Foundation Drain Placement & Cold Joint Waterproofing Guide

The Great Drainage Debate: Beside vs On Top of Footing

Steve’s (airfix) question highlights a fundamental debate in foundation waterproofing: where exactly should the french drain be placed? His contractor’s “new way” of placing drains on top of footings contradicts traditional practice, yet both methods have merit. Let’s analyze this thoroughly, especially for Toronto’s challenging clay soils.

Traditional vs Modern Drain Placement

Traditional Method: Beside the Footing

• Drain placed at footing bottom level
• Outside the footing edge
• Maximum depth for water collection
• Industry standard for decades

“New” Method: On Top of Footing

• Drain sits directly on footing
• Addresses water pooling on footing
• Easier installation
• Growing acceptance

Expert Perspectives

Peter Yost’s Traditional View: “Locate the drain at the level of the footing. This will drain the water for the entire assembly: footing and below-grade wall.”

Natesc’s Practical Experience: “In my area I know there are guys that successfully install the drain on top of the footing… it probably doesn’t make a difference.”

Both experts have valid points based on different priorities and experiences.

Understanding the Physics

Water Movement in Clay Soils

Steve mentioned: “Our soil is very dense and clay like”

Clay Soil Characteristics:

• Extremely slow percolation
• Holds water like a sponge
• Expands when wet
• Creates “bathtub effect”

In clay soils, water movement is so slow that precise drain placement becomes less critical than ensuring adequate drainage capacity and proper backfill.

The Footing Water Problem

Why Contractors Place Drains on Top:

1. Water pools on footings - Flat surface collects water
2. Cold joint vulnerability - Water sits against weak point
3. Direct drainage - Immediate water removal
4. Installation ease - No excavation beside footing

The Logic: If water reaching the footing top has “nowhere to go,” it increases infiltration risk at the cold joint.

Cold Joint Waterproofing Challenges

Steve’s Concern:

“I’m surprised they don’t waterproof the seam between the footing and the wall”

Peter Yost’s Response: “Waterproofing the cold joint is simply tough… The only way to be certain about keeping water out of the cold joint is a waterstop”

Why Cold Joints Are Problematic

Construction Reality:

• Concrete poured at different times
• No chemical bond between pours
• Natural crack formation point
• Differential movement occurs

Waterproofing Difficulties:

• Irregular surface profile
• Difficult access angle
• Material adhesion challenges
• Movement accommodation needed

Best Practices for Cold Joint Treatment

If Waterstop Wasn’t Installed:

1. Clean joint thoroughly - Remove laitance
2. Apply flexible sealant - Not rigid materials
3. Use reinforcing fabric - Spans movement
4. Extend membrane over joint - 6” minimum
5. Consider bentonite rope - Self-healing backup

Steve’s Advantage: “Luckily I insisted on a painted on capillary break” This provides some protection even without full waterproofing.

Modern Drainage Systems

Steve’s Update:

“It is about 6” tall and about 1” thick… plastic dimple material wrapped in fabric”

This Describes a Prefab Drain System:

• Dimpled plastic core for flow
• Filter fabric prevents clogging
• High flow capacity
• Consistent performance
• Faster installation

Advantages Over Traditional Pipe:

• Won’t crush or clog
• Flexible installation
• Better surface area
• Self-cleaning design
• Long-term reliability

The Installation Steve Got

What Happened:

1. Drain installed on top of footing
2. Sprayed membrane to cold joint only
3. Cold joint not specifically treated
4. Prefab dimpled drain system used
5. Gravel backfill planned

Assessment:

While not textbook traditional, this installation can work effectively, especially given:

• Interior slab 1 foot above footing
• Capillary break in place
• Quality drainage product
• Good waterproofing application

Drainage Placement Analysis

Beside Footing - Pros:

• Captures deep groundwater
• Traditional proven method
• Maximum drainage depth
• Protects footing bottom

Beside Footing - Cons:

• Harder installation
• Can undermine footing if too close
• May miss footing-top water
• Requires careful excavation

On Top of Footing - Pros:

• Direct water removal from footing
• Easier installation
• No undermining risk
• Addresses pooling water
• Faster installation

On Top of Footing - Cons:

• Doesn’t capture deep water
• Non-traditional approach
• May seem less thorough
• Questions about code compliance

Making It Work: Key Success Factors

Regardless of Placement:

1. Proper Backfill is Critical As natesc noted: “if you backfill the trench with a foot or two of stone, the whole thing’s gonna drain either way”

Requirements:

• Clean gravel minimum 12” wide
• No fines to clog system
• Extends to grade or nearly
• Filter fabric separation from soil

2. Positive Drainage Essential

• Slope to daylight or sump
• Minimum 1% grade
• No low spots
• Clean-out access points

3. Surface Water Management

• Proper grading away from house
• Functioning gutters/downspouts
• Impermeable cap near surface
• No negative drainage

Clay Soil Specific Strategies

For Toronto’s Heavy Clay:

Enhanced Drainage Zone:

• Wider gravel envelope (18-24”)
• Vertical drainage paths
• Consider drainage mat on wall
• Extra sump pump capacity

Surface Critical:

• 6” topsoil cap over gravel
• Positive surface grading
• Extended downspouts
• Consider French drains uphill

Movement Accommodation:

• Flexible waterproofing products
• Expansion joints as needed
• Monitor for settlement
• Plan for maintenance access

Recommendations for Similar Projects

If You Haven’t Started:

Best Practice Approach:

1. Install waterstop during pour
2. Waterproof entire wall and joint
3. Place drain beside footing
4. Use quality prefab drains
5. Generous gravel envelope

If Already Started (Like Steve):

Optimize What You Have:

1. Ensure excellent backfill
2. Verify positive drainage
3. Monitor performance first year
4. Address surface water aggressively
5. Document everything

The Bottom Line

Peter Yost is Technically Correct:

Traditional beside-footing placement with full waterproofing including the cold joint represents best practice.

But Natesc’s Experience Matters:

Many successful installations place drains on footings, especially with good backfill and surface water management.

For Steve’s Situation:

The installation received, while not ideal, should perform adequately given:

• Good waterproofing to cold joint
• Capillary break protection
• High interior slab level
• Quality drainage product
• Proper backfill planned

Future Considerations

Monitor These Points:

1. Cold joint during wet seasons
2. Sump pump frequency
3. Any efflorescence inside
4. Settlement around foundation
5. Surface drainage effectiveness

If Problems Develop:

• Interior drainage backup option
• Injectable cold joint sealing
• Enhanced surface management
• Additional sump capacity
• Professional assessment

Conclusion

The debate over drain placement reflects evolving practices and regional differences. While traditional beside-footing placement remains the gold standard, on-footing placement can work effectively with proper design and installation. The key is understanding water movement principles and ensuring robust overall water management.

For clay soils particularly, the drainage system’s capacity and the quality of backfill matter more than precise drain placement. Steve’s system, though non-traditional, incorporates enough good practices to likely perform well.

Professional Resources

• Foundation Drainage Systems
• Cold Joint Waterproofing
• Clay Soil Solutions
• Exterior Waterproofing Best Practices

For expert foundation drainage design and installation in Toronto, call (437) 545-0067)