10/06/2026
Building Science in Action! 🏠☀️
Same roof, same day. Top photo: 10am. Bottom photo: noon.
See those grid lines in the morning shot? That's the outline of the roof sheathing panels telegraphing through the shingles. By noon, they're gone.
Here's what's happening. Roof sheathing panels (usually OSB) are supposed to be installed with a 1/8" gap at every edge so they have room to expand. When they're butted tight, they soak up moisture overnight, swell, and push their edges up into the shingles. As the sun dries them out during the day, they shrink back down and the lines disappear.
Why it matters: that daily swelling and shrinking stresses shingles and fasteners along every seam, can cause early wear, and may affect your shingle warranty. And here in the Pacific Northwest, our damp mornings and long wet season mean this cycle repeats a lot.
