Flashings: an invisible barrier, but essential to the waterproofing of your home

When we talk about water infiltration in a building, most people immediately think of the roof or foundation. However, the most insidious and costly infiltrations often come from a simple, often overlooked element: the flashing .

🔍 The fundamental role of flashing

Flashing is a piece of metal, membrane or flexible material installed at the junction between two surfaces of the building (roof, walls, openings, chimneys, etc.). Its function is crucial: to direct water towards the outside and prevent any infiltration behind the cladding or into the structure .

Each opening – window, door, sill, skylight, or roof junction – should be protected by a continuous flashing system, well integrated and in accordance with the rules of the art . The Quebec Construction Code, in Chapter I – Building, clearly states this in articles 9.27.3.8 and 9.26.4.2: flashings must prevent any penetration of water into walls and structural parts .

⚠️ The consequences of poor implementation

Poorly designed, poorly sealed or omitted flashing sooner or later causes:

• repeated water infiltration behind the exterior cladding;

• wood rot (lintels, rails, support posts);

• deterioration of insulation and air/vapor barriers ;

• mold growth in walls;

• and ultimately, major structural damage .

  
  

Often, these problems remain invisible for several years, until outward signs appear: swelling of the upholstery, moisture stains, efflorescence, musty odors or degradation of interior materials. At this point, repair costs often run into the tens of thousands of dollars .

🧰 The importance of compliant implementation

To be effective, a flashing must:

1. be laid sloping outwards;

2. overlap waterproofing materials (membrane, weather shield);

3. be hermetically sealed at transition points;

4. overflow slightly from the coating to allow water to drain;

5. be installed before the flooring is laid – never afterward.

   
   

A simple error in the installation sequence – such as placing the flashing above rather than below the weather barrier membrane – completely negates its effectiveness . This is why quality control and visual inspection of flashings should always be an integral part of a building inspection or survey.

🧠 The expertise of GEQ – Bâtiment Conseil

At GEQ – Bâtiment Conseil , we regularly analyze cases of water infiltration where the origin of the problem can be traced back to a deficient installation or the total absence of flashing . Our team of building and water infiltration experts applies a scientific and rigorous methodology , combining visual inspection, hygrometric measurements, thermal camera and targeted surveys, in order to precisely locate the water entry points and determine the technical cause.

We then recommend durable fixes according to Code requirements and manufacturers' installation guides (BP, Vicwest, Tyvek, Blueskin, etc.), to ensure long-lasting waterproofing of the building envelope.

🏠 In conclusion

Flashing is an architectural detail that is often invisible... until it is missing . It represents the first line of defense against water , and therefore the best investment for the longevity of your home . Properly installed flashing means a home that remains dry, healthy and strong—year after year.