Why Most Coastal Homes Fail Before the Hurricane Hits
The biggest problem with hurricanes isn’t the wind.
It’s what the wind does to the pressure inside a house and what happens when the builder didn’t account for it.
I’ve walked through homes after Hurricane Florence that looked fine from the street. The roof was on. The walls were standing. But when you opened the door, the smell hit you first. Then you saw the mold spreading across the drywall like a stain you couldn’t stop.
These homes didn’t collapse. They rotted from the inside out.
And the damage didn’t start during the storm. It started years earlier, when someone made a decision about a window or a piece of flashing without understanding the physics of what a coastal storm actually does to a building.
The Balloon Principle
Think about squeezing a balloon.
When you apply pressure to one side, the balloon expands outward in every direction where the pressure is less than what you’re applying. At some point, the balloon reaches its maximum ability to flex and breaks.
A house works the same way during a hurricane.
Wind doesn’t just blow from one direction. When it pushes against one side of a house, it creates a void on the other side that has to be filled with air. This void is what causes the pressure to switch from pushing against the house to pulling away from it.
This is negative pressure. And it’s the dominant force in coastal storm damage.
When negative pressure hits, the air inside the house needs to be replaced. The house pulls air from anywhere it can, usually through the weakest area, like the space between the flashing of a window and the wall.
With that air comes water. In several forms.
What Actually Destroys the House
Here’s what most people don’t know about storm damage.
The water that gets in during the storm isn’t what destroys a home. It’s what happens after the storm passes.
Most homes lose power. The temperature is warm. The air is packed tight with water molecules and dirt. This creates the perfect environment for mold and mildew to thrive.
Once mold starts, it spreads like cancer through the house. There’s no good way to remediate it except by stripping the house down to the studs. This becomes invasive and costly.
After Hurricane Florence hit North Carolina in 2018, state health officials issued urgent warnings about what actually destroyed homes: mold growth in buildings exposed to flooding required removal of all porous items wet for more than 48 hours. That included drywall, insulation, flooring, and structural wood elements.
Many structures appeared intact from the outside but were uninhabitable for months, requiring complete gut-jobs down to the studs.
The real damage wasn’t from wind tearing houses apart. It was from water that entered through failed building envelopes and sat without power in warm, humid conditions.
Where the Envelope Fails
Windows and doors are the weakest point in a home.
They’re designed to meet a DP rating – Design Pressure. If you were to push at the center of the glass, the DP is the pounds per square inch that a window or door can withstand before it fails.
But here’s the problem: most builders in this market spec windows rated only DP30-40 when coastal codes demand DP50 or higher. Premium coastal sites require DP65-80 to handle the aggressive suction forces at corners and upper elevations.
A window’s DP rating of 50 doesn’t mean it survives 50 mph winds. It means it withstands 50 pounds per square foot of pressure, equivalent to approximately 170+ mph sustained winds.
The failure doesn’t usually happen at the glass. It happens at the seal between the window and the wall.
Most windows are installed with a fin system that’s mechanically adhered to the adjacent walls and top wall. The fins aren’t connected at the perpendicular point where they meet at the top of the window or door. This leaves a large triangular gap at the top on both sides.
If that gap isn’t properly sealed, it’s a prime area for water to be pulled into the house.
And most builders only rely on one protective method to waterproof where the windows and doors meet the adjacent structure. When that single layer fails, water gets in.
The Flashing Detail Most Builders Get Wrong
The building envelope (the skin of a home that keeps the elements out) is made of all the layers that go together: siding material, vapor barrier, flashing, house wrap, spray foam.
Every home has a unique makeup of materials from different manufacturers that have to work together to make the envelope function correctly.
Where most builders fail is doing things the way they’ve always done them. No process. No checklist. No system to ensure that every possible penetration or gap between materials has been sealed properly.
Here’s a specific example from homes I saw after Florence:
Any door should have a pan to allow water that does penetrate a window or door to be directed out of the home. If the back of the pan isn’t high enough, the force of the wind can exceed the downward force of gravity and the wind-driven water will overflow into the house and damage the flooring.
A pan isn’t always required for a door. Most builders don’t use them to reduce costs.
But a good builder will always install a pan, unless specifically directed not to by a manufacturer, that will expel any water that gets through a door.
The other critical detail: positive laps.
A positive lap means the outer or uppermost material laps over top of the preceding material. This keeps gravity from allowing water to sit on a joint and go through the joint.
This is especially important in roofing, around windows and doors, and in flashing details. The lap has to be great enough, as specified by code and the manufacturer.
In winter, water freezes and expands in the easiest direction it can, usually in the opposite direction of gravity. If you have a horizontal lap joint and the water freezes, it can get between the materials and expand. If the lap isn’t great enough, the material can expand past the waterproofing material and into a space where you don’t want water to be.
