What Happens Behind the Siding | Michigan Housewrap & Flashing
Most homeowners in Southeast Michigan never think about what's behind their siding—until water damage shows up in the walls. By then, the repair bill can run into the thousands. Here's the truth we've learned after 35+ years installing house siding in Detroit and across Macomb, Oakland, and St. Clair counties: the siding you see is only half the story. The real protection happens in the layers you never see—the housewrap and flashing that keep Michigan's weather from destroying your home from the inside out.
We've torn off thousands of square feet of siding over the decades, and we can tell within minutes whether the original contractor did the job right. When we find missing housewrap, improperly lapped seams, or zero flashing around windows, we know we're about to find rot, mold, and compromised sheathing. It's not dramatic—it's just physics. Water finds a way in, and without the right barriers, it stays there.
This isn't about upselling or adding unnecessary steps. This is about building science, Michigan building codes, and what actually happens when freeze-thaw cycles meet a house that wasn't protected correctly. If you're considering new siding, or if you're wondering why your energy bills keep climbing despite a recent exterior upgrade, understanding what happens behind the siding is critical.
The Two-Layer Defense System: Housewrap and Flashing
Siding is your home's first line of defense against rain, snow, and wind. But it's not waterproof—and it's not supposed to be. Siding is designed to shed most of the water, but some will always get past it. That's where housewrap and flashing come in. Together, they form a secondary drainage plane that directs water down and out, away from the wood sheathing and framing.
What Housewrap Actually Does
Housewrap—brands like Tyvek, Typar, or similar weather-resistant barriers—is a breathable membrane that wraps around your home's sheathing before the siding goes on. It has two jobs:
- Block liquid water: Rain that gets behind the siding hits the housewrap and drains down to the bottom of the wall, where it exits through weep holes or at the foundation line.
- Allow water vapor to escape: Moisture from inside your home (cooking, showers, breathing) needs to escape through the wall assembly. Housewrap lets vapor pass through while blocking liquid water—preventing trapped moisture that leads to mold and rot.
Without housewrap, water that gets past your siding soaks directly into the OSB or plywood sheathing. In Michigan's climate, that moisture freezes, thaws, and repeats—accelerating wood decay and creating an environment where mold thrives. We've seen homes in Sterling Heights and Rochester Hills where missing or improperly installed housewrap led to complete sheathing replacement within 10 years of a siding job.
What Flashing Does (and Where It Goes)
Flashing is thin metal or adhesive membrane material installed at vulnerable points—anywhere water is likely to penetrate. The most critical spots:
- Window and door heads: A properly installed head flashing (or drip cap) directs water out and over the window, not into the gap between the window frame and the rough opening.
- Window sills: Sill flashing creates a pan that catches any water that gets past the window and drains it to the exterior.
- Corners: Inside and outside corners are transition points where siding panels meet—without flashing, water can wick into the seam.
- Horizontal seams: Any place where siding panels butt together horizontally (like on tall walls) needs flashing to prevent water from running behind the joint.
Flashing isn't optional—it's required by the International Residential Code (IRC) and Michigan building codes. But enforcement varies, and not every contractor follows the rules. When we provide exterior services in Detroit and surrounding areas, flashing installation is non-negotiable. It's part of doing the job right the first time.
Why Michigan Weather Makes This Critical
If you lived in Arizona or Southern California, you could probably get away with shortcuts. But Michigan's climate is uniquely hard on buildings. We deal with:
- Freeze-thaw cycles: Water that gets into cracks or behind siding freezes, expands, and breaks apart materials. This happens dozens of times each winter across Southeast Michigan.
- Lake-effect snow and ice: Heavy snow loads and ice dams on roofs create meltwater that runs down walls. If your Detroit roofing services didn't address attic ventilation and insulation, that meltwater becomes a year-round problem.
- High humidity in summer: Michigan summers are humid. Without proper vapor permeability in your wall assembly, moisture gets trapped and condenses inside the wall cavity.
