New Construction in Malibu, Dry Below Grade
New house construction in Malibu that keeps water out of below-grade walls with a membrane, drain board and a footing drain, reviewed by the City of Malibu.
Where a new Malibu house steps into the ground, the walls below grade need their own plan for water. Rain soaks into the soil and presses against concrete, and on a coastal lot damp air can keep surfaces wet longer. We wrap those walls in a waterproof membrane, add a drain board to relieve the pressure and lay a perforated footing drain that carries water to an approved outlet. The City of Malibu reviews the drainage design.
The wall assembly
Below-grade concrete gets a fully adhered membrane, lapped and sealed at every corner and joint. A dimpled drain board covers the membrane, giving water a gap to fall through to the footing. At the base, a perforated pipe in washed gravel wrapped in filter fabric collects that water and slopes to a sump or a solid outlet line. Where a wall meets a slab, a waterstop is cast into the joint. We photograph the membrane before backfill so a record exists after the soil is back in place.
Where the water goes
Collected water and roof water need somewhere safe to land. If the lot slopes, an outlet that dumps onto the ground below can cause erosion, so the civil engineer designs an energy dissipater or a line to the street. A lot may also have an onsite wastewater system, and drain lines are kept apart from it. Fire hazard maps cover parts of Malibu, so gutters on a mapped lot are covered and downspouts are metal. The inspector sees the drain pipe and the membrane before anything is buried.
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New Construction in Malibu: questions
We want the survey with topography, the geotechnical report and any earlier drainage plans for the parcel. Since the coastal zone may cover your lot, we check that status first, because it can add a separate approval. Tell us where water collects after rain. Those observations guide the below-grade design.
Design coordination, the civil and structural engineering, any coastal approval and the city permit are priced together first. The build follows as its own estimate in order: grading, foundation and below-grade walls, framing, roof, rough trades and finishes. Waterproofing and drainage lines are written out separately, each with the product named.
We manage the whole group. The surveyor maps the lot and its grades, borings follow from that map, and the civil and structural engineers design with both reports open. We keep a single set of drawings current and route each review comment from the City of Malibu to the consultant who owns that sheet.
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Tell us about the property and what you have in mind. We reply with a written next step.