Which material lasts longest a few streets from the Pacific? The answer has a twist at the end, so read the last section before you sign anything. The five choices still deserve going through in turn, because they fail in different places, and knowing which failure you are buying is most of the decision.
Steel, where gauge tells you more than the badge
Steel is what most doors on this coast are made of, and the figure to ask for is the gauge. Gauge counts backwards, so 24 gauge is thicker metal than 27 gauge. A thin single skin panel on a double opening flexes as it lifts, and flexing splits the paint film at the joints and edges long before the flat faces show anything. Once the coating opens, salt has bare metal. Ask what is under the color as well: a hot dipped galvanised base with a baked primer and topcoat, not paint applied straight to mild steel. Then ask where the cut edges are, because those are where a coastal steel door starts to go, on the ends of each section and along the bottom rail that stands in hose water.
Insulated steel, and the reasons that are not about heat
An insulated door is two steel skins with a core between them, and it does better here for reasons unrelated to temperature. The sandwich is stiffer, so a wide door flexes less and the finish survives longer. It runs quieter, which counts in Ocean Hills and under any bedroom over a garage. Polyurethane bonded to both skins beats a loose polystyrene board, because water that finds its way in has nowhere to pool. The weak point stays the same as any steel door, the bottom section and its edges, so specify a good bottom rail and keep the seal in good order. California Title 24 makes insulation worth pricing anyway on an attached or conditioned garage.
Aluminum and glass
Full view aluminum and glass suits the modern rebuilds and the hillside houses on Fire Mountain, and the frame is genuinely well suited to marine air, since anodised aluminum does not rust. The catch is everything the frame touches. Hinges, roller stems, brackets and fasteners on that door are all steel, and a steel screw sitting in an aluminum frame in salt air sets up galvanic corrosion that eats at both. Stainless fixings, or fixings properly isolated from the frame, are the difference between a door still looking crisp at fifteen years and one weeping white bloom from every joint by year five.
Composite and fibreglass
Composite and fibreglass skins handle salt well for the obvious reason that they are not steel. No chalking, no pitting, no rust bleeding from a cut edge. Fibreglass is usually formed over a steel frame, so the frame still wants to be galvanised. The honest limits are color and impact. Years of west facing sun will fade a dark skin, and a composite panel that takes a real knock tends to crack rather than dent, which means a panel replacement at an estimated $265 to $580 instead of some filler and paint. For a door that faces the ocean and gets little attention, it is a sensible buy.
Real timber, and the cycle you are committing to
A timber door on one of the 1920s to 1950s bungalows near the water can look better than anything else on the block, and it can also become the most demanding thing on the house. Wood does not rust, which is the appeal. It does move with humidity, and it lives entirely on its finish. On this coast that means a marine grade varnish or a full paint system, checked every year and recoated every two to four depending on how much afternoon sun the door takes. Miss two of those and water gets behind the finish at the joints, the stiles swell and the door stops sitting square in its opening. Timber is heavy as well, so it works the springs and the opener harder than any other option here.
A word about color and HOA rules
Worth raising before you fall for a door. Master planned tracts including Rancho Del Oro, Arrowood and Ocean Hills have appearance guidelines, so the color and often the panel style have to match an approved scheme, which narrows the material choice before any of the above matters. Read the guidelines first. Color is also a durability question on a west facing driveway, since a black or deep bronze finish runs hotter and chalks under ultraviolet sooner than a mid tone.
The answer nobody in a showroom leads with
The panel decides how the door looks in ten years. The hardware decides whether it still opens. Springs, lift cables, rollers, hinges, drums and bottom brackets are steel on every door described above, no matter what the skin is, and they are what actually fails in Oceanside CA. So when you compare two quotes, look past the panel and ask what is specified behind it: galvanised lift cables, plated stems with sealed nylon wheels, coated spring wire, stainless or coated fasteners into the wall, and a bottom seal rated for sun as well as water. That package adds roughly 10 to 20 percent to the hardware line and it is the best money on the page for anyone within a mile of the water.