A deck with a view of the ocean asks a lot of a few pieces of wood and steel. It hangs off a house, often over falling ground, and spends its life in damp, salty air. When it is built well and looked after, it can do that for a long time. When something is missed, the failure tends to be quiet until it isn’t.
This entry looks at the deck as a structure: what holds it up, what the coastal air does to its metal parts, and what Del Mar’s bluff rules say about decks near an edge.
What holds a deck up
The California Residential Code treats a wood deck as its own load path. Section R507 requires decks to be designed for the live load set elsewhere in the code, and lays out how that load reaches the ground:
- Footings. Decks must be supported on concrete footings or another approved system designed for the loads. The code sizes prescriptive footings from the area of deck each one carries and the bearing capacity of the soil beneath it.
- Posts and beams. Carry the joists down to the footings.
- The ledger. Where a deck attaches to the house, the ledger board is bolted or lag-screwed to the band joist. The code states plainly that ledgers shall not be supported on stone or masonry veneer.
- Lateral connection. Where the code’s prescriptive detail is used, hold-down devices rated at not less than 1,500 pounds go in at least two places, within 24 inches of each end of the deck, tying the deck back to the house so it cannot pull away.
- Guards. Must carry their loads continuously into the deck framing.
On a slope, the first item is where the thinking starts. The prescriptive tables assume soil of a known bearing capacity on reasonably level ground. A footing near the top of a slope, in loose fill, or close to a retaining wall is a different situation, and usually one that calls for site-specific design. Our bluff and hillside homes page discusses those conditions in general.
What salt air does to the metal
Most of a deck’s strength is in the wood. Most of its connections are metal: nails, screws, bolts, joist hangers, post bases, hold-downs and flashing. Those are the parts that the coast works on.
The code’s fastener table for decks requires hot-dip galvanized or stainless fasteners, and for metal connectors it lists G185 galvanized steel or an equivalent hot-dip coating, with stainless steel as the alternate. Flashing must be corrosion-resistant metal at least 0.019 inch thick, or a compatible nonmetallic material.
FEMA’s Technical Bulletin 8, on corrosion of connectors and fasteners in coastal areas, adds the reasons. It explains that salt spray is heaviest near breaking waves and drops off over the first 300 to 3,000 feet inland, though accelerated corrosion has been measured 5 to 10 miles from the shore. It reports that metal on the side of a building facing the ocean corrodes much faster than metal facing away, and that partially sheltered places, specifically the undersides of decks and walkways, can corrode faster than open surfaces because rain does not wash the salt off.
That last point is the one owners tend to overlook. The top of an ocean-view deck gets rinsed every winter. The hangers and bolts underneath do not. Our salt air and concrete corrosion page covers the same chemistry as it affects concrete and reinforcing.
Where water gets in
Wood under a deck fails from water, not from age alone. A few places concentrate it:
- The ledger joint. Where flashing over the ledger is missing, torn or reversed, water runs behind it and into the house’s band joist.
- Post bases. End grain sitting in a pocket of water or soil.
- Under solid surfaces. Decks with waterproof membranes over them hide the framing entirely.
- Irrigated planters. Built on or against the deck.
- Downhill drainage. Water from the deck surface, discharged onto the slope below the footings.
The last item connects the deck to the hillside. Our post on hillside drainage in Del Mar follows water from roof to street.
Decks near a coastal bluff
Del Mar’s Coastal Bluff Overlay Zone, Chapter 30.55 of the municipal code, names decks directly. Its definition of accessory structures includes above-grade decks or patios. The chapter then sets these rules for the bluff top:
- New or redeveloped principal or accessory structures, including new supporting foundations or supports for existing structures, are to be set back a minimum of 40 feet from the top edge of the coastal bluff.
- New fences, windscreens and benches are to be set back at least ten feet, and where they sit inside the 40-foot line, they are to be built primarily above grade with lightweight materials and without grading or continuous foundations.
- No grading is allowed within 40 feet of the bluff top edge.
- Landscape plans for projects requiring the overlay’s permits are to ensure no new irrigation within 40 feet of the bluff edge, and removal of existing irrigation there.
- Drainage plans for graded projects are to carry water away from the bluff face, prepared by a licensed civil engineer and reviewed by the City Engineer.
Inland slopes and canyon edges fall under a separate overlay, Chapter 30.52, with its own review requirements.
These rules describe what the code asks of an application. They do not say how any particular application will be decided, and nothing here should be read as a prediction. What they do suggest is that replacing a deck’s footings near a bluff is not a routine swap, and that the conversation with the City should come early. Our design review page explains how Del Mar reviews structural work.
Condominium decks
Where a deck belongs to a condominium building, it may fall under Civil Code 5551. That statute requires associations to have a licensed structural or civil engineer, or an architect, inspect a statistically significant sample of exterior elevated elements at least every nine years. It covers load-bearing components of decks, balconies, stairways and walkways more than six feet above ground and supported substantially by wood, along with their flashings, membranes, coatings and sealants.
A look underneath
An owner can learn a good deal with a flashlight:
- Rust staining or flaking on hangers, bolts and post bases
- Soft or dark wood at the ledger, post bases and joist ends
- Gaps between the ledger and the house
- Footings that have tilted, cracked or lost soil around them
- Water marks below the deck surface
- Guards that move when pushed
Any of these is a reason for a closer foundation inspection of the deck and the ground under it.
What shapes the scope of deck work
- Distance from a coastal bluff edge or slope
- Footing condition, soil and slope below
- Connector and fastener corrosion
- Ledger attachment and flashing
- Hidden framing under membranes or solid surfaces
- Permit and overlay requirements
- Access on a steep lot
A contractor can open, document and repair what the code covers prescriptively, and coordinate with licensed engineers as needed for footings on slopes and anything near the bluff.
To have an ocean-view deck anywhere in Del Mar looked at from the footings up, request a Free Quote.