Hardscape: Base, Pavers, Concrete, Walls, and Lighting
Hardscape Installation is about 21 percent of the official CSLB C-27 outline, covering flatwork, masonry, posts, fences, retaining walls, and water features, and the outline separately lists lighting controllers and transformers. This chapter works through the base that everything sits on, interlocking pavers, concrete flatwork and its joints, segmental retaining walls, accessibility, and low-voltage lighting, and it marks the points where the work leaves the C-27 classification.
Base Preparation Under Hardscape
A compacted aggregate base under pavers or flatwork provides a stable, load-bearing, well-draining foundation, and it is the component that decides whether the finished surface is still flat in five years. Base is placed in lifts of about four to six inches at optimum moisture, each compacted before the next, over a subgrade that has itself been compacted to the specified relative compaction. Base thickness follows load: a paver driveway needs a thicker base than a paver walkway, because it carries vehicle wheel loads that concentrate stress deep into the section. That is the reason a paver walkway settles into ruts within one season while the adjacent driveway holds up: the walkway base was either too shallow or inadequately compacted, and the surface is only reporting what is happening underneath. Base material also differs by system. Under standard pavers the base is a dense-graded aggregate, compacted to lock the fines and the coarse together into a rigid, low-permeability layer. Under permeable pavers the base is an open-graded clean stone with the fines washed out, so the layer has void space to store and pass water into the subgrade; that is what makes the system permeable, and it is why permeable and standard bases are not interchangeable. Permeable systems have a maintenance requirement that must be explained to the owner: a permeable paver parking area that stops draining after four years has almost always had its surface joints clogged by sediment, and the fix is to vacuum and replace the joint stone rather than to rebuild the base. Two installation practices belong at this stage because they cannot be added later. Sleeves and conduits are installed under a new driveway before paving, and beyond irrigation lines the crew should think about spare conduit for lighting and control wiring that may be added years later.
Interlocking Pavers
An interlocking concrete pavement is a flexible system: the pavers, the joint sand, the bedding sand, the base, and the edge restraint all work together, and removing any one of them breaks it. The bedding layer under interlocking concrete pavers is about one inch of bedding sand, screeded loose and left uncompacted, so that the pavers can be set into it and then vibrated down to a uniform plane. A thicker bedding layer allows differential settlement; a compacted bedding layer defeats the setting process. Edge restraint around the perimeter keeps the outer pavers from spreading and losing interlock, which is the mechanism by which a paver field stays tight: each unit is held by its neighbors, and the perimeter units are held by the restraint. Without it the field creeps outward, joints open, and the sand washes out. Laying pattern matters where turning loads exist. A herringbone pattern is preferred for pavers in a driveway because its interlocking geometry resists the creeping and shifting that turning vehicle tires impose, whereas a running bond can be pushed into waves. Joint sand is swept in and vibrated so the joints are full, since the sand transfers load between adjacent units. Where a hardscape surface must be built over the root zone of a mature preserved tree, the most protective approach is a pier-supported deck or a permeable surface set on grade, both of which avoid the excavation and compaction that would sever and smother roots.
Concrete Flatwork and Joints
Concrete cracks; the purpose of jointing is to decide where. A control joint, also called a contraction joint, is a planned line of weakness that concentrates shrinkage stress so the inevitable crack forms along the joint instead of wandering across the slab. Two dimensions govern it. Spacing is commonly taken as the slab thickness in inches multiplied by two to three, giving the spacing in feet, so a four-inch slab is jointed roughly every eight to twelve feet. Depth is about one quarter of the slab thickness, because the joint has to reduce the section enough to control where the crack initiates. An isolation joint is a different device with a different job: it separates the new slab from an adjoining fixed element such as an existing building slab, using compressible material full depth so the two can move independently without transferring stress. Placement and curing decide strength. When a driver arrives with concrete that has been in the truck longer than expected and asks whether to add water, the correct answer is no beyond the design mix, because added water raises the water-to-cement ratio and strength falls in direct proportion. And new flatwork is kept moist or covered for several days after placement so that cement hydration, the chemical reaction that develops strength, can continue; concrete does not dry to strength, it reacts to strength, and a slab that dries out early never reaches its design value. A decomposed granite path specified with a stabilizer uses a binder that holds the fines together and resists erosion, which is what keeps a DG path from washing into the lawn every winter.
