Rain, snow, and wind-driven water test exterior defenses, while showers, cooking, and even plants add interior humidity that can push vapor through cracks. Construction moisture from fresh screeds and plaster also matters. Leaks are memorable, but slow vapor drives are sneaky and relentless. Understanding these sources helps prioritize defenses, like pressure-managed cladding, balanced ventilation, controlled interior humidity, and careful sequencing that limits wet trades near timber. Identify the likely sources in your climate and you’re halfway to success.
CLT holds and releases moisture in a forgiving, yet limited, way. Panels can adsorb short-term spikes, then dry when conditions improve, provided there is a safe path out. Directional diffusion, surface finishes, and layer permeability matter. A vapor-retarding primer can protect interiors while a ventilated cavity encourages outward drying. Too many low-perm layers trap water; too few permit inward drives. Recognizing this balance lets you pair CLT’s mass with smart barriers, preserving strength, dimensional stability, and indoor air quality.
Select a robust, self-adhered or mechanically attached WRB that tolerates temporary exposure and bonds well to CLT or sheathing over CLT. Continuity at corners, parapets, and floor transitions matters more than brand. Tape panel seams, seal fasteners, and pressure-test with blower-door verification before finishes go on. A tight air barrier reduces interstitial condensation and energy loss, while simplifying vapor control. Train installers, photograph critical steps, and document repairs immediately. Reliable continuity is less about luck, more about verified process.
A ventilated cavity behind cladding transforms the wall into a forgiving system. Even thin, 10–20 millimeter gaps can drastically improve drying by promoting airflow and gravity drainage. Provide bottom and top openings with insect screens and leave clear paths around vertical battens. Avoid compressing the cavity with insulation or blocking it with sealant blobs. Consider capillary breaks at furring attachments and use durable flashing at transitions. In wet climates, a vented, drained cavity is the unsung hero of longevity.
Decide early between vented and compact roofs. In cold climates, a smart vapor retarder below insulation can limit winter drives without blocking summer drying. Above, high-quality membranes with welded seams and robust edge metal resist ponding and uplift. Penetrations need boots and curbs that rise above finished surfaces. Insulation thickness and placement control dew points within safe ranges. Commit to regular inspections of drains and scuppers, removing debris after storms to preserve performance and avoid hidden, progressive wetting.
Balconies tempt water inward through door thresholds and structural connections. Use thermal and moisture breaks to isolate the panel, slope surfaces away, and provide drip edges. Consider cassette balconies that bolt to brackets rather than penetrating the CLT. Flash and counter-flash with clear paths to daylight. Guardrail posts should mount on raised plates, not through membranes. Test door pans with hose tests before finishes. Small, careful moves here eliminate chronic staining, swelling at edges, and premature replacement of exterior assemblies.
Wet rooms succeed when layers overlap intelligently. Use bonded waterproofing membranes under tile, integrate drains with clamping flanges, and wrap up walls to capture splash. Seal around mixers, niches, and supply lines with gaskets that flex but remain airtight. Ventilate with controlled exhaust linked to humidity sensors, encouraging quick drying after use. Provide access panels to valves and traps for easy inspections. A carefully layered system forgives daily soaking and protects CLT cores from cumulative, invisible moisture loads.
Regulators want proof that assemblies can shed and dry moisture safely. Compile product data, test reports, blower-door results, and hygrothermal simulations that demonstrate performance in your climate. Show continuity diagrams for control layers and field photos of key details. Provide maintenance guidance that aligns with code expectations. When submittals connect design intent, verified construction, and operational care, approvals become smoother, inspectors become allies, and everyone gains clarity about how the home will perform through storms, seasons, and decades.
A coastal townhouse endured a brutal winter with weeks of rain, yet stayed dry thanks to a simple, ventilated rainscreen and rigorous sill pans. Another project learned the hard way that unsealed balcony bolts wick water; a retrofit added sleeves and new flashings, resolving stains. Monitoring on a mountain cabin revealed brief winter spikes that dried each spring, validating a balanced vapor strategy. These stories show that disciplined basics often outperform complexity, especially when crews are trained and details are verifiable.
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