- Wind-driven rain: Storms off Lake St. Clair and Lake Huron drive rain horizontally into siding. Without a drainage plane, that water has nowhere to go but into your walls.
We've worked on homes in Grosse Pointe Farms and Lake Orion where the original siding installation looked fine from the street—until we pulled it off and found black mold on the sheathing and soaking-wet fiberglass insulation. The contractor had skipped the housewrap entirely, assuming the vinyl siding would be enough. It wasn't.
Real Example: In 2024, we replaced siding on a 1970s ranch in Clinton Township. The original contractor had installed vinyl siding directly over the old wood siding with no housewrap. After 15 years, the homeowner noticed soft spots near the windows. When we opened the wall, the OSB sheathing was crumbling, and the wall studs had visible rot. Total repair cost: $18,000. Proper housewrap and flashing would have prevented all of it.
What Proper Flashing Looks Like (and Why It Matters)
Flashing installation follows a specific sequence—it's not just slapping metal around a window and calling it done. Here's how we do it on every siding installation in Southeast Michigan:
Window Flashing Sequence
- Sill flashing first: We install a flexible membrane (like Vycor or similar) that wraps up the sides of the rough opening and creates a sloped pan that drains to the exterior.
- Jamb flashing: Side flashing overlaps the sill flashing and extends above the window head.
- Head flashing last: The top flashing overlaps the jamb flashing and the housewrap above, creating a shingling effect—each layer sheds water onto the layer below.
This sequence ensures water always drains outward. If you reverse the order—say, install the head flashing before the jamb flashing—water can run behind the flashing and into the wall. It's a small detail that makes a huge difference over 20 years.
Corner and Trim Flashing
Outside corners are especially vulnerable because two siding planes meet at a 90-degree angle. We install metal corner flashing or adhesive membrane behind the corner trim before the siding goes on. Inside corners get similar treatment—any place where water can collect or wick into a joint gets flashed.
For homes getting James Hardie fiber cement siding or LP SmartSide engineered wood, flashing is even more critical. These products are more rigid than vinyl and don't flex to accommodate water intrusion. If water gets behind them and can't drain, the substrate rots quickly.
Integration with Windows
If you're also replacing windows, the flashing and housewrap integration becomes even more important. We coordinate our Detroit window experts with the siding crew to ensure the window flange sits on top of the housewrap and the head flashing laps over the window flange. This creates a continuous drainage plane from the top of the wall to the bottom.
Poorly coordinated window and siding jobs—where the trades don't talk to each other—are a common source of leaks. That's one reason we handle both in-house. Our crews know the sequence, and they follow it on every job.
Common Mistakes We Fix Every Year
After 35+ years in business and over 500 completed projects, we've seen every shortcut in the book. Here are the most common housewrap and flashing mistakes we encounter—and what they cost homeowners down the line.
1. No Housewrap at All
Believe it or not, we still find homes where the contractor installed siding directly over old siding or bare sheathing with no weather-resistant barrier. This is a code violation, but it happens—especially with unlicensed contractors or "weekend warrior" crews. The result is always the same: water damage within 5-10 years.
2. Housewrap Installed Upside Down or Backwards
Housewrap has a specific orientation—the printed side usually faces out, and the seams must overlap like shingles (upper layer over lower layer). We've seen installations where the housewrap was installed backwards, preventing proper drainage, or where seams were taped incorrectly, creating gaps for water to enter.
3. Missing or Incorrect Window Flashing
This is the most common issue we fix. Contractors either skip flashing entirely, install it in the wrong order, or use the wrong materials. We've seen duct tape used as window flashing. We've seen roofing felt instead of flexible membrane. None of it works long-term.
4. No Kickout Flashing at Roof-Wall Intersections
Where a roof meets a sidewall—common on dormers and L-shaped homes—you need kickout flashing to direct water from the roof into the seamless gutters in Detroit, MI, not behind the siding. Without it, water runs down the roof, hits the wall, and soaks into the siding. This is a leading cause of rot at roof-wall transitions.
