Design decision
Why this idea works
A rain garden just below the terrace intercepts runoff before it can pool or run off-site, letting the ground soak it up and feed the planting. It reads as an attractive planted edge while doing real drainage work, so the terrace stays dry and the rain becomes a resource rather than a nuisance.
- The tradeoff
- The layout sets a clear direction, but it also commits the project to fixed relationships. Size the rain garden and its overflow to the terrace runoff.
- How to measure it
- Conceptual range: the terrace plus a separately measured rain-garden basin.
On your property
Plan it for your site
Keep the terrace sloped to shed cleanly into the rain garden, and detail the edge so it does not undercut. Size the basin and an overflow for heavy storms, and plant it with species that tolerate both standing water and dry spells.
- Grade the terrace so runoff sheds cleanly into the rain garden.
- Size the basin and an overflow for heavy storms, not just light rain.
- Choose plants that tolerate periodic standing water and dry spells.
Before forms are set
Build implications
- Confirm before estimating Terrace grading that feeds the basin.
- Confirm before estimating Basin and overflow sized for real storms.
- Confirm before estimating Rain-garden planting suited to wet-and-dry cycles.
- Measure the site and establish elevations Record boundaries, thresholds, grade changes, utilities, and the dimensions of vehicles, furniture, equipment, or structures that affect the layout.
- Test how the space will be used Check walking routes, turning paths, door swings, working clearances, maintenance access, and the route back to the house or street.
- Resolve drainage, services, and structural support Decide where water goes and coordinate drains, conduit, irrigation, fuel, electrical work, footings, and independent supports before forms are set.
- Define and estimate each concrete element Confirm the slab or footing section, base, joints, edges, and finish, then estimate simple measurable fields separately from steps, walls, drains, and supported features.
Prevent these problems
- Calling a retaining element decorativeA wall or planter that holds soil or water needs support, reinforcement, drainage, and often professional review.
- Hiding runoff with plantingA rain garden, swale, or planted edge must receive water intentionally and have a safe overflow route.
- Choosing the finish before defining the jobSeat walls, planters, edging, terraces, and retaining walls may look related but carry very different loads and details.
Next step
Turn the idea into your estimate
Enter measurements from the property. The conceptual image does not provide a takeoff.
Estimate a similar concrete featureQuestions this idea raises
What is a rain garden?
A shallow planted basin that catches and soaks up runoff, easing drainage and adding greenery, a widely used green-infrastructure detail. Size it and an overflow to the runoff.
Will a rain garden stay soggy?
A well-designed one drains between storms and uses species tolerant of wet and dry, so it should not stay waterlogged. Sizing and plant choice keep it healthy.
- Best when
- Drainage-aware features
- Reconsider when
- Reconsider the idea if retained soil or water, footing and reinforcement needs, drainage, and long-term access cannot be resolved on the property.
- Verify first
- Size the rain garden and its overflow to the terrace runoff.
- Professional input
- Landscape or concrete contractor; engineer for retaining or structurally loaded work
Sources and further reading
- American Concrete InstituteTechnical context for seat walls, planters, and small structural concrete elements.
- EPA: Types of Green InfrastructureContext for rain gardens, planted swales, and water-aware transitions beside concrete.
- NRMCA CIP 6: Joints in Concrete Slabs on GradeA starting point for jointing terraces, landings, and larger flat features.
