Redwood handles Peninsula winter rain well as long as someone seals it, and composite handles it without any help at all, which is the real difference between the two. Both materials can last on the Peninsula. The question is not which one is stronger. It is which one matches the amount of upkeep you will honestly do once the rain starts.
Here's the short version:
- Redwood costs less up front, looks and feels natural, and needs a dry weekend for sealing, which is hard to find between December and March.
- Composite costs more up front and needs virtually no maintenance, no sealing, and does not splinter.
- Shade, fog and poor drainage matter more than the material itself, so a north facing hillside deck in San Carlos and a flat lot in Foster City call for different thinking.
- Fall is the last reliable dry stretch to build a new deck or seal an existing one before the wet months.
What a Wet Peninsula Winter Does to a Redwood Deck
Redwood is a good choice here for a reason. It resists rot and insects naturally, it is stable, and it takes a finish well. What it does not do is stay the same color and texture without attention.
Checking
As redwood takes on water and then dries out, the surface moves. That cycle opens up fine splits along the grain, usually on the top face of boards where sun and rain hit hardest. Checking is mostly cosmetic at first. Left alone through several wet seasons, those openings hold water longer and give the surface more places to break down. A sealed board moves less because it absorbs less.
Graying
Untreated redwood goes silver gray. Some homeowners want that. Others are surprised by how fast it happens on the exposed side of the deck while the covered side stays reddish, which leaves a deck that looks like two different projects. Sealing slows the change and keeps the color more even.
Mildew on the shaded side
This is the part people underestimate. The north side of a deck, the strip behind a planter, the section tucked under an overhang, these areas stay damp long after the rest of the deck dries. Green and black growth follows. It is not structural damage, but it is slippery, it stains, and it comes back every winter until drainage or airflow improves.
The sealing window
The honest problem with redwood is scheduling. Sealing works when the wood is dry and the weather stays dry while the finish cures. On the Peninsula, that pairing is easy in September and October and rare in January. A homeowner who plans to seal in winter usually ends up not sealing at all, and the deck pays for it the following year.
How Composite Handles the Same Winter
Composite decking is built to skip the maintenance cycle. It does not need sealing, it does not splinter, and rain does not open up the surface the way it opens up wood. For anyone who knows they will not be out there with a brush and a can every fall, that alone settles the decision.
Two things to know before you assume composite is automatic. First, the price is higher at the start. You are paying up front for the work you will not do later. Second, composite holds temperature. A dark board in shade stays cold underfoot on a foggy morning, and a dark board in full afternoon sun gets hot. If your family uses the deck barefoot, lighter colors are worth looking at.
Composite also still collects the same mildew that wood does when it sits in constant shade and standing water. The difference is that it cleans off a hard surface rather than soaking into open grain.
A backyard deck after a rain, with water beading on the surface and standing damp along the shaded edge.
Local Conditions That Change the Answer
Materials behave differently across a few miles on the Peninsula.
Coastal fog in Pacifica and San Bruno. Fog is not rain, but it keeps surfaces damp for long stretches without ever really wetting them enough to rinse anything off. Decks in these neighborhoods stay in a low grade damp state much of the year. Wood here wants a good finish and good airflow underneath. Composite here wants a wash now and then so growth never gets a foothold.
Flat lots in Foster City. Flat ground drains slowly. Water sits under the deck, around post bases, and along the perimeter. The decking surface matters less than what is beneath it. Proper footings, framing that sheds water, and a plan for where runoff goes will determine how the deck ages more than the choice of board.
Hillside decks in San Carlos. A deck on a slope often sits against a bank, with one side that never sees direct sun. That shaded side is where mildew starts and where a wood deck ages first. It is also where structure becomes the real conversation, since hillside builds involve posts, beams and sometimes engineering. If that describes your yard, multi-level deck options for hillside properties covers how these layouts get planned.
| Consideration | Redwood | Composite |
|---|---|---|
| Up front cost | Lower | Higher |
| Sealing | Needed, on a dry stretch | Not needed |
| Surface after years of rain | Can check and gray | Stays consistent |
| Splintering | Possible as it weathers | Does not splinter |
| Feel underfoot | Natural, warm | Holds cold in shade, heat in sun |
| Shaded areas | Mildew soaks into grain | Mildew washes off surface |
| Best for | Owners who enjoy upkeep and want real wood | Owners who want to build once and leave it |
A Simple Way to Choose
Ask yourself one question and answer it truthfully: will you seal this deck every year or two on a dry fall weekend?
If yes, redwood is a good value and it will reward the effort with a look composite does not quite match. If the answer is probably not, or if the deck is a rental, a second property, or a hillside surface you rarely walk on, composite removes the maintenance question entirely and that is worth the higher start.
A middle path exists too. Some homeowners use composite on the flat walking surface and redwood for railings, benches and trim where hands and eyes land. Our Decks page walks through the options, and planning a new deck in South San Francisco covers the layout decisions that come before material.
Talk to A-1 Fence and Deck Before the Rain Arrives
A-1 Fence and Deck Inc. has been family owned since 1978, serving South San Francisco, Pacifica, San Bruno, Foster City, San Carlos and the rest of the Peninsula. We build custom decks in both wood and composite, from simple platforms to multi-level designs with built in seating, and we handle the permit process as part of the service. Structural engineering is arranged when a site calls for it.
Fall is the last dependable dry stretch for building a new deck or sealing an existing one. Ask us for a free estimate or call (650) 873-7272.
FAQs
Do I need a permit for a deck?
Most decks require permits. We handle the permit process for you as part of our service, so you are not the one tracking paperwork.
Wood or composite, which is better?
Wood costs less upfront and has a natural feel. Composite costs more but requires virtually no maintenance. We can help you decide based on your priorities, your sun exposure, and how much upkeep you want to take on.
Can a deck be built on a shaded, damp part of the yard?
Yes. The key is drainage and airflow under the structure so water does not sit. In deep shade, composite is often the easier long term surface because mildew stays on top rather than working into the grain.
Is it too late in the year to seal my redwood deck?
Fall is usually the last dry window. The wood needs to be dry when the sealer goes on and the weather needs to stay dry while it cures, which is hard to count on once the winter pattern sets in.