5. Gaps in the Drainage Plane
Housewrap must be continuous—any gap is a potential entry point for water. We've seen installations where housewrap was cut around windows and never reconnected, or where the bottom edge wasn't properly lapped over the foundation flashing. These gaps let water bypass the drainage plane entirely.
Why This Happens: Most of these mistakes come down to speed and cost-cutting. Installing housewrap and flashing correctly takes time and attention to detail. Contractors who bid too low or promise impossibly fast timelines cut corners to stay on schedule. That's why we've built our reputation on doing the opposite—showing up on time, working carefully, and doing it right the first time, even if it takes an extra day.
The Cost Reality: Investment vs. Future Repair Bills
Let's talk numbers. Proper housewrap and flashing add about 10-15% to the material cost of a siding job. On a typical 2,000-square-foot home in Southeast Michigan, that's roughly $800-$1,500 in additional materials and labor. Some homeowners balk at that number—until they understand what happens without it.
What You're Paying For
- High-quality housewrap: Tyvek HomeWrap or equivalent runs about $0.30-$0.50 per square foot installed.
- Flexible flashing membrane: Products like Vycor or Zip System flashing tape cost $15-$30 per roll, and a typical home needs 3-5 rolls.
- Metal flashing: Aluminum or galvanized steel flashing for corners and trim runs $2-$5 per linear foot.
- Labor: Proper installation adds 1-2 days to a siding project, depending on complexity.
What You're Avoiding
Compare that $800-$1,500 investment to the cost of fixing water damage:
- Sheathing replacement: $3,000-$8,000 depending on how much needs to be replaced.
- Mold remediation: $2,000-$10,000 if mold has spread into wall cavities or insulation.
- Structural framing repair: $5,000-$15,000 if water damage has compromised studs, sills, or headers.
- Interior drywall and paint: $2,000-$5,000 to repair and repaint interior walls affected by water intrusion.
Total potential repair cost: $12,000-$38,000. Suddenly that $1,500 for proper housewrap and flashing looks like the bargain it is.
Energy Savings
Proper housewrap also improves energy efficiency. By blocking air infiltration and allowing moisture to escape, it keeps your insulation services in Southeast Michigan working at full capacity. Homeowners in Troy and Warren who've upgraded to new siding with proper housewrap often report 10-15% reductions in heating and cooling costs—enough to pay back the investment in 5-7 years.
Signs Your Home Has Problems Behind the Siding
How do you know if your existing siding job was done right? Here are the warning signs we look for when homeowners call us for an inspection:
Exterior Signs
- Staining or discoloration around windows: Dark streaks or water stains below windows suggest water is getting past the flashing and running down the wall.
- Peeling paint or bubbling siding: Moisture trapped behind the siding causes paint to fail or vinyl to bubble.
- Soft spots or sagging siding: If you press on the siding and it feels spongy, the sheathing behind it is probably rotted.
- Visible gaps or cracks around trim: Gaps where trim meets siding or where corners don't fit tightly suggest improper flashing or installation.
Interior Signs
- Water stains on interior walls or ceilings: Especially near windows or in corners—this is water that's traveled through the wall cavity.
- Musty odors: Mold growing inside walls has a distinctive smell, especially in basements or near exterior walls.
- Peeling interior paint or wallpaper: Moisture coming through the wall pushes paint and wallpaper off the drywall.
- High humidity or condensation on windows: If your home feels damp even with good ventilation, moisture may be entering through the walls.
When to Call a Contractor
If you see any of these signs, it's worth getting a professional inspection. At NEXT Exteriors, we offer free inspections for homeowners in Macomb, Oakland, and St. Clair counties. We'll check your siding, look for signs of water intrusion, and give you an honest assessment of what needs to be fixed—no pressure, no gimmicks.
Sometimes the fix is minor—resealing a window or replacing a small section of flashing. Other times, we find more extensive damage that requires siding replacement. Either way, catching it early saves money. Water damage compounds over time, and what starts as a $500 repair can turn into a $15,000 problem if you wait.
