When preparing for a siding replacement or installation, few steps are as critical as inspecting and assessing your home’s sheathing. Sheathing serves as the structural and protective layer beneath the siding, ensuring your home stays dry, insulated, and stable. If the sheathing is compromised, even the best siding installation can fail prematurely — leading to rot, mold, energy loss, and expensive repairs down the line.
In Ottawa’s harsh climate, with freeze-thaw cycles and significant moisture exposure, conducting a proper sheathing inspection before any siding project isn’t optional — it’s essential.
What Is Sheathing and Why It Matters
Sheathing is the layer of wood, OSB (Oriented Strand Board), or plywood attached to the exterior studs of your home. It provides a nailing base for siding, adds structural rigidity, and acts as part of the wall system’s moisture barrier. According to the National Building Code of Canada, sheathing must meet specific performance standards to support cladding and resist weather loads.
In older Ottawa homes, sheathing may have deteriorated over decades, especially behind vinyl or wood siding. That’s why a thorough inspection before any siding replacement can prevent hidden damage from undermining your investment.
Step 1: Remove a Test Section of Existing Siding
Before committing to a full tear-off, remove a small section of siding from a few key areas — typically near corners, window edges, and lower wall sections where moisture intrusion is most common. This allows you to get a first glimpse of the condition underneath without fully exposing your walls.
- Check for soft spots: Press gently on the sheathing. If it flexes or feels spongy, rot or water damage may be present.
- Inspect for discoloration: Dark stains often indicate past or ongoing leaks.
- Look for insect damage: Carpenter ants or termites can compromise wood sheathing.
If your inspection reveals significant issues, a more thorough removal may be necessary. Homeowners often discover rot behind old siding during replacement projects, as outlined in this detailed siding installation guide.
Step 2: Examine for Moisture Intrusion and Rot
Sheathing rot often starts in areas where flashing or caulking failed — around windows, doors, and roof-to-wall intersections. Ottawa’s wet springs and snowy winters make these transition zones particularly vulnerable.
Key signs of sheathing damage include:
- Musty odors behind the siding, indicating hidden mold.
- Delaminating plywood or OSB that crumbles when touched.
- Dark streaks or rust on nail heads — a sign that moisture has been trapped for a while.
Proper moisture management behind cladding is essential for long-term durability. Learn more about effective moisture control strategies in this guide.
Step 3: Check Structural Integrity Around Openings
Windows and doors are common failure points. If the sheathing near these openings is compromised, water can infiltrate deep into wall cavities, leading to insulation damage and interior leaks.
When inspecting these areas:
- Probe corners with a screwdriver to test for hidden rot.
- Look for missing or improperly installed flashing, especially above windows.
- Ensure headers and framing are solid before any new siding goes on.
Upgrading the flashing and integrating it properly with your weather-resistant barrier (WRB) during the siding project will prevent future issues — something experienced siding contractors prioritize. For professional guidance on this step, consult How to Choose the Right Siding Contractor.
Step 4: Evaluate the Type and Thickness of Existing Sheathing
Many older homes in Ottawa were built with thinner plywood or non-structural fiberboard sheathing. While acceptable decades ago, these materials may no longer meet today’s building performance standards. Modern siding systems often require structural sheathing with a minimum thickness of 7/16″ to provide adequate support and nail penetration.
- OSB vs. Plywood: OSB is more affordable but less moisture-tolerant. Plywood performs better in damp climates if properly sealed.
- Fiberboard or Foam: If found, these often need upgrading to structural sheathing before siding can be installed.
Review the latest Ontario Building Code updates for specific sheathing requirements in exterior wall assemblies.
Step 5: Inspect for Air Barriers and Insulation Integration
Beneath the siding, modern wall assemblies typically include house wrap, rainscreens, and continuous insulation layers. Before installing new siding, check whether your sheathing currently integrates with:
- House wrap or WRB: Torn or missing WRB should be replaced entirely.
- Insulation boards: Ensure there are no gaps or moisture traps behind rigid insulation.
- Rainscreen gaps: A vertical gap system helps drainage and drying — critical in Ottawa’s freeze-thaw conditions.
For homeowners upgrading older walls, integrating a rainscreen can drastically improve siding performance. Rainscreen Gaps & Freeze-Thaw Protection in Ottawa provides excellent insights on this topic.
Step 6: Plan for Repairs or Replacement
If your inspection uncovers areas of rot, mold, or insufficient structural support, address these problems before the new siding goes on. Common repairs include:
- Cutting out and replacing rotten sheathing panels with new plywood or OSB.
- Adding blocking or studs behind weak sections to reinforce the wall structure.
- Re-flashing windows and doors to integrate properly with WRB layers.
- Sealing penetrations such as vents, electrical boxes, and hose bibs to prevent future leaks.
It’s often cost-effective to combine sheathing replacement with insulation upgrades to improve your home’s energy efficiency and comfort during Ottawa winters.
Step 7: Get a Professional Inspection if Needed
While handy homeowners can perform a basic check, a professional siding contractor has the tools and expertise to detect hidden damage without unnecessary demolition. Moisture meters, infrared imaging, and years of experience allow pros to identify problems before they become expensive surprises.
Working with certified local experts can ensure your siding investment lasts decades. Explore Top 10 Siding Installers in Ottawa for trusted recommendations.
Why Proper Sheathing Inspection Saves Money Long-Term
Skipping sheathing inspection may save a few hours initially, but it often leads to expensive siding failures later. Here’s why:
- Prevent Mold and Structural Decay: Replacing siding over rotten sheathing traps moisture inside your walls, accelerating decay.
- Avoid Reinstallation Costs: If siding has to be removed to fix underlying damage, labor costs double.
- Maximize Energy Efficiency: Proper sheathing and insulation help keep your home warm during Ottawa’s winters and cool in the summer.
- Enhance Curb Appeal and Value: A structurally sound wall assembly ensures your new siding looks sharp for years.
When to Schedule Sheathing Inspections in Ottawa
Ideally, sheathing inspections should happen in late spring through early fall, when conditions are dry and work crews are readily available. Scheduling early also ensures you’re not rushing repairs during peak winter, when siding work is more complex and expensive.
For more preparation tips, visit Maintenance Guide: Cleaning, Caulking, and Annual Inspections to keep your exterior walls in top shape year-round.
Final Thoughts: Don’t Overlook the Foundation Beneath Your Siding
Your siding is only as good as the sheathing underneath it. A meticulous inspection, thoughtful repairs, and proper integration with WRBs and insulation layers ensure your siding project isn’t just cosmetic — it’s a structural and energy-efficiency upgrade.
For Ottawa homeowners, where climate challenges are significant, this step is crucial for the longevity of your investment.
For professional assessments, installation, or sheathing upgrades, contact Kaloozie Comfort to schedule a consultation with trusted local experts.