Retaining Walls
A retaining wall holds back a soil mass, and the two things that make it fail are water and inadequate design for the load. A dry-stack, mortarless segmental block wall relies on interlock between the units, batter, meaning the setback of each course, and gravel backfill for stability, and a low wall of about 30 inches with level ground behind it is held in place primarily by the mass of the units, their setback, and the compacted base beneath them. Backfill immediately behind a segmental wall is clean drainage rock with a perforated pipe at the base and filter fabric separating it from the retained soil, and weep holes or a drainage system exist to relieve hydrostatic pressure behind the wall. That pressure is the usual killer: a block wall that leans outward after the first wet winter, on a site where the drain outlet has never flowed, has almost certainly had hydrostatic pressure build behind it as the drainage failed, because saturated soil pushes far harder than drained soil. The first course of a segmental wall is normally set below the finish grade in front of the wall to resist sliding and to prevent the toe from being undermined by erosion. The leveling pad itself must be a compacted, level base at the proper depth. Height and surcharge push a wall into engineering territory. A segmental wall at five feet of exposed height on a residential lot should be expected to require a permit and an engineered design from the local jurisdiction, and California jurisdictions commonly set their permit threshold at a stated height with a lower threshold where a surcharge exists, so confirm the local trigger rather than assuming a statewide number. A driveway directly behind a wall is a surcharge load, an additional load on the retained soil that the engineer must account for. Geogrid specified in a taller wall is a soil reinforcement laid in horizontal layers into the backfill; it reinforces the retained soil mass so that the soil and the wall act together as one gravity structure. A C-27 licensee who does not do engineered walls handles a wall over four feet by obtaining the engineered design and permit and using a qualified installer.
Steps, Paths, Accessibility, and Lighting
Outdoor steps are more comfortable and safer with a longer tread and a lower riser than indoor stairs, and a six-inch riser with a fourteen-inch tread is a common and comfortable garden proportion; on regulated or commercial work the applicable building code governs riser and tread dimensions and uniformity, so verify against the code in force. Accessibility rules apply on commercial sites. An accessible route's walking surface is generally limited to about two percent cross slope, and where a path exceeds five percent running slope it is treated as a ramp, which brings slope limits, landings, and handrail requirements with it. Those are code provisions in the California Building Code's accessibility chapter and the federal standards, so confirm the specific figures for the project type. Two small elements do quiet work. Bender board installed between a lawn and a planting bed holds the edge line and keeps bed material and turf separated. A mow strip between a lawn and a block wall gives a mower wheel a surface to run on beside the wall, eliminating hand trimming. A boulder placed as a landscape feature on a slope is buried roughly a third of its height and seated on firm compacted ground, so it looks like it belongs there and does not move. Low-voltage landscape lighting is inside the C-27 scope in a specific and limited way. Where a contract includes low-voltage path lighting fed from an existing exterior receptacle, the landscape crew sets the transformer and installs the low-voltage runs at that receptacle; the crew is working on the load side of a transformer at 12 or 24 volts, not on branch circuit wiring. Installing a new 120-volt branch circuit or receptacle to serve that transformer is electrical work for a licensed electrical contractor. The same boundary applies elsewhere in a landscape package: a C-27 asked to build a wood-framed pool house with a bathroom subcontracts it to contractors holding the appropriate classifications, while grading and preparing a yard for decorative treatment is squarely inside the C-27 classification.
Sequencing a Landscape Installation
The order of operations on a full landscape installation is dictated by what buries what and by what an inspector needs to see. Rough grading comes first, because everything else is set relative to the finished ground. Underground work follows: irrigation mainlines, laterals, sleeves under future hardscape, drainage lines, and conduit for lighting and controls, all installed while the ground is open and the equipment can still reach. Hardscape comes next, because base preparation and paving involve heavy equipment, spoil, and material staging that would destroy new planting, and because pavers and slabs are set to the finish elevations established at rough grade. Planting comes last, followed by the finish grading of planting areas, mulch, and turf. That order also matches the inspection sequence, which is often what drives a landscape schedule: inspection holds on grading and on underground work before cover are the constraint that most often determines the timeline, because a jurisdiction may require an open-trench inspection before backfill, and a crew that covers work early may be required to uncover it. Two documentation habits close the job. Photograph the underground work before backfill, so you can show where lines run and prove the installation. And at final walkthrough, deliver a package the owner can maintain the system from: as-built drawings showing valve locations, the irrigation schedule, and a parts list, which is far more useful for future maintenance than a warranty letter alone.
Last updated: September 2026