Q: What's the difference between a retaining wall, a planter wall, and a CMU block wall?

A retaining wall is a structural wall built to hold back soil on a slope or grade change — it's load-bearing and engineered to resist ongoing soil pressure. A planter wall is shorter and decorative, used to define garden beds or raised planting areas; it holds soil but isn't typically load-bearing in the same way. A CMU block wall is built from concrete masonry units and is generally used for property division, privacy, or perimeter walls rather than holding back soil — it's a structural wall serving a different purpose than a retaining or planter wall.

Question 1

What's the difference between a retaining wall, a planter wall, and a CMU block wall?

Accepted Answer

A retaining wall is a structural wall built to hold back soil on a slope or grade change — it's load-bearing and engineered to resist ongoing soil pressure.

A planter wall is shorter and decorative, used to define garden beds or raised planting areas; it holds soil but isn't typically load-bearing in the same way.

A CMU block wall is built from concrete masonry units and is generally used for property division, privacy, or perimeter walls rather than holding back soil — it's a structural wall serving a different purpose than a retaining or planter wall.

Question 2

Do retaining walls need drainage if Arizona is so dry?

Accepted Answer

Yes — even in a dry climate, drainage is essential. Arizona's monsoon storms create short, intense bursts of runoff, and without proper drainage (weep holes, gravel backfill, and drain piping behind the wall), water pressure builds up quickly behind the wall and can lead to bulging, cracking, or eventual failure.

The dry stretches between storms don't reduce the need for drainage — the intensity of the storms when they do hit is what makes it necessary.

These issues are typically caused by inadequate base preparation, poor compaction during installation, or missing/undersized drainage — all things a licensed contractor accounts for from the start.

Question 3

What wall needs waterproofing?

Accepted Answer

Planter walls need waterproofing — since they hold soil and moisture directly against the wall on an ongoing basis (especially with irrigation or drip systems running behind them), they're the most exposed to water intrusion of the three wall types.

Retaining walls typically rely more on backfill drainage (gravel, drain pipe) to move water away rather than a membrane, and CMU block walls generally aren't holding soil against them at all, so waterproofing isn't usually necessary there.

For planter walls, the waterproofing membrane or water barrier fabric should be applied on the soil-facing side of the wall, starting at the base/footing and running up to at least the soil grade line — ideally a few inches above where the soil sits, so water can't wick up and over the top of the barrier. This protects the finished face of the wall from moisture migrating through the block or stone, which is what causes efflorescence and long-term structural weakening.

Retaining Walls, Planter Walls & CMU Block Walls

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Retaining Wall, Planter Wall & CMU Block Wall FAQs

Answers to the most common questions homeowners ask about walls in Arizona

What's the difference between a retaining wall, a planter wall, and a CMU block wall?

Do retaining walls need drainage if Arizona is so dry?

What wall needs waterproofing?

Get An Estimate

Retaining Walls, Planter Walls & CMU Block Walls

Built to Hold, Built to Last

Retaining Wall, Planter Wall & CMU Block Wall FAQs

Answers to the most common questions homeowners ask about walls in Arizona

Question

What's the difference between a retaining wall, a planter wall, and a CMU block wall?

Question

Do retaining walls need drainage if Arizona is so dry?

Question

What wall needs waterproofing?

Get An Estimate