February 15, 2013

Abstract: 

This research provides simple, long term, and durable solutions when using tapes and flashing membranes in conjunction with the exterior face of rigid polymeric foam sheathing to create the drainage plane of a wall system. The knowledge gained from this research will be used in future Building America construction prototypes and well as other residential construction projects to increase the long-term moisture related durability of the enclosure, and reduce the risk of liquid water intrusion. The following are best practice and product recommendations from the interviewed contractors and homebuilders who collectively have a vast amount of experience.

Executive Summary

This guide provides information and recommendations to the following groups:

  • Insulation contractors
  • General contractors
  • Builders
  • Home remodelers
  • Mechanical contractors
  • Homeowners as a guide to the work that needs to be done

The following research was conducted by the Building Science Corporation (BSC) Building America Research Team's "Energy Efficient Housing Research Partnerships" project for Task Order No. KNDJ-1-40337-03. Guidance on Taped Insulating Sheathing Drainage Planes is Subtask 7.2 under Task 7.0 – Evaluation of Advanced Retrofit Measures and Development of Retrofit Measure Guidelines. The goal of this research is to provide durable and long-term water management solutions using exterior insulating sheathing as part of the water management system. It is possible to tape or seal the joints in insulating sheathing to create a drainage plane and even an air control layer. There exists the material durability component of the tape as well as the system durability component being the taped insulating sheathing as the drainage plane.

The following are best practice and product recommendations from the interviewed contractors and homebuilders who collectively have a vast amount of experience. Three significant items were discussed with the group which are required to make taped insulating sheathing a simple, long term, and durable drainage plane:

  1. Horizontal joints should be limited or eliminated wherever possible
  2. Where a horizontal joint exists use superior materials
  3. Frequent installation inspection and regular trade training are required to maintain proper installation

Section 5 of this measure guideline contains the detailed construction procedure for the three recommended methods to effectively seal the joints in exterior insulating sheathing to create a simple, long term, and durable drainage plane.

1 Introduction

The lowest-cost, highest performing rainwater management strategy is rigid polymeric foam sheathing with sealed joints (Lstiburek 2006, 2010). There is an existing construction challenge of sealing the joints in rigid polymeric foam sheathing in a reliable and durable manner to prevent water ingress. This research provides simple, long term, and durable solutions to the water intrusion issues that are possible by using tapes and membranes as integral portions of the drainage plane of the wall system. The knowledge gained from this research will be used in future Building America construction prototypes and well as other residential construction projects to increase the long-term moisture related durability of the enclosure, and reduce the risk of liquid water intrusion.

Sustainability is not possible without durability; if you double the life of a building and you use the same amount of resources to construct it, the building is twice as resource efficient. Therefore durability is a key component of sustainability. It seems that one thing that both the development community and the environmental community can agree on is that durability is a good thing. The lessons of durability have come principally out of failure. Engineering is an iterative process of design by failure. Buildings are constructed. Problems are experienced. Designs and processes are changed. Better buildings are constructed. The building industry is in essence a reactive industry, not a proactive industry. It can be argued that the industry continues to do things until they become intolerably bad and then the industry changes. Examining failures gives us guidance on increasing the durability of building constructions. (BSD – 144)

Taping and sealing of joints in insulating sheathing has been occurring for over two decades.  Some failures and many successes have been reported over this time frame. A survey of existing installations, installers, contractors, and builders was conducted to determine the factors of success and failure. The survey provides insight into how builders across the country make taped insulating sheathing a simple, long term, and durable drainage plane. Few details are readily available to new contractors who want to start using taped insulation sheathing or for those that want to improve their current practices.  This research aims to provide feedback and key details from field application and testing which is not available from manufacturer’s specification sheets or details.

The team members involved with this project include members from Building Science Corporation, BASF, Dow, and Dupont.

2 Decision Making Criteria

Overall, the goal of the U.S. Department of Energy's (DOE) Building America program is to “reduce home energy use by 30%-50% (compared to 2009 energy codes for new homes and pre- retrofit energy use for existing homes).”  To this end, we conduct research to “develop market- ready energy solutions that improve efficiency of new and existing homes in each U.S. climate zone, while increasing comfort, safety, and durability.”

Using exterior board foam insulation as part of a whole house retrofit package can be a very effective method to reduce heat loss through the wall system aiding in achieving the energy use reduction goals of the U.S. DOE.  Sealing the face of certain board foam insulation products can create an effective and code approved drainage plane.  Some moisture related ingress failures due to failed joints have occurred in using this system prompting the necessity to develop further recommendations to improve the durability of the system.

Cost and Performance

It is difficult to assign a cost to durability but the costs and associated issues that occur with enclosure failures resulting in moisture durability issues are very expensive. Our experience with many production homebuilders in the United States has provided us with anecdotal evidence that the costs (on average) to repair a house, have increased an order of magnitude from approximately $100 ten years ago, to approximately $1500 today, largely as a result of water management issues. Because this is an average, and some houses have no reported problems, the houses that do have problems cost significantly more than $1500. This increase in costs is also related to an order of magnitude increase in the incidences of water management issues in the last decade from poorly installed and detailed water management systems.

