Menu

Air Leakage, Indoor Air Quality and System Durability

Posted on 5/22/2012 1:42:17 PM By Bob Braun
  

In this forth blog in the ASC Building Products series I will continue the theme set in blog #1-3: sealants and adhesives used to air seal the gaps and joints between the many installed building products used in construction.  Previously I highlighted many of the building applications for sealants and adhesives and related consensus standards.  Here I will discuss related issues around two very current and major topics: the relationship of indoor air quality and the durability of the air barrier system to effective building performance. 

As previously discussed there are literally hundreds of points of possible air leakage in buildings and very often the leakage occurs between the interface/junction of two or more materials that may or may not be the same material.  Thus the use of adhesives and sealants is essential in connecting these materials to create an air tight system.

It has often been suggested that buildings must “not be too tight” or that they “should be able to breathe.”  I attended a luncheon meeting of architects ten years ago and this was the general consensus when this issue came up.  At the time building air leakage was becoming a hot topic and many concerns existed.  Historically it was always the case by default that the many leakage paths for air infiltration or exfiltration between the various poorly connected building materials insured the inside occupants had more than sufficient “fresh air” however this also lead to decreased energy efficiency and both moisture and mold damage.  Since this time many organizations have taken a leading role in clarifying the need for outside air supply versus how that is achieved.  Commercial buildings which have been designed to provide a specific number of air changes per hour (ACH) to insure the air is healthy were also historically subject to this uncontrolled air leakage.  In recent years ASHRAE has begun to address this problem through both research efforts and the creation of standards.  The ASHRAE Standards 62.1 and 62.2 are legion in this area with the former covering high rise buildings and the latter low rise residential.  Specific ACH values are specified depending on the building area usage.  Unfortunately it is very difficult to measure all the unintended air leakage paths in a high rise where as this can easily be done in low rise buildings as shown in Blog #2.  Over the years many other organizations have helped develop the consensus for fresh air requirements and Canadian associations have been at the front.  In the US, ASTM E06 and four other Committees have standards related to indoor air quality.  In total, sixty three ASTM standards offer methods for the sampling and analysis of indoor air quality via the following groups:


  • D22.05 Indoor Air

  • E06 Performance of Buildings

  • E30 Forensic Sciences

  • E35 Pesticides, Antimicrobials, and Alternative Control Agents

  • E47 Biological Effects and Environmental Fat

Here is a link to the EPA Protocol titled, “Testing for Indoor Air Quality
Section 01 81 09”: http://www.epa.gov/rtp/campus/environmental/018109.pdf

This link leads to the Illinois Department of Public Health Guidelines for
Indoor Air Quality:
http://www.idph.state.il.us/envhealth/factsheets/indoorairqualityguide_fs.htm

The table below indicates recommended air change rates (air changes per hour) in some common types of rooms and buildings and demonstrates how values vary:

Building / Room

Air Change Rates
- n -
(1/hr)

All spaces in general

min 4

Attic spaces for cooling

12 - 15

Auditoriums

8 - 15

Bakeries

20

Banks

4 - 10

Barber Shops

6 - 10

Bars

20 - 30

Beauty Shops

6 - 10

 

Now for durability…”the bugaboo that bugs us still and begs for panacea”.  This seemingly simple property is under the auspices of Subcommittee E06.22 on Durability Performance of Building Constructions.  E06 defines Durability as follows: the capability of a building, assembly, component, product, or construction to maintain serviceability over at least a specified time”.  Depending on the user’s expectation the “specified time” can vary greatly.  In addition the manufacture’s claims are often based on testing that cannot reflect the complete spectrum of the users’ applications for the product…i.e. many different ways the same material or product can be used, joined to a dissimilar material, or even joined to the same material as a lap, butt, or T&G joint.  Thus one can see looking at the various standards that have been created, that “Durability” is really a complex property and depends not only on the product but the application and the installation process as well.

Buildings have complex wall and roof designs and both assemblies are three dimensional with many layers.  Each material must be used appropriately and for the intended applications.  If not, a normally very durable material/product can fail quickly.  Many building failures have been and are related to this issue.  Hear are a few examples specifically form our industry:  Foam sealant used where exterior UV durability is needed.  An elastomeric sealant used to fill a void in excess of its design capability for internal cure or bridging capability. An adhesive applied in either excess or insufficient quantity to connect the two substrates may reduce its durability.  Below I list several ASTM publications that explore and attempt to clarify these and many other issues further.

ASTM C1519 - 10 Standard Test Method for Evaluating Durability of Building Construction Sealants by Laboratory Accelerated Weathering Procedures

ASTM E2342 - 10 Standard Test Method for Durability Testing of Duct Sealants

Durability of Building and Construction Sealants and Adhesives - STP1453

Digital Library - Past Symposia - Durability of Building and Construction Sealants and Adhesives

Durability of Building and Construction Sealants and Adhesives: 3rd Volume - STP1514

Durability of Building and Construction Sealants and Adhesives: 2nd Edition - STP1488

Here is a link to the previously mentioned DOE sponsored Whole Building Design Guide.  It has many references and visual photos germane to durability.

sealant failure 1 

In Illustration Above, Above the Joint Movement Exceeds the Sealant Capability

sealant failure 2 

In Illustration Above, Three Sided Adhesion Causes Failure

ASTM E283 Test Chamber with Foam Sealant Test Jig per C1642

 

In Blog #5 I will begin to explore the computer modeling programs that can help designers balance the many energy related requirements in building envelope construction to achieve an energy efficient design that will also lead to long term safety, energy performance, and durability.  And, as always your thoughts and comments are welcome.



comments powered by Disqus