Denver Retaining Walls

A retaining wall is two structures. There's the one you can see, which is concrete and looks like the whole job. And there's the one behind it, made of rock, fabric, pipe, and compacted fill, which is what decides whether the visible half is still straight in fifteen years.

We build engineered concrete walls all over Denver. Terraced back yards in the Highlands and around Sloan's Lake, grade changes on Park Hill lots where the garage sits lower than the house, driveway and patio walls in Cherry Creek. What we spend the most time on is the part that gets buried on the last day, because that's the part that has to hold.

Wet soil weighs a lot more than dry soil

Here's the mechanism, plainly. Soil behind a wall pushes sideways. How hard depends on how tall the pile is, how steep it runs above the wall, and above all whether that soil is holding water. Saturate the backfill and you add the full pressure of standing water to everything the soil was already doing. That's why walls tip out, crack along a horizontal line, or slide off their footings in a wet spring and not in a dry August.

So a drained wall carries a far smaller load than an undrained one of the same height. Everything behind the concrete exists to keep that soil from becoming a reservoir. Rock against the wall so water falls instead of pooling. Fabric so silt doesn't clog the rock. A perforated pipe at the bottom with real fall on it. Weeps through the face for anything that gets past all of that. And a cap of tighter soil up top so runoff sheds instead of soaking in.

What goes behind the wall

The footing, the batter, and the height that changes everything

Under the wall, bearing rules. The footing has to sit below frost and on material the engineer accepts, which on some lots means digging past whatever fill a previous owner used to level the yard. A footing bearing on old fill is a wall with an expiration date. We check the bottom of the trench rather than assuming the plan got it right.

Above ground, we build most walls with a slight lean back into the hill. Batter buys margin: if the wall moves a fraction over the decades, it moves toward plumb instead of past it. Height is the other threshold. Short garden walls are landscape work. Once a wall gets tall enough to matter, or has a driveway, patio, or slope loading it from above, it's a structural element with a stamped design behind it. Our engineer draws those in house.

Every leaning wall I get called out to, I dig one hole behind it and find clay packed right up against the concrete. Every time. The wall was never the problem.Our crew lead, after the walkthrough

What we build behind the concrete

• Footing trench taken to bearing the engineer signs off on, below frost depth
• Steel tied continuous through the footing and up into the stem, lapped to the drawing
• Damproofing on the retained face before any rock goes in
• Washed rock chimney against the wall, wrapped in filter fabric top and bottom
• Perforated drain at the base with measured fall to daylight or a collection point
• Backfill placed in lifts and compacted, never dumped from a bucket in one go
• Machine kept back off the wall so track loads don't push it while it's green

When to build, and what a Denver winter does to a wall

Spring through fall is the window, and early fall is the best of it. The ground is dry, the excavation stands open, and backfill goes in at a moisture that actually compacts. We'll pour walls into the cold with warm mix water, accelerator, and blankets, and we won't place on frozen bearing. But the real winter problem isn't the concrete. It's the dirt. Frozen clumps bridge instead of compacting, then thaw into voids that show up in April as a sunken patio behind an otherwise fine wall.

Winter also runs the freeze thaw test on everything you built. Water trapped behind a wall expands as it freezes and pushes, night after night. That's why a wall that seemed fine in October looks different in March. If yours moved over a winter, the drainage behind it is telling you something.