Then that water melts. And you’ve introduced water into a place it should not be.
The Tighter Home Problem
Modern homes are built tighter than ever before.
Improvements in sheathing, spray foam insulation, and fenestration products have made houses significantly more energy efficient. But this tightness has created an unintended hurricane vulnerability.
Because houses are so much tighter, the negative pressure and wind-driven rain will be literally sucked into the house through any perforation.
With older, leakier homes, water and air could move freely about. There was no one focused place. Now, the water and air have become focused to the only place they can get through.
It’s like putting your finger over the end of a rushing hose. The increased pressure causes the water volume to reduce but forces the water much more rigorously through the reduced opening.
The concentrated wind-driven pressure from outside finds the only available penetration point and forces water through it with significantly more intensity than it would in a leakier structure.
What’s Changed in the Last Five Years
The building industry has really focused on fenestrations as one of the weak links to a building envelope.
One of the places I’ve seen the biggest advances in building products is the vapor barrier. Vapor barriers and window flashing and tapes have evolved to be more permeable. This allows air to pass through a wall but keeps moisture out. It also allows moisture from inside the house to escape.
New pan systems and installation methods have changed to improve the way I fortify a window. Window manufacturers are also changing the sill details and weep details for their products to acknowledge that, as water will still be able to penetrate, the best defense is to create a way for it to easily get back out.
But most residential builders in this market still aren’t doing this.
They’re installing windows the way they always have. Following habit, not building science.
The Installation Sequence That Matters
Before I’m standing there to install a window, I’m reviewing the specific manufacturer’s installation procedure. This includes watching videos and reading through the installation instructions from the manufacturer.
I do lunch and learns with manufacturers from all different scopes to continually educate myself on the products and the building sciences that are always evolving to improve.
Once I’m on site ready to install the windows and doors, the first thing I do is make sure I have a schedule for which window and door goes in which opening. This is important because code requires specific openings be tempered, allow for egress, and the owner or architect may have selected impact-rated windows and doors for a specific location.
Prior to preparing to install a window and door, I check all the rough opening sizes to make sure they’re right. At the same time, I’m making sure I have all the right materials necessary to install the windows and doors as required by manufacturer and best building practices.
At Gwathmey Residential Group, I have my entire team watch one window and door be installed to witness the proper installation method. In addition, I create a unique window and door checklist for the home I’m installing and each window and door is signed off by the installation team.
This creates accountability.
I recognize that this is one of the most singular places of exposure for my liability and the liability of my clients.
I set each window and door using a laser to ensure they’re plumb, level, and square and that the header heights are lined up or installed with intention.
Most builders don’t build this level of accountability into their window and door installation process.
I run the same checklist and sign-off system for flashing at roof transitions, foundation waterproofing, and structural sheathing. This checklist and walk through process catches installation errors before the wall gets closed up, when fixing them costs thousands instead of tens of thousands.
The Questions You Should Ask Before Signing
If you’re building or remodeling a coastal home, here’s what you need to ask any builder:
Do you install pans under all exterior doors?
If the answer is “only when required by code,” you’re talking to someone who builds to the minimum standard.
How do you seal the triangular gaps at the top corners of window fins?
If they don’t know what you’re talking about, they don’t understand building envelope physics.
What’s your process for ensuring positive laps in all flashing details?
If they say “we’ve always done it this way,” you’re dealing with habit, not building science.
Do you have a window and door installation checklist specific to this home?
If the answer is no, there’s no accountability system in place.
Here’s the question most builders never ask themselves before installing windows in a tight modern home: if tighter construction concentrates pressure at weak points, how do you design the envelope differently to account for that intensified force?
The truth is, you build redundancy into every vulnerable transition. You don’t rely on one seal, one flashing layer, or one installation method. You assume the outermost layer will be tested beyond its rating, and you build backup systems that catch what gets through.
You install pans even when code doesn’t require them. You seal corner gaps that most builders ignore. You use approved tapes, sealants, and flashing systems in sequence, not interchangeably. You follow the manufacturer’s installation instructions exactly, because the warranty dies the moment you improvise.
And you do this knowing that every decision you make at the rough opening stage is either protecting the client from a problem they’ll never see, or creating one they’ll discover years later when the walls are closed and the damage is already spreading.
That’s why I have installation checklists. That’s why I watch the first window go in with the crew. That’s why I do lunch-and-learns on products that have been around for decades. Because building science evolves, materials change, and the homes I’m building today are tighter and more vulnerable to concentrated pressure failures than anything I built ten years ago.
The house doesn’t fail during the hurricane. It fails on the Tuesday morning when someone installs a window without understanding what happens when the wind shifts and the pressure reverses. My job is to make sure that Tuesday never comes.