Waterproofing of foundation walls in new construction: a requirement too often poorly implemented

In new residential construction, the application of waterproofing to foundation walls is a critical step in protecting the building against moisture, water infiltration and premature deterioration of the concrete. However, in practice, this standard is frequently poorly followed , particularly regarding the application height of the membrane .

👉 The waterproofing membrane must extend up to the finished ground level (ground level).

Why does the membrane need to extend up to ground level?

The most vulnerable point of a foundation is not only underground, but also at the junction of the soil and the foundation wall . It is at this point that we observe:

• rainwater runoff;

• splashes and water pooling against the concrete;

• repeated cycles of freezing and thawing;

• capillary absorption of exposed concrete.

If the waterproofing agent stops too low:

• the concrete remains exposed to moisture;

• water penetrates by capillary action;

• moisture migrates towards the inside of the building;

• Problems with efflorescence, mold and degradation may appear in the medium and long term.

What building science demonstrates

Concrete is not waterproof. It is porous by nature . When exposed to soil moisture without continuous protection:

• it acts like a sponge;

• water is drawn upwards by capillary action;

• moisture is transmitted to interior materials (framework, insulation, gypsum).

👉 A membrane interrupted before ground level creates a major weak zone in the building envelope.

Normative requirements – what the standard requires

According to the recognized principles of the Quebec Construction Code and current practice in residential construction:

• the foundation walls must be protected against moisture from the ground;

• waterproofing must be continuous ;

• the membrane must extend up to the finished floor level , without interruption;

• Any exposed area of concrete constitutes a functional non-conformity .

The key question: who is responsible?

❓ The builder or the excavation/earthmoving contractor?

👉 The direct responsibility lies with the earthmoving (excavation) contractor.

For what ?

• It is the excavation contractor who:

  • clear the foundation walls;

  • prepares the surfaces;

  • applies or coordinates the application of the membrane;

  • controls the final height before backfilling.

    
    

• Once the backfilling has been done, it is too late to correct a membrane that has been applied too low.

⚠️ The builder has a general coordination duty, but proper execution and verification of application height are the responsibility of the earthworks contractor .

Common errors observed in expert assessments

• membrane stopped 6 to 12 inches below ground level;

• concrete left exposed "because it will be covered with grass";

• absence of verification before backfilling;

• Incorrect justification: "That's correct, the drain is in place."

👉 Foundation drainage never replaces continuous waterproofing.

Essential recommendations

1. Require that the waterproofing membrane:

   • rises to the finished floor level ;

   • so that it is visible before the backfilling.

2. Documenting with photos:

   • the actual height of the membrane;

   • the condition of the wall before backfilling.

3. Refuse the backfill as long as:

   • The membrane is not compliant.

4. If in doubt:

   • Have it checked by a building expert before work is closed.

Conclusion

👉 A waterproofing membrane stopped too low is not a detail , it is a major failure of the building envelope .

👉 The standard is clear: the membrane must go up to ground level .

👉 The earthmoving contractor is responsible for ensuring this before backfilling.

In new construction, an invisible error today becomes a costly problem tomorrow .