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E(nclosure) Harmony

Material compatibility for building performance

Alan Kristy Horizontal

Enclosure is the very essence of a building, giving us shelter from the elements and providing protection for all the other components and systems that keep us safe and comfortable. Sometimes failures in this all-important building system can be obvious and even catastrophic, like water pouring through a roof or cladding crashing down on a sidewalk, but thanks to professional competence and the standard of care applied by architects and contractors, these instances are rare. More commonly, breaches in this protective envelope are small and can go undetected for years or even decades, but nonetheless can compromise the day-to-day performance or the long-term durability of the structure. Sound enclosures are fundamental to healthy, sustainable building and material compatibility is the foundation of a high-performance enclosure.

Even small rifts in the enclosure can allow enough air infiltration to impact thermal comfort, enough moisture to degrade materials, and support the growth of mold and mildew (impacting air quality). This risk is significant enough that the WELL Building standard includes an optimization (Feature 14 Air Infiltration Management) requiring envelope commissioning and air leakage testing in accordance with ASHRAE Guideline 0-2005 and the National Institute of Building Sciences (NIBS) Guideline 3. Similarly, with the increased emphasis on actual building performance with frameworks like Passive House, Living Building Challenge, and zero net energy building, breaks in the thermal and air barrier can be a significant drain on a building’s energy performance. The National Institute of Standards and Technology (NIST, 1996) estimates that 15 percent of the heating loads in commercial buildings is due to air infiltration. Finally, standards like the LEED NC v4 Materials and Resources Credit Building Life-Cycle Impact Reduction have increased awareness of embodied energy in building materials, highlighting the importance of durability. A building enclosure failure can lead to the slow but steady degradation of structural integrity, shortening the life of the building. So, what are the sources of failures that lead to these undesirable consequences?

In modern building systems, the continuity of the various sheet and liquid applied membranes that make up the horizontal and vertical air and moisture barriers of roofs and walls are the keys to enclosure performance. The integration of these membranes must be sound and functional, with components firmly bonded to each other and to the various substrates they cover. Functional defects in building enclosures are often related to material incompatibilities, which occur most frequently where several different membranes come together, or where membranes are applied over varying substrates. These incompatibilities can occur in new construction, as well as in repairs, retrofits and additions, where new waterproofing systems are tied into existing materials. Areas of concern include:

  • Lap of below grade waterproofing and air/weather barrier
  • Air/weather barrier contact with sealants
  • Interface of vertical air/weather barrier with roofing
  • Contact between waterproofing membrane and finishes
  • Waterproofing membrane adherence to substrate (e.g., sheathing, concrete, soffit, paint, soil, steel)

One common issue relates to self-adhered asphaltic waterproofing membranes in contact with incompatible materials like PVC or TPO roofing, and EPDM or uncured neoprene flashing. Plasticizers in these materials can be leached out when in contact with the asphaltic layer in the waterproofing membrane, causing it to become more liquid (especially in warmer temperatures), breaking its adhesion and creating a gap for air or water intrusion. This might occur at the junction of penthouse walls or parapets and roofing, or where below-grade waterproofing membranes lap with PVC expansion joint materials. There are felt-backed membranes and transitions available that can help mitigate this risk.   

Breaches in this protective envelope are small and can go undetected for years or even decades, but nonetheless can compromise the day-to-day performance or the long-term durability of the structure. Sound enclosures are fundamental to healthy, sustainable building and material compatibility is the foundation of a high-performance enclosure.

Another area of concern is galvanic action where dissimilar metals are close together, with a likely electrolytic bridge between them. For example, if aluminum-faced membrane flashing is in contact with a stainless steel sill pan flashing at a window opening, the least noble metal (in this case the aluminum), becomes the anode and the more noble metal (stainless steel) acts as the cathode, creating galvanic action that corrodes the aluminum, potentially compromising the membrane.

Some membrane materials are susceptible to chemical corrosion from contact with adjacent materials. For example, some common below-grade waterproofing materials are not chemical resistant and could be degraded by chemicals leaching from contaminated soil that is present near the foundation.

Avoiding these common problems requires research and attention in the selection and specification of materials, and the careful detailing of these critical enclosure interfaces. Best practices include:

  • Checking manufacturer installation requirements for substrates to ensure compatibility with expected conditions (e.g., concrete moisture level, contaminated soil), including technical guides or letters.
  • Reviewing manufacturer material compatibility tests reports, and in some cases requesting they perform compatibility tests for specific project conditions.
  • Contacting the manufacturer through a technical representative or their material R and D group to discuss detail solutions if not readily available in standard literature.
  • Whenever possible, using the same manufacturer for all accessories within an enclosure system, and checking the system manufacturer’s specifications for recommended products and product limitations.
  • If incompatible materials must be used in proximity to one another, specifying and detailing appropriate separation between the materials, such as sheet metal, sealant, tape, or plastic based on the durability and requirements for the interface.
  • Requiring performance testing of mock-ups, or actual conditions after installation, to ensure a holistic and continuous system.

Architects have the primary responsibility to specify and detail the air and moisture barriers correctly, and general contractors must then be vigilant for installation errors and unapproved substitutions by trades. These building professionals have a lot to keep track of, so bottom line, they should know when to ask for help. Manufacturers should be consulted as they have a vested interest in seeing their products used successfully. Additionally, building enclosure consultants are trained to look for material incompatibilities, and through their experience and observation (diagnosing and advising on fixes for failures), can help clients avoid making costly mistakes. Seeking harmony in enclosures is critical to sustainability, long-term building performance, and the health and comfort of occupants.


Alan Scott, FAIA, LEED Fellow, LEED AP BD+C, O+M, WELL AP, CEM, is an architect with 30 years of experience in sustainable building design. He is a senior associate with WSP in Portland, Ore. Kristy Kwong, EIT, LEED GA, ENV SP, is a building enclosures designer with WSP in Los Angeles. To learn more, visit www.wsp.com/usbuiltecolog and follow Scott on Twitter @alanscott_faia.