But if you have a solid retaining wall, such as a concrete basement wall, provisions must be made to drain away the water (or it might collect behind the wall and cause cracking). Stackable retaining block walls with gravel or sand backfills don’t typically have drainage issues, since water seeps down through the backfill and drains out between the individual blocks. This decreases the risk of cracks and damage. Meanwhile, gravel and sand don’t swell or retain water, so the wall will be subjected to less pressure. Dirt absorbs water and swells when saturated, which will put unwanted pressure on the back of the wall. The space directly behind a newly constructed retaining wall should be filled with gravel or sand-not dirt. Since frost levels vary from one region to the next, contact your local building authority to determine the details before building a large retaining wall. Footings poured too shallow are prone to shifting and moving if moisture in the soil freezes and heaves. To create this, a landscaper pours concrete below frost level (the depth to which the ground will freeze during the winter). A buried structural footing is usually required for larger retaining walls. FoundationĪ trench filled with gravel provides a suitable foundation base for a short, step-back retaining wall with three-five courses (each layer of blocks is called a “course”). This type of wall isn’t common, however, because it requires an extensive amount of stone or concrete for construction. Depending on the height of the wall and the pressure of the earth behind it, the extra supports could be in the form of buried footings, steel reinforcement, cantilevered design, or tie-backs that extend deep into the earth behind the wall and connect to buried anchors called “dead men.” You could also add extra strength with a “gravity wall,” which is so wide that its weight serves as a buttress against the pressure of the soil behind it. This includes vertical walls that don’t slope toward the contained earth, as well as walls higher than three feet. Some types of retaining walls require additional structural support to keep them from toppling over. Step-back walls can be built by anyone with a strong back and basic construction knowledge, as long as they have blocks designed for retaining wall assembly. This design, known as “step-back construction,” creates a sturdy wall structure that pushes back against the lateral pressure of the soil behind it. When building a retaining wall, landscapers often slope them slightly toward the earth they’re containing. You’ll also want to call DigSafe (811) to have representatives from local utility companies come out and check whether any buried electrical lines will be in the way. Local building codes and ordinances vary between communities, so don’t skip this step. Retaining walls can alter water flow and affect your neighbors, so you may need to obtain either a zoning permit or a building permit. If you’re planning to build a retaining wall, check with your local building authority beforehand. The contractor may also charge more for labor and materials if he has to pour a deep frost footing (explained below) or remove tree roots that are in the way of the footing. A natural stone or brick retaining wall laid by a mason can cost upwards of $20 per square foot, and a poured concrete retaining wall will set you back $13 to $18 per square foot. A small retaining wall less than three feet in height will cost an average of $5 to $8 per square foot, if you build it yourself. Larger retaining walls, which are not DIY-friendly, are pricier due to the labor costs involved. These blocks cost between $1.25 and $4 per block, depending on their size and texture, and they feature locking flanges that attach each row of blocks together. But, if you’re looking to undertake a do-it-yourself job, retaining wall blocks (available at most home improvement stores) are your best bet. Retaining walls are often constructed with concrete, stone, or bricks. You’ll also find retaining walls in parks and public gardens, where they act as retainers for plants, statues, and decorative landscaping elements. They’re indispensable in the creation of sunken patios, walkout basements, and any other hardscape with an abrupt separation of ground elevation. Retaining walls have a wide variety of uses around the yard, all of which involve keeping earth from spilling off a steep slope.
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