Los Angeles is a city built on slopes, and most of those slopes are held back by something. A retaining wall is not decorative masonry — it is a structure resisting a load that never stops pushing, and the walls that fail here almost never fail because the blocks were wrong. They fail because water got behind them and stayed there. This guide covers the block types we stock, what each one is honestly good for, and the footing, drainage and backfill details that decide whether a wall lasts thirty years or one wet winter.
Height is the first question, and it is a permit question
Before choosing a block, find out how tall the wall has to be, because height determines whether this is a weekend project or an engineered one. Low garden and planter walls are generally treated as landscape work. Above a certain height — and the threshold, how it is measured, and whether the wall carries a surcharge from a slope, driveway or structure above all vary by jurisdiction — a retaining wall requires a permit and a design stamped by an engineer.
In Los Angeles the surcharge part matters more than people expect. A four-foot wall at the bottom of a steep canyon slope is carrying far more than a four-foot wall in a flat backyard, because the soil behind it keeps rising. Anything holding back a slope above a house, a driveway, or a neighbour's property is an engineering question, not a product question. Ask your local building department where the line sits before you order material.
Everything below assumes a modest, non-surcharged residential wall. Scale up and the rules change.
Block types and what each is really for
Retaining blocks divide into three practical families, and the difference between them is how they resist the soil: by weight and friction, by mechanical setback, or by steel and grout.
| Wall Type |
Best For |
Needs |
Watch For |
| Dry-stack block |
Low garden walls |
Compacted base |
Height limits apply |
| Setback lip block |
Terraces and planters |
Level first course |
Backfill and drainage |
| Mortared CMU |
Taller walls |
Footing and rebar |
Permit and design |
| Timber or tie |
Rustic low walls |
Deadmen anchors |
Wood in soil contact |
The setback column is the one worth understanding. Dry-stack landscape blocks lean the wall back into the hill a fraction of an inch per course, and that lean is what keeps the wall in compression instead of tipping. The 6-3/4 in. x 4 in. x 11-3/4 in. beige wall block has a self-aligning rear lip that produces the setback automatically, which is why it forgives an imperfect hand more than a flat-faced block does. Interlocking units like the 10 in. x 6 in. x 16 in. tan wall block dry-stack to about three feet without a poured footing, which covers a large share of residential terracing. Smaller units such as the 6 in. x 3 in. x 10 in. Sierra blend block top out lower — around two feet including the buried first course — and belong in planters, tree rings and bed edging rather than in anything structural.
When the wall has to go taller or carry load, it becomes reinforced masonry. The 8 x 8 x 16 in. gray bond beam block is the unit for that: its knock-out webs let horizontal rebar run continuously through the wall so the whole assembly can be grouted solid and tied to vertical steel from the footing. That is a different build with a different inspection, and it belongs to whoever stamped the drawings. Browse the full range in our blocks collection and the wider masonry collection.
The base course decides the wall
Every hour spent on the first course pays back and every shortcut compounds. Excavate below grade, compact the subgrade, and set the first course in a levelled bed of compacted crushed base — then bury it. A buried first course resists the wall sliding forward at the bottom, which is the failure mode nobody plans for.
Level matters in both directions. A first course that is out of level side to side telegraphs the error upward and grows with every row, and a course that is out of level front to back throws away the setback the block was designed to give you. Check it with a long level, not a short one, and reset rather than shim.
For mortared masonry the base is a poured concrete footing sized and reinforced per the design, with vertical steel left protruding to tie into the wall. Our guide to rebar accessories covers the chairs and ties that hold that steel where the drawings put it, and our mortar types guide explains why Type S is the LA default for structural masonry — our pre-blended Type S mortar is what most of these walls are laid with.
Drainage: the part that actually fails
Saturated soil weighs far more than dry soil and it pushes with hydrostatic pressure a dry backfill never generates. A wall designed for dry conditions and then asked to hold back a bathtub will move, and in Southern California it moves in a single storm after years of looking fine.