How NEXT Exteriors Handles Housewrap and Flashing
When you hire us for a siding project, housewrap and flashing aren't add-ons—they're part of the base scope. Here's our process:
- Remove old siding carefully: We inspect the sheathing for damage and replace any rotted sections before the new housewrap goes on.
- Install housewrap in the correct sequence: Bottom to top, with seams overlapped and taped. We use Tyvek or equivalent products with a proven track record in Michigan's climate.
- Flash every penetration: Windows, doors, vents, light fixtures—anything that breaks the plane of the wall gets flashed before siding installation.
- Coordinate with other trades: If we're also handling window replacement in Detroit, roof replacement in Metro Detroit, or exterior painting in Southeast Michigan, we sequence the work so each layer integrates correctly.
- Final inspection: Before the siding goes on, we walk the job with the crew to verify every detail. Once the siding is installed, you can't see the housewrap or flashing—so we make sure it's right before we cover it up.
This level of attention is why we've maintained a 5.0-star average rating across 87+ reviews and an A+ BBB accreditation since 2006. We're not the cheapest option in Southeast Michigan, but we're the one you won't regret hiring.
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Frequently Asked Questions
Technically yes, but it's not recommended—and it violates most building codes. Installing new siding over old siding without removing the old material and adding housewrap traps moisture between the layers. This accelerates rot and mold growth. Michigan building codes require a weather-resistant barrier (housewrap) over the sheathing. If you're investing in new siding, do it right—remove the old siding, inspect and repair the sheathing, install housewrap and flashing, then install the new siding.
Quality housewrap like Tyvek is designed to last the lifetime of the siding—typically 30-50 years when properly installed and protected by siding. The key is proper installation: seams must be overlapped and taped, and the housewrap must be covered by siding within a few months to prevent UV degradation. Housewrap left exposed to sunlight will break down in 6-12 months, so timing the siding installation is critical.
Tyvek is a brand name—it's DuPont's version of housewrap, and it's one of the most widely used products in the industry. "Housewrap" is the generic term for any weather-resistant barrier that goes over sheathing. Other brands include Typar, Barricade, and Zip System. They all do the same job: block liquid water while allowing vapor to pass through. Tyvek is popular because it's been tested extensively and has a proven track record in all climates, including Michigan's harsh freeze-thaw cycles.
Yes. Insulated siding (vinyl siding with foam backing) provides some additional thermal resistance, but it's not a weather-resistant barrier. You still need housewrap over the sheathing to manage water and vapor. The foam backing on insulated siding can actually trap moisture if there's no drainage plane behind it, making proper housewrap even more critical. Don't let a contractor tell you insulated siding eliminates the need for housewrap—it doesn't.
Incorrect flashing is one of the leading causes of water damage in homes. If flashing is installed in the wrong order (for example, head flashing under jamb flashing instead of over it), water can run behind the flashing and into the wall cavity. Over time, this causes sheathing rot, mold growth, and structural damage. The worst part: you won't know there's a problem until water stains appear on interior walls or the siding starts to sag—by then, the damage is extensive and expensive to repair.
No—once the siding is installed, housewrap and flashing are completely hidden. That's why it's critical to hire a contractor you trust and to verify the work is done correctly before the siding goes on. Reputable contractors will walk you through the process, show you photos of the housewrap and flashing installation, and answer any questions before covering it up. At NEXT Exteriors, we document every step with photos and invite homeowners to inspect the work at key stages.
Yes. All of our siding installations include a workmanship warranty that covers the entire installation—including housewrap, flashing, and siding. The specific warranty period depends on the materials used, but our standard workmanship warranty is 5 years. Additionally, manufacturers like CertainTeed, James Hardie, and LP SmartSide offer their own material warranties (often 30-50 years) when the product is installed by a certified contractor. As a CertainTeed Master Shingle Applicator and authorized installer for James Hardie and LP SmartSide, we ensure you get the full manufacturer warranty coverage.