An Engineering Insight authored by SK&A Principal Justin Long, PE, RBEC, BECxP. Follow Justin on Linked In.
The Hidden Movement Behind Facade Performance
As wood-frame buildings rise taller, one subtle – but critical – movement demands more attention: cumulative shrinkage.
Shrinkage occurs primarily perpendicular to the grain as wood dries below its fiber saturation point. While it may only measure a few tenths of an inch per floor, that movement accumulates over multiple stories, influencing everything attached to the structure – from facade claddings to windows and mechanical systems.
How Shrinkage Impacts Facades and Openings
Over time, as framing members dry and contract, their vertical shortening can:
- Compress veneer supports and window openings, leading to cracked sealants or binding sashes.
- Distort flashing slopes at window heads and sills, undermining drainage.
- Stress cladding transitions, especially where expanding materials (like brick veneer) meet other cladding systems.
The result? Even small unaccounted movements can translate to visible facade distress, water intrusion, or loss of air-tightness.
Detailing Strategies That Work
To manage these movements effectively, designers must anticipate differential movement between the wood frame and the exterior envelope:
- At Brick Veneers – Provide vertical gaps between the top of the veneer and the underside of window sills or flashing, filled with compressible sealants or backer rods sized for the full expected differential movement.
- At Window Heads & Jambs – Design flexible sealant joints and consider delaying caulk installation until framing moisture stabilizes. Use counter-flashing or double-flashing systems to accommodate vertical movement.
- At Cladding Transitions – Leave a movement gap at material changes (e.g., fiber cement to brick) and protect it with flashing and flexible filler to maintain drainage continuity.
- At the Structural Interface – Consider semi-balloon framing or reduced cross-grain layers to minimize cumulative shrinkage per floor.
The Takeaway
Wood is dynamic – it moves with its environment and shrinks over time. Thoughtful facade and opening details aren’t just good practice; they’re essential for ensuring long-term performance and appearance.
As mid-rise wood projects continue to expand, designing for shrinkage isn’t an optional consideration – it’s part of what makes a durable, resilient building.
This insight was originally published by Justin Long, PE, RBEC, BECxP, on Linked In. View the original post and add your own comments.
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