According to discussions during the survey of builders responsible for over 27,000 homes in 2011 the following cost related information is summarized.  Most builders found when comparing taped insulating sheathing to installing a sheet weather barrier system, both methods had approximately the same total installed cost.  The labour and material costs, when considering a whole house, were roughly the same.  The decision to choose one method over the other generally is not made based on the cost of installation. One builder has found with continued use of taped insulating sheathing as the drainage plane that a cost savings has developed. As a secondary benefit, some builders have seen an improvement in whole house airtightness as a result of using taped insulating sheathing as the drainage plane.

Risk Identification

The builder survey indicated that taped insulating sheathing as the drainage plane has little to no risk when the correct materials are used and the installation is completed in a careful manner. Careless installation or improperly selected materials may result in issues. Each builder insisted that frequent installation inspection and regular trade training are required to maintain proper installation. The methods shown in Section 5 are the best practice recommendations that minimize risk according to industry experience. Attachment A contains the ICC evaluation showing taped foam plastic insulating sheathing as a code compliant water-resistive barrier.

3 Technical Description

The following research questions will be answered by this project.

  • What materials are available for this purpose? What are the characteristics of these materials?
  • Which new materials meet the performance requirements for water management with insulating sheathing?
  • What is the experience of installers in all climates?

The performance of the taped sheathing system relies on material durability and system durability. The material durability component refers to the tape. The system durability component refers to the taped insulating sheathing as the drainage plane.  Contractors have a unique perspective on these products and systems as they have first-hand experience in the site preparation & application. They also have an opportunity to see how the materials interact and perform over short time periods (e.g. during construction) and over longer time periods (e.g. through call-backs). Several contractors have implemented their own grass roots experimental programs to assess the buildability, performance, and durability of new products and systems. There is a need for researchers and product manufacturers to work with these contractors. An important first step is to document their experience, then to apply building science in the interpretation of the testing and to participate in the development of future products and testing.

4 Recommended Best Practices

Little argument should remain in the industry over the energy efficiency based financial benefits of adding exterior insulation. Using the exterior insulation as the drainage plane, removing the necessity to install a sheet or liquid applied weather barrier is the next logical step. Field implementation and durably taping the joints in the insulation in a repeatable manner is discussed in Section 5.

To bring together the experience of the nation, six homebuilders were interviewed who represent the experience of building over 27,000 homes in 2011. Many of the recommendations from the homebuilders were in the form of recommended products or material properties (primarily adhesives).  Installation methods and design recommendations are also included.

Penetration Details

In terms of window, door, and penetration flashing methods, most of the contractors and builders agreed that these details are already available and that using the right material and maintaining trade training and supervision were all that was required for success. 

Flashings details are included in the following documents available online at www.buildingscience.com:

More details are available in these books by Building Science Press:

In addition, almost every tape or flashing product manufacturer have, or are building, their own in-house drawings which depict their recommended installation methods.

Some of the most important penetrations to properly flash and drain are windows and doors. It is crucial to the durability of an assembly to install all windows and doors in a sub-sill pan flashing.  All windows leak through their frames eventually and it is important that this water is properly directed outside the enclosure system. Figure 1 shows how the window or door is to sit in the pan flashing, Figure 2 shows three methods of creating the sub-sill pan flashing. The full process to install and flash the window is shown in Figure 3 through Figure 11.  These same details shown can be applied to a door. There are other methods and improvements to these methods that can create similar systems, but these steps should be followed at a minimum.

Figure 1. Pan Flashing to Drain Openings

Figure 2. Types of Pan Flashing

Figure 3: Step 1—Install insulating sheathing; Figure 4: Step 2—Install backdam; Figure 5: Step 3—Apply first piece of seld-adhered sill flashing; Figure 6: Step 4—Install second piece of sill flashing; Figure 7: Step 5—Install corner flashing patches; Figure 8: Step 6—Install window; Figure 9: Step 7—Install self-adhered jamb flashing; Figure 10: Step 8—Install self-adhered head flashing; Figure 11: Step 9—Termination tape top edge of head flashing

Other key details covered in more detail in the recommended documents include penetrations as well as intersections between roofs and walls. An example roof to wall detail is shown in Figure 12.

Figure 12. Roof to Wall Intersection

Insulating Sheathing Joint Requirements, Recommendations, and Tape Materials

The following are best practice and product recommendations from the interviewed contractors and homebuilders who collectively have a vast amount of experience. Three significant items were discussed with the group which are required to make taped insulating sheathing a simple, long term, and durable drainage plane:

  1. Horizontal joints should be limited or eliminated wherever possible
  2. Where a horizontal joint exists use superior materials
  3. Frequent installation inspection and regular trade training are required to maintain proper installation

Where horizontal joints cannot be avoided, it was recommended by all contractors that cheap/poor/inferior products and methods should be avoided. This includes using tapes that are not designed as sheathing tapes, using thin polyethylene as z-flashing, installing narrow tape, not following the manufacturer’s guidelines as to surface preparation etc. In their experiences, it is not worth the risk to save the few dollars to be found in buying the cheap tape materials or using short-cut methods and hoping they do not fail. . .

Download the complete report here.