4 years in: cypress vs sapele siding on the same beach house. One side is failing.

Built our beach house on Hatteras in 2021. Architect wanted a material study so we did the east face (ocean-facing) in sapele and the west face (sound-facing) in cypress. Same contractor, same primer, same topcoat, installed within the same week. 4 years later the difference is not subtle: Cypress (west/sound side, less exposure): Paint adhesion failing in 3 areas, one board has soft rot starting at a horizontal joint, generally looks tired. Already needs repaint. Sapele (east/ocean side, MORE exposure): Finish still bonded perfectly. Zero rot anywhere. Zero cupping. The salt spray basically washes off and the wood underneath is rock hard. The sapele was about 40% more expensive in material ( vs for the cypress). But the cypress side needs in maintenance now at year 4, and will need full repaint by year 6. The sapele side needs a hose-down. Ordered the sapele from a specialty hardwood supplier, they milled it to a rabbeted bevel profile to match the architect's detail. The stuff came at 9% MC and hasn't moved. I'm now planning to reside the cypress walls in sapele next year. Should have just done the whole house. If you're coastal: cypress is fine for trim and interior. For siding taking salt air, go tropical hardwood. The upfront premium pays for itself by year 5.