I just dated myself with that title. Yes, I know it’s also pretty lame.
Usually perceived as a way to skirt regulations or cut costs, homeowners and contractors alike will turn to terracing as the solution for holding back large or steep slopes.
The Law of the Land
Let’s start with regulations. Any wall over 4 feet in height needs a stamped engineered drawing and a permit. I can’t speak for other states, but this holds true in Pennsylvania. I’ve seen walls that are 3-ish feet tall and immediately behind that wall will sit another wall about 2-ish feet tall. Math is math though. We still have 5 feet total height of heavy concrete block holding back the slope. Beyond violating building code, this is a dangerous situation. The bottom wall has to hold up the slope AND the weight of the upper wall. Something has to (and will) give.
In the above example, I’m assuming that neither of these walls was reinforced with geogrid (another topic for another blog post). Reinforcement is the only way that a terraced situation like that will stand the test of time. ‘Like that’ meaning the two walls are close together.
There is one other way to create terraced walls without reinforcement. You just have to have the space to make it happen. A good rule of thumb for spacing terraced walls sans geogrid reinforcement is this: take the height of the lower wall, multiply it by 2 and that is the number of feet that you must have between the upper wall and lower wall. This ensures that the upper wall is not adding extra force to the wall below. In the above example, if the bottom wall is 3 feet tall, then you would need to excavate back at least 6 feet into the slope before starting the upper wall.
Let’s Talk Dollars
On to the cost of terracing. Whether you reinforce both walls or use the handy rule of thumb from above, terracing generally costs more than creating a single taller wall. Even with good distance between the walls, there is a lot of dirt to be excavated. It also adds more linear feet of base course. The most time consuming portion of the wall is prepping base material and leveling the first course of block. Terracing takes double the time.
It’s Not All Negative
Terracing is a great way to add some visual interest to a slope. The space between the walls allows for some plantings to soften the landscape. It can also be a great way to open up a space that otherwise might feel closed off (think tall wall in a confined space). I don’t want you to think that I’m against terracing. I just want you to be in the know about the right way to do it!