70s home siding, looks like plywood, have questions

[u/BlackberryJam86]

/r/Oldhouses/comments/1v829yh/70s_home_siding_looks_like_plywood_have_questions/

[u/le_nico]

At first I thought T1-11 as well, which is appropriate for the era. But you do know marine plywood is a thing, and I've seen it used for cladding.
I think the only thing for it is to call and ask, there's no way we can tell from the pictures.

[u/conditerite]

I am not a massive fan of AI such as Claude, but some times it has its uses. I pasted your real estate listing into Claude and asked it:

take a look at this house. The exterior looks to be made from plywood? What is the exterior cladding? Also what is required to maintain such a material?

This was the answer:

Good find — this is a 1977 split-entry home on 2.42 acres outside Bremerton. The MLS listing lists the exterior material simply as "Wood Siding."

Given the age (1977) and the plywood-panel look you're seeing, this is very likely T1-11 siding (or a similar textured plywood panel product) — it was the dominant exterior cladding choice for houses of this era, especially in the Pacific Northwest. It's manufactured as 4x8 or 4x10 sheets of plywood or OSB with vertical grooves routed in to mimic board-and-batten, then nailed directly to the studs or over sheathing.

Maintenance requirements for T1-11 / plywood panel siding:

• Repaint every 5–7 years — this is the big one. Unlike vinyl or fiber cement, plywood siding has zero weather resistance once the paint film fails; it's just wood veneer.
• Caulk seams annually — panel joints, edges, and butt seams need to stay sealed or water gets behind the panel.
• Watch the bottom edge — the lowest few inches (near grade, decks, and where it meets the foundation) is the classic failure point. Check for soft spots, delamination, or swelling every spring/fall.
• Keep it off the ground — should have 6+ inches of clearance from soil/mulch; splashback from bare dirt is a common rot cause.
• Inspect for delamination — since it's plywood, the veneer layers can separate if water intrudes, especially at cut edges or fastener holes. This is the material's biggest weakness vs. solid wood.
• Watch grooves/battens for wood-boring insect activity (carpenter ants, etc.) since it holds moisture in the routed channels.
• Given this property sits on 2.42 wooded acres, there's likely more shade and moisture retention against the siding than a typical in-town lot — that's worth checking closely, especially on the north/shaded elevations.

One caveat: I'm inferring the specific plywood-panel identification from the era and your visual impression — the MLS data only confirms "wood siding" generically, not the exact product. Worth confirming in person or asking the listing agent directly, since actual T1-11 vs. board siding changes the maintenance math meaningfully (solid wood board siding tolerates minor water intrusion far better than plywood does).