The fix is a drainage chimney behind the wall. Backfill the zone directly behind the block with clean, free-draining aggregate rather than the native clay you excavated — 3/4 in. gravel is the standard choice and it is sold by the bag for small walls. At the base of that gravel, lay a perforated collector pipe running to daylight or to an approved drainage point; the 6 in. perforated S&D pipe is what we stock for it, and it needs continuous fall along its length, not a level trench.
Separate the gravel from the soil with filter fabric, wrapped so fines cannot migrate in and clog the aggregate. A woven landscape fabric does the job. Without that separation the chimney silts up over a few years and quietly stops working, which is why so many failed walls look fine from the front right up until they do not.
Weep holes through the face of a mortared wall are the other half of the system. They are not optional decoration; they are the exit.
Backfill and compaction
Backfill in lifts, compacting each one, and keep the compactor off the block itself — over-compacting directly behind a segmental wall pushes the courses forward. Six to eight inch lifts are the usual working rhythm.
Do not use the excavated hillside clay as backfill in the drainage zone. Clay holds water, swells, and applies exactly the pressure the design is trying to avoid. Native soil above and behind the aggregate chimney is normally fine; native soil against the block is not.
Finish by grading the surface behind the wall so surface water runs away from it rather than into it, and make sure downspouts and hardscape are not discharging onto the backfill. On a bare slope above a new wall, the measures in our hillside erosion control guide keep soil and water off the structure while planting establishes; below it, the drainage and paving choices in our concrete pavers guide decide whether runoff spreads or channels.
Timber walls and terracing
Wood retaining walls remain common on LA hillsides, and they are legitimate for low, rustic work when built with deadmen tied back into the slope and with the same drainage stack behind them. The material rule is simple: anything in soil contact must be rated for it — see our note on pressure-treated lumber. Untreated timber in wet backfill is a decade at best, and the failure is sudden.
The better answer on a steep yard is often not one tall wall but two short ones. Terracing splits the retained height, keeps each wall inside the range where a dry-stack or setback block system works without engineering, and creates usable flat ground between them. It is more block and more digging, and it is usually the cheaper wall in the end.
Ordering for the job
Blocks are heavy, and delivery rather than availability is what drives the schedule — our note on concrete block pallet counts and delivery covers how the material actually arrives on an LA street. Calculate face area rather than linear feet, add the buried first course, and add breakage on any wall with cuts or curves.
Order the drainage materials at the same time as the block. The gravel, the pipe and the fabric are what people run out of on day two, and a wall that gets backfilled with whatever is on site because the aggregate did not arrive is a wall with a problem built into it. We deliver block, aggregate, mortar and drainage material across Los Angeles County — send us the wall height and length and we will build the list.
Frequently asked questions
How tall can I build a retaining wall without a permit?
It depends on your jurisdiction and on whether the wall carries a surcharge from a slope or structure above. There is a common threshold around four feet measured from the bottom of the footing, but it varies and surcharged walls are often treated differently. Confirm with your local building department before you order.
Do dry-stack landscape blocks need a footing?
Not a poured concrete footing at typical landscape heights, but they absolutely need a compacted, levelled base course set below grade. The base is doing the footing's job; skipping it is what produces the leaning garden walls you see all over the city.
What gravel goes behind a retaining wall?
Clean, angular, free-draining aggregate — 3/4 in. gravel is the usual choice. It should be clean rather than a fines-rich crushed base, because the point is for water to move through it freely to the collector pipe.
Do I need a drain pipe behind a low wall?
On a short, free-draining planter wall in sandy soil you may get away without one. On any wall retaining a slope, in clay soil, or where water collects, a perforated pipe daylighting to a safe discharge point is the difference between a wall and a future repair.
Can I use regular concrete block for a retaining wall?
Only as engineered, reinforced masonry — grouted solid with vertical and horizontal steel on a designed footing. Standard CMU dry-stacked or laid without reinforcement is not a retaining wall, whatever it looks like when it is finished.
What happens if I backfill with the soil I dug out?
On a hillside lot that soil is usually clay-heavy. It holds water, swells when wet, and loads the wall with pressure the design never assumed. Use free-draining aggregate in the zone behind the block and save the native soil for above and behind it.
