When Does A Slope Need A Retaining Wall?

large gray retaining wall in autumn backyard with red trees and green grass

If you are staring at your sloping yard and wondering whether you need a retaining wall, this article is for you.  It can be difficult at first to determine whether or not you need a retaining wall.  What if you don’t install a retaining wall, what are your other options?  Ultimately, when does a slope need a retaining wall?

Retaining Wall Planting Considerations

First, the question to ask is what is planted. Furthermore, what do you want to plant on the slope? It’s perfectly fine if you don’t want to plant anything. Will you be planting grass or will it be a planting bed?  You can get away with a slightly greater slope with a planting bed than you can with a lawn.  Yes, you can plant grass on a steep slope, but you might open yourself up to some erosion issues and just plain unsafe mowing conditions if you do.  

When Does A Slope Need A Retaining Wall?

The rule of thumb for a lawn’s maximum slope is 4:1.  This means for every 4 feet, your grade elevation can change by up to 1 foot.  For a planting bed, the rule is 3:1.  If you aren’t planting the slope at all, and will instead be using rip rap (large crushed rock on the slope) you can have a 2:1 slope. Obviously a rip rap slope is not the most beautiful thing to look at unless you are getting creative.  Most of the time you see rip rap it’s used on the edge of roadways, or along stream beds to prevent erosion. To answer the original question, you need a retaining wall when the slope exceeds 2:1

Lawn Slope

lawn slope backyard with green trees spread out in front of a brick wall

Planting Bed Slope

driveway showing green, red and white plants sloping over a rock wall

Rip Rap Slope

rip rap slope with gray granite steps leading down to the backyard of a beach home

How And When To Install A Retaining Wall On A Slope

If none of these solutions will work in your sloping yard, you will need to consider a retaining wall. You can install a retaining wall in numerous ways.  You can terrace the yard with multiple low retaining walls.  Alternatively, you can cut into the slope and build one large retaining wall.  Whatever you do, make sure you prepare the retaining wall construction area properly, get the appropriate engineering, and have the work completed by an experienced contractor who you know by reputation to stand behind their work.

Terraced Retaining Walls 

terraced retaining wall made of brown corten steel in an upscale backyard with green flowers and a fountain

Single Large Retaining Wall

large block retaining wall with green shrubs emerging from distant view of the wall with green grass below and brown mulch above

When Does A Slope Need A Retaining Wall Summary

So when does a slope need a retaining wall?  You need a retaining wall when the slope exceeds 2:1.  You may want a retaining wall in any case for aesthetic reasons or to make an area slope in the opposite direction.  In the end there are multiple reasons to build a retaining wall, and so long as you do it right, it’ll be there for decades.