Retaining walls rarely fail suddenly. There are almost always warning signs — sometimes subtle, sometimes obvious — that appear weeks, months, or years before a complete failure. The problem is that most homeowners don't know what those warning signs look like, so they miss them until the situation is urgent.
Here are the seven things we look for when assessing retaining walls across Burnaby. If you see any of these on your property, it's time to get the wall looked at — not next spring, not when you get around to it. Before the next rainy season.
1. The Wall Is Leaning or Tilting Forward
This is the most obvious sign and the most urgent. A retaining wall that is leaning forward — toward the downhill side — has already moved beyond its designed position. It's experiencing more lateral force than it can comfortably resist.
A small lean — less than 25mm out of plumb over 1.0m of height — might indicate historical settlement that has stabilized. Get it measured and monitored, but it may not be immediately urgent.
A significant lean — 50mm or more out of plumb — or a wall that you can tell has leaned noticeably compared to last season is a wall that's actively failing. This needs professional assessment immediately. If the wall is also showing cracks at mid-height or displacement at the base, consider it an emergency.
2. Cracks in the Wall Face
Not all cracks are equal. Horizontal cracks at or near mid-height of a concrete block or poured concrete wall are a serious sign — they indicate the wall is bending under lateral earth pressure. This is the structural failure pattern for cantilever and gravity walls, and it's telling you the wall is close to its limit.
Vertical cracks are typically less structurally significant — they often indicate differential settlement (one section settling more than another) or thermal movement. They should still be monitored.
Stair-step cracks in mortared block walls (following the mortar joints in a diagonal or stair-step pattern) can indicate either thermal movement or differential settlement. The location and orientation of the cracks matters — cracks concentrated at one end of a wall suggest that end is settling more.
Crumbling or spalling on the surface of concrete block is typically a freeze-thaw issue — low-quality block that isn't adequately air-entrained degrades at the surface over time. This is primarily aesthetic unless it's exposing the interior of the block, but it should be addressed before it worsens.
3. Bulging in the Middle of the Wall
A wall that bulges outward at mid-height — not from the top or bottom but in the middle of the face — is showing the deformation pattern that happens when the wall is bending. The soil pressure is too high for the wall's structural capacity, and the wall face is bending forward at its weakest point.
This pattern is common in concrete block walls that have inadequate or absent reinforcement, and in older brick retaining walls. If you see a noticeable bulge in the face of a wall, get it assessed — this is a pre-failure condition.
4. Water Coming Through the Wall Face
Weep holes should flow during or immediately after rain, then stop. That's normal — that's what they're supposed to do. Water seeping through the wall face between rain events, or at locations other than the weep holes, is abnormal and indicates a drainage system problem.
If water is finding its way through mortar joints, through cracks, or through the face of block between weep holes, it means the drainage behind the wall is saturated or absent. The water is finding its way out through whatever paths are available in the wall face.
This situation gets worse when the temperature drops below 0°C — water in wall cavities and mortar joints freezes and expands, widening cracks and accelerating deterioration. In Burnaby, this freeze-thaw damage primarily occurs during cold snaps in December and January.
White staining on the face of a concrete block or stone wall (called efflorescence) indicates dissolved minerals being carried to the surface by water moving through the wall. It's ugly but not immediately structural — however, it confirms that water is moving through the wall, which is a drainage concern.
5. The Base of the Wall is Displacing
The base course of a retaining wall is the most heavily loaded course — it carries both the weight of the wall above it and the full lateral earth pressure from the bottom of the retained soil. If the base course is tilting, shifting, or being pushed outward, the wall's structural integrity is fundamentally compromised.
Look for gaps between the base course and the adjacent hardscape (patio, driveway, or lawn), a tilted first course, or erosion at the toe of the wall exposing the footing. Any of these conditions warrant urgent assessment.
6. The Drainage Outlet is Blocked or Missing
Every properly built retaining wall should have a visible drainage outlet somewhere — a pipe daylighting at the wall face at low points, weep holes through the block at the base, or a surface outlet at the end of the wall.
If you can't find the drainage outlet for your wall, or if the weep holes are blocked with sediment and vegetation, the wall is likely not draining properly. This is a slow-building problem that gets worse every winter and eventually manifests as hydrostatic pressure damage.
After the next heavy rain event, look at the wall face. Are the weep holes flowing? Is there water coming out of the face? How long after the rain stops does any seepage continue? These observations tell you a lot about the drainage system condition.
7. Soft or Rotted Timber on Timber Walls
Timber retaining walls show their age at the ground line first — where the timber transitions from below-grade soil contact to above-grade air exposure. This repeated wet-dry cycling accelerates decay faster than either fully submerged or fully exposed conditions.
Test timber walls by pressing on the face planks and posts at and just above the ground line. Timber in good condition is firm and solid. Timber that's degrading feels soft, spongy, or crumbles under pressure. You can also probe with a thin screwdriver — the blade should not penetrate easily into sound timber.
A timber wall with significantly degraded posts is not repairable in any meaningful structural sense. The posts are what's holding everything back — when they're soft, the wall's useful life is effectively over. Plan for replacement.
Published by
Burnaby Retaining Wall Experts TeamRetaining wall contractors serving Burnaby and the Lower Mainland