How To Build A Retaining Wall On A Slope Guide

sloping backyard with a few small retaining walls installed

When your backyard drops off or slopes up drastically from your back door, it can be frustrating to try and play a simple game of catch.  The backyard needs to be leveled out, but what’s the best way to do it?  If you have a slight slope, you can either scrap material away or fill in to flatten the yard, adding a steeper sloping area at the transition.  But when the slope is too great to overcome with grading you need retaining walls.  You may find yourself asking how to build a retaining wall on a slope.  

How To Build A Retaining Wall On A Slope

Over the past 20 years, we’ve had many homeowner’s projects that involved retaining walls. After all, having a perfectly leveled backyard to start is very uncommon. Luckily, this doesn’t mean that your backyard is doomed. With a little creativity, sloping backyards can be even more beautiful and have more design options than a flat yard. In this article, we’ll explain the process of how to build a retaining wall on a slope.

how to build a retaining wall on a slope guide

Step 1: Soil Samples And Professional Help

First you need to get professional help.  The type and amount of help depends on many factors, one being the retaining wall height. Other considerations are your soil types and the region of the world you live in. You probably want to have a team of engineers dictate how to build the retaining wall. 

First you need to know your soil conditions, as this is the way all structural engineers begin their calculations.  If you don’t provide them with soil conditions they will make an assumption based on your location.  Soil sampling is provided by geotechnical engineers who will either drill borings before any work begins, or inspect the open hole at excavation and provide a report to the structural engineer.  

Once you have the bearing capacity of the soil understood, your structural engineer can provide their wall design.  You will need to choose the type of retaining wall you want to build and who you want to build it.

Step 2: Retaining Wall Footing Excavation

The next step is to excavate for the retaining wall footing.  At this point the excavation will usually remove a large amount of soil behind the wall in addition to the soil removed for the footing.  This is for a couple of reasons.  One being excavation safety which requires benching of the excavation depending on soil types to prevent soil wall collapse during construction.  The other reason you want to over excavate behind the wall is to provide engineered well draining fill to prevent water and frost damage to the wall after completion.  This will be designed and specified by your structural engineer.  

Step 3: Retaining Wall Footing Installation

Since you are building on a slope and the footing is installed flat, the footing depth will be calculated from the downhill side of the slope.  Once the footing excavation is complete, it is time to install the footing.  This will usually consist of a poured concrete footing which in cold climates will be set below the frost line, 3’ to 7’ below grade depending on your location.  With some precast block systems in particular, you can use the first course of block as your footing. Therefore, you don’t need to pour a footing.

Step 4: Retaining Wall Construction

Once you have your footing placed, it’s time to begin the wall itself.  Depending on the type of wall it’ll be either a precast block system, poured concrete, masonry, or a combination.  With precast block walls, as you build the wall you will want to backfill the wall with engineered fill, usually crushed, washed stone.  With poured concrete walls, you will pour the wall, remove the form work then backfill the wall all at once.  

The engineer will provide details related to the grading at the top of the wall.  Usually they want the grade to slope down and away from the top of the wall for a certain distance, often 3’ or so.  This prevents surface water buildup against the wall when the ground is frozen. It also prevents surface water from flowing to the wall itself.

Extra Ideas For How To Build A Retaining Wall On A Slope

Once you have your wall complete and backfilled, it’s important to consider how you will prevent people from walking over the edge.  Do you want to install a railing at the top of the wall?  Do you want to landscape the area behind the wall to keep people from walking to the edge?  Whatever you do, it’s a design consideration you cannot ignore as a homeowner.  The safety of your backyard should always come first regardless of how to build a retaining wall on a slope.