Proper Drainage Behind Retaining Walls: What Most Builders Skip
Proper Drainage Behind Retaining Walls: What Most Builders Skip
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A Wall’s Real Enemy Isn’t Gravity — It’s Water
One of the biggest reasons retaining walls lean, crack, or collapse is simple: water. It builds up behind the wall and creates pressure that pushes outward. Most failures happen because this pressure isn’t accounted for — or the drainage system was never installed at all. Here’s how we do it right, every time.
What Happens Without Drainage
What Happens Without Drainage
Water trapped behind a wall has nowhere to go. Over time, it saturates the soil, increases weight, and freezes during cold months. This expansion pushes the wall outward, often slowly at first — until one day, it shifts visibly or fails completely.
Drainage Starts With the Right Backfill Material
Drainage Starts With the Right Backfill Material
We never backfill walls with dirt or clay. Instead, we use:
A minimum of 12 inches of clean 3/4-inch crushed gravel
Filter fabric to separate gravel from native soil
Compacted in lifts to prevent future settling
This setup prevents water from being trapped and reduces hydrostatic pressure.
Perforated Drain Pipe Placement
Perforated Drain Pipe Placement
Every structural wall includes a perforated drain pipe — also known as a French drain — placed at the bottom of the gravel zone behind the wall.
The pipe is sloped to daylight or a gravel drywell
It is sock-wrapped if soil fines are a concern
Covered with clean gravel to maintain flow
Weep Holes Are Not Enough
Weep Holes Are Not Enough
Some builders drill small weep holes into the face of the wall, but this is not a true drainage system. These often clog and fail to relieve enough pressure. A proper drainage system is placed behind the wall, not just in front.
When Extra Drainage Is Needed
When Extra Drainage Is Needed
For tall walls, poorly draining soils, or slopes above the wall, we may add:
Double-layered pipe systems
Vertical gravel columns
Surface swales or regrading above the wall
How to Know If Your Wall Was Built Right
How to Know If Your Wall Was Built Right
Look for the following:
Visible gravel behind or above the wall
An open drain pipe discharge
No bulging, cracking, or leaning
A dry base at the wall toe even after rain
If these are missing, you may have a drainage issue waiting to happen.
Related Services:
Related Services:
Need to Retrofit or Rebuild a Wall?
Need to Retrofit or Rebuild a Wall?
If your wall is already leaning or you're planning a new one, we’ll help you get it right. Drainage is one of the most important — and invisible — parts of your landscape.
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