Designing for Continuity: Sequencing Transitions and Tie-Ins in Blindside Waterproofing
Technical Advice for Architects
Blindside waterproofing is a key part of below-grade construction. It is installed before the concrete is poured and protects the structure from water intrusion. Once installed and backfilled, it is no longer accessible. This makes proper design and coordination essential.
The performance of the waterproofing system depends on more than product selection. Transitions and tie-ins are critical. These are the points where the system connects to adjacent materials and assemblies. If these areas fail, water intrusion will occur. Repairs are costly and invasive. You only get one chance to get it right.
This guide focuses on sequencing, material compatibility, and transition detailing. The technical experts at Henry have provided it to help architects prevent failures and ensure long-term building envelope performance.
Why Sequencing Matters
As you are no doubt aware, sequencing determines when and how each system is installed. For blindside waterproofing, it affects how the membrane connects to other envelope components. These include:
- Air barriers
- Vapor retarders
- Rigid insulation
- Cladding support systems
Proper sequencing ensures that connections between materials are maintained and protected throughout the construction process. Mistakes can compromise the integrity of the waterproofing system.
Poor sequencing can create gaps or weak points. For example, installing a blindside membrane before anchoring an air barrier can cause stress or punctures. Even minor damage can compromise the system once backfilled.
Sequencing also affects material compatibility. Some adhesives or sealants may not bond across systems. Others may degrade over time when combined with incompatible primers or membranes. These issues are often hidden until leaks occur.
Architects must consider sequencing early. Coordination between trades is critical. Clear details and specifications help prevent problems on site. By identifying overlapping scopes and sequencing issues during design development, architects can reduce errors before they reach the field.
Understanding Transition Challenges
Transitions are where systems meet. These areas are complex and often the most common source of waterproofing failure. That’s because they involve multiple trades, dissimilar materials and varying installation conditions.
Substrate Differences
Blindside membranes must bond to a range of substrates. These include:
- Cast-in-place concrete
- Shotcrete
- Steel
- Wood
- CMU
Each substrate behaves differently. Some absorb moisture. Others expand or contract with temperature. Adhesion varies. Some surfaces need primers. Others require tapes or reinforcing mesh.
In addition, concrete placed against blindside membranes can vary in finish and mix. Rough or irregular surfaces may require additional treatment to ensure full contact with the membrane.
Architects must account for these differences in their details. Failing to do so can result in adhesion failure or incompatibility over time.
Mixed Manufacturer Systems
Modern building design often specifies materials from several manufacturers. These products are not always compatible. One membrane may not bond with another. A sealant may not work with a certain primer. Joint tapes may peel off.
Manufacturers usually test their own systems. They likely have not tested them with others. When combining systems, written confirmation of compatibility is a must. Relying on assumptions leads to risk.
It’s important to confirm that manufacturers have reviewed the entire transition assembly, including all accessories. Even if two products seem similar, their formulations may interact in unpredictable ways.
Trade Coordination
Transitions often fall between scopes. One trade installs the blindside membrane. Another installs the air barrier. A third places concrete.
Without clear details, trades may install systems incorrectly or leave gaps. Preconstruction meetings can help. But it starts with good design.
A gap in coordination can lead to overlapping work or missed connections. Assigning responsibility for each part of a transition during design helps ensure accountability during construction.
Design Practices That Support Seamless Transitions
Architects can help ensure successful transitions by focusing on a few key practices.
Provide Clear, Scaled Details
Standard sections are not enough. Use large-scale details that show:
- Membrane overlaps
- Termination methods
- Sealant or reinforcement use
- Material sequencing
Include isometric views where geometry is complex. Drawings should be easy for contractors to follow in the field.
Clarify which system starts and which one continues. Use callouts to show compatible products or manufacturer-approved tie-ins. Visual clarity supports proper installation.
Use Specifications to Enforce Compatibility
Specifications should define:
- Minimum overlap dimensions (typically 6–12 inches)
- Approved primers, sealants, and tapes
- Testing requirements for alternates
- Manufacturer sign-off for multi-system assemblies
Avoid vague language. Be specific about material performance and sequence.
For alternate products, require documented test results and manufacturer letters. Include language that states substitutions must not affect warranty coverage.
Review Submittals Carefully
During submittal review, confirm that:
- Products are listed as compatible
- Transitions are detailed clearly
- All accessories (primers, tapes, sealants) are included
- Proposed alternates have test data or written approvals
Where needed, require mockups or field adhesion tests.
Pay special attention to transitions at grade, where blindside waterproofing connects with above-grade systems. These areas are often overlooked and prone to failure.
Encourage Preconstruction Meetings
Bring together all relevant trades:
- Waterproofing contractor
- Air barrier installer
- Structural team
- Envelope consultant
Use the meeting to confirm sequencing, responsibilities, and inspection points.
These meetings are also a good time to walk through transition details and clarify any assumptions in the drawings. The goal is to align the team before installation begins.
Designing for Common Transition Conditions
Some transition areas present recurring challenges. These require special care.
- Vertical-to-horizontal transitions (e.g., foundation wall to slab): Allow for movement. Use reinforced wraps or cant strips.
- Below-grade to above-grade tie-ins: Detail clearly where one system ends and the next begins. Include termination bars, sealants, or flashings.
- Penetrations: All pipes, conduit, rebar, and embedded steel must be sealed. Use only manufacturer-approved methods and products.
- Seismic or control joints: These require flexible, reinforced solutions that can bridge movement without tearing.
Always include protection courses for vulnerable areas. Backfill operations can damage exposed edges. Drainage boards or rigid protection layers can help.
Designers should also account for changes in elevation or wall geometry that can complicate installation. Simple steps like staggered terminations or shelf angles can help maintain system continuity.
Supporting Long-Term Performance
Blindside waterproofing must last the life of the structure. Because it can’t be accessed once buried, failure has major consequences. Architects must design for durability, flexibility, and compatibility.
To reduce risk:
- Require compatibility documentation for mixed systems
- Specify testing for substitutes or alternates
- Maintain detailed records for each approved transition
- Coordinate closely with structural and envelope consultants
Good design minimizes the need for field improvisation. It reduces liability and helps the project meet performance goals.
Designing for Long-Term Performance
Transitions and tie-ins define the success of a blindside waterproofing system. They are small details with big consequences. Architects can’t install the membrane—but they can determine whether it works.
Through better sequencing, clearer detailing, and stricter specs, architects help ensure the system performs as intended. The result is a watertight structure that stays protected for decades.