Retaining Wall Construction in San Carlos, CA

Retaining wall construction

The wall you see is holding back a lot of weight

What goes under a retaining wall?

A leveling pad. We dig a trench along the line of the wall, take out the loose and organic material, and put down compacted crushed stone, level and wide enough that the block sits fully on it with room either side. Get that pad right and the whole wall is right, because every course above copies it. It is the same trench and pad start behind all of our block and stone work.

The first course is buried, normally about one course of block for every eight courses of height, and more at the bottom of a slope. That buried course is what stops the base of the wall from being pushed out, and it is the single most common thing missing from a wall that has started to lean.

We set it by hand with a level on every block, then check the string end to end before anything goes on top. It is the same fussy base work that goes under every paver surface we install.

What is batter, and when does a wall need geogrid?

Batter is the lean. Each course is set back slightly from the one below, so the wall tips into the hill rather than standing dead vertical. It looks like a detail and it is not: that lean puts the weight of the wall against the soil it is holding, and on a steep Belmont lot it gives you a margin before any small movement ever reads as a wall leaning out.

Geogrid is the other half. It is a stiff mesh laid between courses and running back into the backfill, so several feet of soil behind the wall become part of the structure. Short garden walls often do not need it. Anything tall, anything with a slope continuing above it, and anything with a driveway or a pool near the top needs it designed rather than guessed, and in California a wall over four feet, or any wall carrying a surcharge like that, is engineer and permit territory.

Allan Block publishes the engineering this system is built on, and we are certified to install to it.

Why does the drainage behind the wall matter more than the block?

Because water is what actually knocks walls over. Wet clay behind a wall is far heavier than dry soil, and trapped water adds pressure of its own on top of that weight. Our winters do not rain evenly, they rain hard for a week, and that is exactly the condition a poorly drained wall fails in. It is the same water we chase off the paving with trench drains and catch basins lower down the property.

So behind every wall we build a drainage zone: clean angular stone filling the space directly behind the block, a filter fabric separating that stone from the soil so fines never wash in and plug it, and a perforated drain pipe sitting at the bottom of the stone with a fall on it and a real outlet at the end. A wall with a pipe that ends nowhere is a wall with no drainage.

Where a flight cuts through the wall, the same stone and pipe carry on behind the steps themselves, so the whole slope drains as one system.

Why choose Exterior Designs for your retaining wall?

Hillside work is most of what we do. Belmont and Hillsborough lots are steep, a lot of the soil out here is clay that moves with the seasons, and the wall is usually only one part of a job that also involves a drive, a patio, steps and where the water goes. Having one company plan all of it means the levels, the drainage and the finish actually line up.

We are an Allan Block Certified Installer and an ICPI Certified Paver Installer, family owned and operated, working only in interlocking pavers and natural stone. Every installation carries a 20 year warranty and estimates are free. If a bank is slipping, a wall is leaning, or you want a flat piece of yard you do not currently have, ask for a free estimate on the slope and Todd will come and look at it himself.

How tall can a retaining wall be without an engineer?

As a rule of thumb, walls over four feet measured from the bottom of the footing need engineering and a permit in California. So does any shorter wall carrying a load near the top, such as a driveway, a pool or a continuing slope.

Why is my existing wall leaning forward?

Nearly always no buried first course, no drainage behind it, or no reinforcement into the soil on a wall tall enough to need it. Leaning is the soil winning. It does not correct itself, and the repair is a rebuild.

What is the difference between block and a stone faced wall?

Segmental block is the structure and does the holding. A stone face is a veneer set on the front of that structure when you want natural stone. Both use the same pad and drainage behind them, so the choice is appearance, not strength.

Can you build a wall against the property line?

Often yes, but it has to be planned. We need room to excavate behind the block for the drainage zone and, on a taller wall, room for the grid to run back into the soil. Tight access sometimes moves the wall forward slightly.

Will plants or trees damage the wall?

Large tree roots directly behind a wall can over years, so we look at what is growing on the bank first. Planting on top is usually fine, though irrigation up there needs control, since a leaking line saturating the backfill acts like a drainage failure.

Do you build retaining walls outside San Carlos?

Yes, and most of ours are outside it. Hillsborough, Belmont, San Mateo, Burlingame, Redwood City, Menlo Park and Atherton are all inside our normal working area on the Peninsula, and the estimate is free wherever the job is.