Triple Brick Foundation Retrofit - Advanced Waterproofing Strategies

Understanding Jason’s Complex Retrofit

Your situation represents a sophisticated retrofit combining old and new construction techniques. With a 100-year-old triple brick house, partially replaced foundation, and plans for spray foam insulation, you’re navigating multiple building science challenges. Let’s analyze your concerns systematically.

Your Current Setup

Foundation Status:

• 2 sides: New 12” poured concrete
• 1 side: Attached to neighbor (semi-detached)
• Back wall: Original brick (repointed)
• French drain with sump pump installed
• Exterior coating applied (no dimple mat)

Critical Detail:

• Joists wrapped with Blueskin before embedding
• Planning 3” spray foam (R-21)
• 2x4 stud wall planned 2” from concrete

The Embedded Joist Challenge

Understanding Blueskin Protection

Michael Maines raised a crucial point about which Blueskin product was used:

Blueskin WB Air and Moisture Barrier (likely your product):

• Vapor permeable
• Protects against liquid water
• Allows drying if moisture enters
• Good choice for embedded joists

Why This Matters: Traditional embedded joists fail because:

• Direct concrete contact
• No drying potential
• Moisture wicks into wood
• Eventual rot occurs

Your Blueskin wrap creates:

• Separation from concrete
• Drainage plane for water
• Some vapor permeability
• Protection during pour

Expert Assessment

Your approach is sound, but as Michael notes: “No system is 100% reliable.”

Your Protection Layers:

1. Blueskin wrap on joists
2. 2x4 wall supporting joists
3. Spray foam sealing assembly
4. Interior finish materials

This multi-layer approach significantly reduces risk.

The Dimple Mat Dilemma

Exterior Dimple Mat Analysis

Current Situation:

• Foundation coating only
• No dimple mat installed
• 12” thick walls
• French drain present

Expert Consensus: Michael Maines: “When it’s critically important to keep water out of basements, I include at least two water management systems.”

Your Options:

1. Trust current system
2. Excavate and add dimple mat
3. Interior water management
4. Ground gutter system

Is Your Coating Sufficient?

For 12” Walls:

• Thicker walls = more protection
• Coating provides basic defense
• French drain relieves pressure
• Risk depends on water table

Krackadile’s Code Perspective: “The international residential code specifies where you need to waterproof and where you need to dampproof.”

Most coatings are dampproofing, not true waterproofing. Your thick walls help, but don’t eliminate risk.

Interior Dimple Mat Considerations

Your Constraint: In-Slab Heating

With fresh concrete and in-slab heating, interior perimeter drainage is impossible. This eliminates traditional interior dimple mat applications.

Alternative Interior Strategies:

1. Wall-Mounted Drainage: As stamant1 suggests: “Conceivably you could mount the gutter system on the wall”

• Install before spray foam
• Direct to existing sump
• Protects against high leaks
• Doesn’t address floor seepage

2. Sacrificial Strip:

• Leave 12-24” unfinished at bottom
• Monitor for moisture
• Easy access if issues arise
• Minimal aesthetic impact

3. Smart Monitoring:

• Wireless moisture sensors
• Behind-foam placement
• Early warning system
• Peace of mind

Spray Foam Application Best Practices

Your 3” Closed-Cell Plan

Advantages:

• R-21 insulation value
• Air barrier creation
• Vapor retarder properties
• Structural enhancement

Critical Installation Details:

1. Surface Preparation:

• Ensure walls are dry
• No active leaks
• Clean surface
• Proper temperature

2. Joist Pocket Treatment:

• Spray into pockets carefully
• Maintain Blueskin integrity
• Don’t overfill
• Allow for wood movement

3. Bottom Detail:

• Stop foam 1” above floor
• Prevents wicking
• Allows inspection
• Sill plate gasket

4. Top Detail:

• Seal rim joist completely
• Fire-stop as required
• Vapor barrier continuity
• Thermal bridge prevention

Risk Assessment & Mitigation

Probability of Future Issues

Low Risk Factors:

• 12” thick walls
• Professional installation
• French drain system
• Blueskin protection

Moderate Risk Factors:

• No exterior dimple mat
• Partial brick foundation
• Age of structure
• Unknown water table

High Risk Factors:

• Embedded joists (mitigated)
• Future crack potential
• Climate change impacts
• Neighbor’s foundation

Stamant1’s Ground Gutter Solution

“Consider a ground gutter — placing a 6’ wide impervious layer under the soil”

Implementation:

• No excavation to foundation
• 2-3’ deep installation
• Slopes away from house
• Reduces surface water
• Cost-effective addition

Decision Framework

Should You Excavate for Dimple Mat?

Excavate If:

• History of water issues
• High water table
• Poor site drainage
• Peace of mind worth cost
• Planning other exterior work

Skip Excavation If:

• No current issues
• Good site drainage
• Budget constraints
• Trust current system
• Accept small risk

Michael Maines’ Two-System Rule

For critical applications, two systems provide redundancy:

1. Current: Coating + French drain
2. Recommended: Add dimple mat OR ground gutter

Alternative Solutions

1. Enhanced Monitoring

• Install moisture sensors
• Regular inspections
• Document conditions
• Early intervention

2. Interior Protection

• Moisture-resistant materials
• Elevated utilities
• Waterproof flooring
• Removable finishes

3. Exterior Improvements

• Improve grading
• Extend downspouts
• Install ground gutters
• Maintain positive drainage

4. Insurance Approach

• Accept current system
• Maintain good coverage
• Document installation
• Keep repair funds available

Expert Recommendations Synthesized

Michael Maines: Two systems for critical applications Krackadile: Consider code requirements and err on caution Stamant1: Ground gutters and moisture-resistant finishes FouldB: Interior waterproofing before foam (limited by your slab)

Consensus: Your current system is reasonable but not bulletproof

Final Recommendations

For Your Specific Situation:

1. Proceed with Current Plan Your Blueskin-wrapped joists and spray foam plan is sound

2. Add Ground Gutter System Less invasive than full excavation but adds protection

3. Install Monitoring Wireless sensors provide early warning

4. Use Resilient Materials Plan finishes that tolerate occasional moisture

5. Document Everything Photos and records for future reference

The Bottom Line

Your current system with:

• 12” concrete walls
• Exterior coating
• French drain
• Blueskin-protected joists
• Planned spray foam

Provides reasonable protection. Adding a dimple mat would be ideal but not mandatory. The ground gutter offers middle-ground protection without full excavation.

Cost-Benefit Analysis

Option	Cost	Benefit	Recommendation
Status Quo	$0	Adequate	Acceptable
Full Excavation	$15,000+	Best protection	If budget allows
Ground Gutter	$3,000	Good improvement	Recommended
Monitoring Only	$500	Early warning	Minimum

Conclusion

Your retrofit plan shows excellent understanding of building science principles. The Blueskin protection for embedded joists is particularly clever. While adding an exterior dimple mat would provide additional insurance, your current system should perform adequately with proper maintenance and monitoring.

Focus on executing your spray foam installation properly and consider the ground gutter as a cost-effective enhancement. Your 2x4 wall supporting the joists adds crucial redundancy to the Blueskin protection.

Related Resources

• Spray Foam Basement Insulation
• Dimple Mat Installation
• Foundation Retrofit Solutions
• Embedded Joist Protection

Need expert guidance for your foundation retrofit? Call (437) 545-0067 for professional assessment and solutions.