In This Guide
Wind-driven rain intrusion is a different animal from ordinary rain. When Pacific storms send rain sideways at 40 miles per hour, water attacks walls, windows, and roof edges that vertical rainfall never touches. A home that stays perfectly dry in calm rain can leak badly during a windstorm, and in Lynnwood, wind-driven rain is a fact of life every fall and winter.
Here is how wind-driven rain gets in, where homes are most vulnerable, and how to defend yours.
What Is Wind-Driven Rain Intrusion?
Wind-driven rain is rain pushed by wind against vertical and sloped surfaces with real pressure behind it. That pressure forces water through gaps, cracks, and joints that gravity alone could never penetrate: under siding laps, around window trim, beneath shingle tabs, and into tiny openings in flashing. Building scientists measure it as rain load on a wall, and windward walls in our region can receive several times the rain of leeward walls during a single storm.
How Wind-Driven Rain Enters Homes
- Through siding joints. Pressure pushes water up and under horizontal siding laps and through butt joints.
- Around windows and doors. Wind forces water past weatherstripping and into gaps between the frame and the wall.
- Under roof edges. Wind lifts shingle tabs at eaves, rakes, and ridges, driving water beneath them.
- Through vent openings. Attic vents, dryer vents, and range hood vents can admit wind-blown water.
- At deck and ledger connections. Where decks attach to the house, wind-driven rain exploits the flashing joint.
The Most Vulnerable Spots
| Area | Why It Is Vulnerable |
|---|---|
| Windward-facing walls | Take the full pressure of storm winds head-on |
| Window and door trim | Multiple material joints, all flexing differently |
| Roof-to-wall transitions | Flashing joints under wind uplift stress |
| Gable-end vents | Large openings directly exposed to wind pressure |
| Exhaust vents and penetrations | Openings designed for air can admit water under pressure |
Pro tip: after a windstorm, check the windward side of your home first. That is where wind-driven rain does its work, even if the rest of the house looks fine.
Prevention Strategies
- Seal window and door perimeters. Maintain flexible exterior sealant at every frame-to-wall joint.
- Keep siding in good repair. Replace cracked boards and make sure the water-resistive barrier behind siding is intact.
- Upgrade vent covers. Wind-resistant vent hoods reduce water admission without blocking airflow.
- Maintain roof edge flashing. Drip edge and rake flashing are the first defense against wind-lifted shingles.
- Direct water away. Gutters, downspouts, and grading keep walls from sitting in splash-back zones.
Testing for Wind-Driven Rain Leaks
The best test is a controlled water test with a garden hose, working from the bottom of a suspect area upward while a helper watches inside with a flashlight. A moisture intrusion inspection uses calibrated spray testing plus thermal imaging to document exactly where water enters, which matters when prioritizing repairs or supporting an insurance claim.
Repairing the Damage
Repair has two parts: stopping the water and fixing what it damaged. Stopping it usually means resealing joints, replacing failed flashing, or correcting drainage. Then address the interior, dried and disinfected wall cavities, replaced insulation, and repaired drywall. For flashing-specific repairs, see our roof flashing detection guide, and after any major storm, run through our post-storm plumbing checks.
Building Envelope Basics for Homeowners
Your home's building envelope is the complete barrier between indoors and outdoors: siding, house wrap, windows, doors, roofing, and all the flashing and sealant tying them together. Wind-driven rain tests this envelope under pressure, finding every weak joint. The key concept is drainage: a well-built wall assumes some water will get past the siding, so it provides a drainage plane, usually house wrap, and a way for water to exit at the bottom. When you inspect your home, you are really checking this system. Failed sealant, missing flashing, and siding installed tight against trim all defeat the drainage design and let wind-driven rain reach the sheathing.
Landscaping and Drainage Defenses
What happens outside your walls matters as much as the walls themselves. Grade the soil so it slopes away from the foundation, with several inches of fall over the first several feet. Keep mulch and soil below the siding line; buried siding wicks water straight into the wall. Extend downspouts well away from the house so roof runoff does not splash back against windward walls. Trim shrubs so air circulates against the siding and walls dry between storms. These landscape defenses reduce the water load on your envelope, so wind-driven rain has less to work with when the next storm hits.
Finally, remember that wind-driven rain protection is cumulative. No single fix makes a home stormproof, but sealed joints, sound flashing, clear drainage, and smart landscaping work together as a system. Homes that get this layered defense stay dry through the worst Pacific storms, while homes relying on caulk alone keep leaking. Inspect annually, fix promptly, and enjoy the peace of mind.
Window and Door Weatherproofing Details
Windows and doors are the most common entry points for wind-driven rain, and the details matter. The exterior sealant joint between the frame and the siding should be continuous and flexible; cracked or missing sealant is an open invitation. Above every window and door, proper head flashing diverts water running down the wall away from the opening. Sill pans or sloped sills under the unit drain any water that does get in back to the exterior. Inside, check for staining on the drywall beneath sills after windstorms, which is the telltale sign of a failed perimeter seal. Resealing and correcting flashing at these openings stops most wind-driven rain complaints.
Wind-driven rain intrusion is predictable once you know where to look. Seal the joints, maintain the envelope, and test the windward walls before storm season. If water is getting in during storms and you cannot find the source, ProLine Leak Fix Pros will trace it for you. Call (425) 380-0028.
