Hillside lots are part of what makes the Peninsula beautiful. Homes in Hillsborough, Belmont, Burlingame, San Mateo and the hills above Redwood City and Los Altos often enjoy views, privacy and mature trees that flat lots simply do not have. But a slope also means less usable yard, and on many properties the retaining walls decide how much of the landscape you can actually live in.

Whether you are replacing an old railroad-tie wall or planning a full terraced backyard, here is what Peninsula homeowners should know before building a retaining wall.

Start with how you want to use the yard

The best retaining wall projects begin with a question about lifestyle, not concrete. Do you want a flat lawn for kids, a terrace off the kitchen for dining, a vegetable garden, a fire pit area or simply safer access down the side of the house? Each of those uses sets different heights and widths for the level areas, and those levels decide where walls go and how tall they need to be.

This is why we plan retaining walls as part of the full landscape design rather than as a standalone repair. Steps, paths, drainage, irrigation and lighting all connect to the walls, and it is far easier to plan them together than to retrofit them later.

Choosing the right wall system

There is no single best retaining wall. The right system depends on height, soil, the load the wall is holding back and the look you want. The most common options on the Peninsula are:

• Poured concrete walls: the strongest option for tall walls and walls supporting driveways or structures. They can be finished with stucco, stone veneer or board-formed texture.
• Concrete block (CMU) walls: reinforced block walls that are versatile and cost-effective, usually finished with stucco, stone or tile.
• Segmental and gravity block walls: interlocking blocks that work well for low to moderate heights and curved layouts.
• Natural stone walls: dry-laid or mortared stone for a timeless look, well suited to estate gardens and traditional homes.
• Terraced walls: a series of shorter walls instead of one tall wall, which creates planting beds between levels and softens the look of a steep slope.

Drainage is what makes a wall last

Almost every failing wall we are called to replace has the same problem: water. Peninsula hillsides drain a lot of rainwater in winter, and clay soils hold it. When that water has nowhere to go, pressure builds behind the wall until it leans, cracks or bulges.

A properly built wall includes compacted base and footings, free-draining gravel behind the wall, filter fabric to keep soil out of the gravel, a perforated drain line at the base and outlets that carry water to an approved location. On properties with broader water issues, we often combine walls with drainage solutions such as French drains, area drains and dry creek beds.

Permits and engineering

In California, walls over four feet tall from the bottom of the footing, and walls that support a driveway, a slope above or a structure, generally require a building permit and an engineered design. Some towns also review larger exterior projects for design, and properties near creeks or protected trees can have additional steps. A contractor who handles engineering and permits as part of the project saves you time and makes sure the wall is built to code.

Repair, rebuild or replace?

Small cracks in a well-drained concrete wall can sometimes be repaired. But a wall that is visibly leaning, bulging, separating at joints or pushing soil through the face usually needs to be rebuilt. Timber walls that have started to rot are almost always replaced. During a site visit we look at the wall, the drainage behind it and the loads above it, then give you an honest recommendation.

Finishing the wall so it belongs

A retaining wall is one of the most visible structures in a hillside landscape, so the finish matters. We match walls to the home with natural stone, stone veneer, smooth or textured stucco or architectural block, then soften them with planting, cap stones, built-in seating and landscape lighting. The goal is a terraced landscape that looks designed, not engineered.

Retaining wall contractors on the Peninsula

Del Conte’s M&H Landscape Construction has built high-end residential landscapes on the Peninsula since 1972, with design and construction handled in-house. We build retaining walls throughout the area, including San Mateo, Burlingame, Hillsborough and Menlo Park, as well as Belmont and Los Altos Hills.

Frequently Asked Questions

When does a retaining wall need a permit in California?

Under the California Building Code, a retaining wall generally needs a permit when it is more than four feet tall measured from the bottom of the footing to the top of the wall, or when it supports a surcharge such as a driveway, a slope above or a structure. Cities and towns can add their own requirements, so it is worth confirming early in planning.

How long does a retaining wall last?

A well-built concrete, CMU or stone wall with proper footings and drainage can last for decades. Timber walls have a much shorter life, which is why so many older railroad-tie walls on the Peninsula are now being replaced.

What is the most common reason retaining walls fail?

Water. When a wall has no way to drain, water pressure builds behind it after heavy rain and slowly pushes the wall out of plumb or cracks it. Drain rock, filter fabric, perforated pipe and weep outlets prevent that.

Can a retaining wall be built in stages?

Yes. On larger hillside properties it is common to build the structural walls and drainage first, then add steps, planting, lighting and patios in a later phase. Planning the whole landscape up front makes that easier.

Planning a retaining wall or a terraced backyard? Call Del Conte’s M&H Landscape Construction at 650-870-1550 or send us a message to schedule a site visit.