Why are my cedar ceiling planks gapping so much after a solo install?

Cedar tongue-and-groove is notoriously fickle with moisture, and those gaps near the French doors are likely because the boards weren't fully acclimated to the exterior humidity levels before you pinned them. When wood moves from a dry storage area or a shop to an open-air porch, it needs at least a week to reach equilibrium. Using a **15-gauge nailer** is fine for the holding power, but if you're nailing through the tongue and the board shrinks, that shoulder is going to pull away and expose the raw wood or leave a visible gap. On those long runs, I usually try to leave a penny-width gap every few courses to give the wood a place to expand without buckling, though that doesn't help much with the shrinking you're seeing now. Working solo on a vaulted ceiling is a nightmare without a few jigs. To keep those long boards straight and held in place while you're at the other end, try screwing a few **cleats or 'deadmen'** into the rafters about an inch below your working line. You can slide the board onto the cleat, and it’ll hold the weight while you focus on the tongue-and-groove alignment at your end. Another trick is using a few scrap pieces of the cedar as 'push blocks.' Cut a small groove into a scrap, fit it over the tongue of the board you're installing, and use a quick-clamp against the rafter to squeeze it tight into the previous row before you fire a nail. And check your layout every three or four rows by measuring back to the starter wall or the ridge. It’s easy to get a slight curve in the middle of a 16-foot run if you're just eyeballin' it or relying on the tongues to bottom out perfectly. If you find you're getting off-parallel, you can slightly 'cheat' the next few boards by not seating the tongue all the way home on one end. Just a 1/32nd of an inch over five boards will get you back to square without it being visible to the eye. Since you're already seeing movement, you might have to wait for the humidity to stabilize before deciding if you need to pull a few boards. If the gaps are consistent, sometimes a bit of color-matched wax filler or a tinted finish can hide the light-colored wood exposed by the shrinkage. But next time, definitely let that cedar sit on-site for a while and use those temporary cleats to save your back and your sanity.

Honestly, sounds like you fought that 1x6 cedar way harder than you needed to. For solo ceiling runs, I never leave the shop without my Titen HDs or some GRK trim screws to set up a temporary ledger. But the real game changer is the Stabila 80 AS-2 level—if you aren't checking for plumb every three courses, you’re just chasing your tail. Also, switch that 15-gauge out for a Senco FinishPro 25XP next time. The 18-gauge brads give the wood a little more room to breathe than those fat 15-gauge shanks, wich ussually just split the tongue and cause the exact 'creeping' gaps you're seeing now near the doors.

I had the same back-breaking struggle on a vaulted porch last summer. I stopped trying to balance those 14-footers and started using a 'third hand' support pole—the kind used for drywall. It takes the weight so I can focus on the groove. To keep the lines straight, I actualy use a cheap laser line across the rafters. It shows me exactly where my leading edge needs to be without constantly pulling a tape. For the movement, I started pre-staining the tongues before install. That way, when they shrink in the cold, you don't see that ugly raw wood line.

I'm just starting out and honestly, reading all this makes me realize how little I actualy know about wood movement. You mentioned using a scrap piece as a 'push block' with a clamp—does that ever crush the tongue or mess up the wood if you squeeze it too hard? I'm also curious about those 'deadmen' cleats. Do you just screw them right into the finished rafters and then have to patch the holes later, or is there a trick to avoid leaving marks on the structure?

Quick update — I appreciate the advice on the 'third hand' poles. I picked a pair up and they whould’ve saved me alot of ibuprofen. I’m still worried about the movement near the doors, though. One of you mentioned checking for plumb every few runs; has anyone found that using trim screws instead of 15-gauge nails helps minimize that seasonal shifting with cedar?