landscaping compacts and levels it. The finished base for a retaining wall should be so compact that the gravel is not displaced when you walk on it. After the crushed gravel is compacted, another 1” layer of ¼” gravel or coarse sand is added to the top to embed the individual retaining blocks in. 

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Retaining Wall Construction
Image of crushed rock in a trench being used as a foundation for a retaining wall. The grave should be minus 3/4" to provide a solid foundation for the retaining wall blocks.

Lay and Level the First Row of Concrete Blocks

The depth of the first row of blocks can vary depending on the height of the retaining wall and the slope of the ground. Thus, the ideal depth of the retaining wall can vary between between 10 to 40% of its height. The average value is 20% or one-fifth of its height.  below ground level. A good rule of thumb is to construct the first row of blocks 1″ below ground level for each 8″ of height. Nuilding a good foundation is the key to ensuring its stability.

The concrete blocks are placed with each edge touching its neighbour. It is critical that the blocks are level on all sides, both front to back and side to side. You can use a rubber mallet to tap the blocks into place. Add some coarse sand below it if you need to mke sure the retaining wall blocks  are level. A small level can be useful for each block, while placing a 2 x 6” across several can ensure that the whole layer is level.

Retaining Wall Construction
Image of the first row of cinder blocks placed for a retaining wall. After each rowis leveled it should be backfilled for drainage and stability.

Drainpipe and Landscape Fabric?

Retaining Wall Construction

If the wall is constructed properly, with at least one foot of gravel backfill, then retaining walls under one metre do not normally require either a drainpipe or landscape fabric. However, ALL walls built from poured concrete or cinder blocks require additional measures for drainage. Depending on the soil (clay) and/or the slope of the hill, one may want to add a landscape fabric and/or a 4 inch drainpipe for walls under one metre. A landscape filter is useful as a measure to prevent the earth from gradually invading the gravel backfill. A drainage pipe provides even greater protection and is mandatory for retaining walls over over 1 metre (less than 4 ft.).

Retaining Wall Construction
Image of a gravity wall being built for a residence. Such walls provide stability and help properties to drain properly without soil erosion and other damage by storm water.

Add Layers to the Height and Backfill

The layers for the retaining wall should slope backward slightly. It should look as if they lean into the slope of the hill. The stepback slope is referred to as the “batter”.  The incline toward the slope of the hill provides added resistance to the lateral pressure and weight of the soil and earth being retained. The slope should be about 1/2 of an inch for each foot of the  vertical height of the wall. Do not use soil or dirt. Soil retains water, which can create an odor in the summer. Retained water will also freeze, which increases pressure on the wall. Gravel and sand don’t absorb water.

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Cross-section of a Gravity Retaining Wall

Image of a cross-section of a gravity retaing wall. It displays the setback of the wall based on its height, along with recommendations for the backfill for the wall and other items like drain tile.

FAQ

Retaining Walls

A retaining wall is a wall that is constructed in order to provide stability between two stretches of ground that border one another that are different heights. The retaininng wall provides stability for the ground that is higher. Seability ensures that the retaiining wall does not tumble down or get washed down by storm waters to the lower level of ground.

A retaining wall is used when one area of ground is higher than another stretch of ground beside it and the difference in the slope between the two is large. The higher area of ground will gradually spill over to the lower area. 

For example, a building lot might be situated on a hill, and the property owner has to excavate and clear a level lot into the hill. Excavating and landscaping a level lot means the ground will be higher at the back and on each side of the lot compared to the cleared area at the front of the lot. If the lot is big enough, then it is possible for the back and sides to be remade into new small angled slopes for drainage. Then you can use seed to plant grass or flowers, etc. As long as you have the space to slope the ground, you can plant a lawn or used for some form of garden and the grounds will still drain properly. Often the size of the lot does not allow for the space that is required to reshape the slope of the grounds. This will not allow for proper drainage for the property. In such cases, a retaining wall is required in order support and hold back the earth from the higher ground . A retaining wall keeps the higher ground stable so that it does not spill over on to the lower portion. The retaining wall is constructed so that it also provides for good drainage at the point between the two areas of ground.

Retaining walls are crucial for providing support and stability for one area of ground on the lot or property that is higher than an adjacent area of ground.

However, they are also very useful for two other purposes. First, constructing a retaining wall on a property with a steeper slope can reduce the effects of soil erosion and the washing away of earth. Storm waters and spring thaws cam do significant damage to your property.. A retaining wall creates a level area to slow the speed of the water and spreads the storm water out so that it has less force as it drains downward.

Second, constructing a retaining wall into a hill creates a level space for use. Once you make a level space, you can plant flower or rock beds to enhance the appearance of your home or property. You could also add a patio area for relaxing or even a place for a barbeque and/or a firepit.   

Wood, stones or rocks, bricks, poured concrete, and concrete or cinder blocks are the common materials used to construct a retaining wall. Concrete or cinder retaining wall blocks have become very popular because they can interlock with each other for extra security and are heavy enough to remain stationary without the use of cement or some other adhesive.

Hollow concrete and cinder blocks are readily available and a popular choice. They are lighter to use and can be filled with rocks in order to provide greater weight.

Concrete blocks for a retaining wall are composed from steel, cement and wood. The sand and stone to used for the cement make them heavy. Cinder blocks are made from concrete and coal cinders.  

A gravity retaining wall refers to a wall that is based solely on the mass of the material of the wall. The wall itself provides enough weight to resist the forces of gravity from the soil and earth that it is retaining so that the wall does not fail. It is the most widely used for lower heights because it is the easiest to construct. 

Poured concrete is the strongest type of retaining wall by far. The higher the wall, the more likely that poured concrete will be used. The downside tp poured concrete is that it requires a lot of preparation and is more expensive. Cracks are also possible if the concrete is not mixed and poured properly.