How to Check Window Flashings for Water Ingress Yourself

Window flashings are one of the most common sources of water ingress in New Zealand homes, and a basic visual inspection is something most homeowners can do safely themselves. Catching a flashing problem early can save you thousands in remediation costs — moisture getting behind cladding is a serious issue in our climate, particularly in high-rainfall regions. Here's how to check your window flashings methodically and know when to escalate.

What Are Window Flashings and Why Do They Matter?

Window flashings are strips of waterproof material — typically aluminium, galvanised steel, or flexible membrane — installed around window frames to direct water away from the wall cavity. Under the NZ Building Code, specifically Clause E2 (External Moisture), buildings must be designed and built to prevent water from entering the structure. Poorly installed or deteriorated flashings are a leading cause of E2 failures and can lead to significant structural damage and mould growth.

Tools You'll Need

Before you start, gather the following:

• A torch (head torch is ideal)
• A garden hose with a gentle spray nozzle
• A flat-head screwdriver or probe (for gentle prodding only)
• A ladder (if checking upper-storey windows — follow safe ladder practices)
• A notepad or phone to photograph findings
• Binoculars (useful for high windows you can't safely reach)

Step 1: Start with an Interior Inspection

Begin inside the house. Look at the wall and window reveal around each window:

• Staining or discolouration on the plasterboard, timber reveal, or windowsill — even old staining suggests past leaks
• Bubbling or peeling paint on the interior wall near the window corners
• Soft or spongy plasterboard — gently press around the corners; any give could indicate moisture damage
• Mould or musty smell concentrated near a window
• Rust streaks running down from fixings or flashings visible at the reveal

Document anything suspicious with photos.

Step 2: External Visual Inspection

Move outside and examine each window carefully in good daylight:

Check the Head Flashing

The head flashing sits above the window and is the most critical. Look for:

• Gaps between the flashing and the cladding above
• Flashing that is bent, buckled, or pulling away from the wall
• Missing or cracked sealant at the junction between flashing and cladding
• Rust or corrosion on metal flashings

Check the Sill Flashing

The sill flashing sits beneath the window. It should slope outward to drain water away. Look for:

• Sealant that is cracked, shrunk, or missing entirely
• Ponding or debris collecting on the sill
• Any gap between the sill flashing and the window frame

Check the Jamb Flashings

The jamb flashings run vertically down each side. Look for:

• Gaps or separations at the corners where jamb meets head or sill flashing
• Cladding that appears to be pulling away from the window frame
• Cracked or missing sealant along the vertical edges

Step 3: The Hose Test

If you suspect a leak but can't see obvious damage, a controlled hose test can help identify the source. Have a second person inside watching the suspect area while you:

1. Start at the bottom of the window and work upward — this isolates where water first enters
2. Apply a gentle stream of water to the sill area for 2–3 minutes
3. Move to the jambs, then finally the head flashing
4. The person inside calls out the moment they see moisture appear

This method helps pinpoint whether the leak is at the sill, jamb, or head — important information for any tradesperson you bring in.

Step 4: Check the Cladding Around the Window

The condition of the cladding immediately surrounding the window matters too. Whether your home has weatherboard, fibre cement (such as James Hardie products), or plaster/stucco cladding, look for:

• Cracking or crazing in plaster cladding near window corners — a classic sign of movement and potential water entry
• Weatherboards that are cupping, swelling, or showing paint failure near windows
• Any gaps where cladding meets the window frame or flashing

BRANZ research consistently identifies window-to-wall junctions as high-risk areas, particularly in older NZ homes built before modern flashing requirements were tightened.

Common Problem Signs at a Glance

When to Call a Professional

A DIY inspection is a great first step, but there are clear situations where you should engage a qualified professional:

• Any sign of active leaking or significant staining — a licensed building inspector or LBP can assess the full extent of damage
• Plaster/monolithic cladding systems — these require specialist assessment as damage is often hidden and widespread
• You're buying or selling a property — a pre-purchase building inspection is strongly recommended
• Remediation work — replacing or repairing flashings on most cladding systems is building work; check with your local council whether a building consent is required before any repairs begin
• Mould or significant timber damage — this may involve health risks and structural assessment

You can find qualified local building inspectors and LBPs on tradedirectory.co.nz.

A Note on Safety

Always use a stable, properly footed ladder when inspecting upper-storey windows. Never lean out of windows or work on roofs without appropriate safety equipment. If in doubt, use binoculars from the ground or hire a professional.

Sources & Further Reading

• MBIE Building Performance — Clause E2 External Moisture
• BRANZ — Weathertightness Research
• Licensed Building Practitioners Register
• James Hardie NZ — Cladding Systems
• WorkSafe NZ — Ladder Safety