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EIFS & Good Practice on the use of Flashing in wall construction (03/01/98 )
Exterior Insulation and Finish Systems (EIFS) are the fastest growing residential wall cladding system in the United States. Introduced into North America in the 1970's during the oil embargo, EIFS were seen as an important cladding for energy conservation. When the energy crisis passed, the aesthetic appeal of the system kept the market for EIFS growing. Today EIFS has surpassed brick in many residential markets as the cladding system of choice.
Traditional EIFS design is known as a barrier or face-seal wall system designed to resist water penetration at the outer surface. All other wall components including windows, penetrations, and adjacent construction should be watertight, or be designed and installed to drain water to the outer surface of the EIFS. This is prudent design and construction practice for all wall claddings, including conventional and one coat stucco, brick veneer, vinyl and wood siding. While incidental moisture that may get behind EIFS dries by vapor transmission, traditional EIFS are not designed to drain running water from other locations in the wall. |
The Sto Classic EIFS is a barrier/face-seal system. As used in residential construction, it consists of EPS insulation bonded directly to wood sheathing. The adhesive must be compatible with wood-based sheathing materials. All terminations of the EIFS must be backwrapped. When the adhesive has set, usually after 24 hours (significantly less with the use of Sto's 1/2 Time family of products), the insulation is rasped to provide a uniform surface. |  |
In 1995, a local building inspector found evidence of water penetration in approximately fifty EIFS-clad homes. Initial inspections showed that while the EIFS performed properly, water intrusion may have occurred because of related construction details, such as sealant joints and flashing, resulting in damage to wood substrates, and in some cases, to wood framing. Flashings and windows, in particular, were found not to comply with minimum building code standards.
In 1998, the National Association of Home Builders (NAHB) Research Center, Inc., in cooperation with the EIFS Review Committee, published a fact sheet for home owners which states, "Water intrusion occurs because rain water can gain entry through building components such as window frames, enters behind the cladding and wets the substrate and, in some cases, the wood structural members." The most common entry points are "...windows and where a roof meets a wall." Other locations include chimneys and decks." The fact sheet shows that the damage can be repaired. (reference: NAHB Research Center, Inc., "Water Intrusion and Remediation for Wood Frame Homes with Exterior Insulation and Finish Systems (EIFS), A Question and Answer Fact Sheet for Home Owners", 1st ed., 1998)
Proper attention to critical details will greatly reduce the likelihood of water penetration in a wall cladding assembly. As identified by the NAHB Research Center, the prime locations for water entry are: window frames, where a roof meets a wall, chimneys and decks. This is true for all cladding materials. Generally, improper flashing, or a lack of flashing, is the culprit in water gaining entry behind the claddings. The schematics below show correct flashing installation in some of the more critical detail areas. |
The wall cladding should terminate above the roof, at least 2" (51mm) for EIFS. This keeps the system away from roof water runoff and allows for future roof maintenance. The step flashing should extend at least 4" (100mm) behind the EIFS. At the termination of the step flashing, the roofer should install a 'kick-out' or diverter flashing to divert water running down the roof away from the wall into the gutter. |  |
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Most building codes require a flashing at the head of the window to divert water away from the window. The head flashing should be long enough to be folded over the corner of the window to protect the miter joint of the head and jamb. The interior rough opening should be protected with a waterproof membrane, which will allow water which passes the flashing and joint to drain harmlessly to the sill pan flashing and out of the building. An interior air seal should be installed around the window between the window and the rough opening. This will restrict the movement of drafts. |
A sill pan flashing is required beneath the window to catch water which passes through or around the window frame and divert it to the outside at the window sill. The most vulnerable areas are at the corners of windows and at the joint between multiple windows.
A number of materials can be used, including traditional metal flashings, innovative membranes, and engineered flashing systems such as Sto Sill Sentry.TM
Window flashings are installed prior to installation of the window and siding materials. |  |
Flashing must be installed to isolate the deck from the cladding substrate. The detail to the right shows the deck bolted to the wall. A flashing is installed over the sheathing prior to the construction of the deck. The flashing is completed with end dams, drip flashing and a flexible membrane to seal around the fastener penetrations. There are a number of different deck attachment and flashing methods. |  |
In response to changing code requirements and a perceived need to provide redundancy in construction, many EIFS manufacturers have developed EIF systems with drainage behind the insulation in conjunction with a water-resistant layer. The two basic types from Sto are shown below:
Drainage channels are created by using insulation with grooves cut into the back. The insulation is mechanically fastened over a water-resistant layer of building paper or equivalent material. The channels must be large enough to ensure continuity between different pieces of insulation, allowing water to drain. At the bottom of the channels, a drainage track is installed to allow water to escape to the outside. The system base coat and finish are installed
in the traditional manner.
Using a drained system does not remove the requirement for proper flashing below windows and in other locations to prevent water entering the wall system. |
Drainage takes place through a medium which creates a space behind the insulation. The medium can be expanded metal lath, vinyl lath or other material which will allow water to drain freely. The drainage medium is mechanically fastened over a water-resistant layer such as building paper or similar material. The insulation can then be fastened to the drainage medium with adhesive or mechanically fastened to the supporting structure. At the bottom of the drainage medium, a drainage track allows water to drain to the outside. The EIFS is then finished in the traditional manner. |  |
Once again, using a drained system does not remove the requirement for proper flashing below windows and in other locations to prevent water entering the wall assembly.
All details and construction require communication and cooperation among sub trades and the builder/general contractor. No one trade works in isolation from the others. Home builders/general contractors are responsible for sequencing and coordinating the trades that install the components in conformance with building codes and good construction practice.
For further information on any of the above, contact your Sto Sales Representative or Sto Corp. at (800) 221-2397 or e-mail our Technical Services Department at jedgar@stocorp.com. |
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For more information on EIF Systems, visit the http://www.eima.com web site |