Summary

• The Exterior Insulation Finish System (EIFS) incorporates an insulative sheathing that reduces the risk of interstitial condensation by raising the temperature of the wall assembly inboard of it, and reduces the potential for inward solar driven moisture issues. However, the relatively low permeability of the combined wood sheathing and EIFS results in a reduced drying potential of the assembly, so extra care must still be taken to minimize the chance of rain water leaking into the assembly by proper detailing and use of flashings and sealants. Only EIFS with an air gap manufactured as part of the insulation board or created by the adhesive (drained EIFS) should be used. This gap provides proper drainage to the exterior at all penetrations with the help of proper flashing details at the bottom of the wall. While air gap sizes vary considerably between different EIFS systems, and a gap of only 1 mm has been shown to be sufficient to provide drainage, larger gap sizes may improve the rate of drying. The use of a ventilated cavity (vent holes at both the top and bottom of the air gap) has also been shown to improve drying over a vented cavity (vent/drainage holes only at the bottom), and should be considered for wetter climates. However, some research has also shown that higher ventilation rate may also negatively impact the thermal resistance of the EIFS. In summary, please refer to manufacturer installation instructions and requirements.

Energy & Thermal Performance

• Advanced framing as defined by NBC 9.36.2.4. (1) (e.g. insulated headers, 2 stud corners, ladder blocking, and in-line framing) can potentially reduce the framing factor by 10% to 20%)
• Maximum nominal R-value of cavity insulation is typically limited to R19,20,22,24 (fiberglass batt) to R30 with medium density spray-applied insulation
• EIFS are available with a variety of insulation thicknesses from 1" to 3" or more.
• Most EIFS use a type 1 or 2 EPS insulation board. The insulation board properties provide an ideal attachment base for the lamina coatings.
• EIFS provides a continuous layer of insulation across the exterior wall thereby significantly minimizing thermal bridges and enhancing the overall effective R-value of the entire assembly.
• Due to the limited permanence of some proprietary applied weather barriers (located within the assembly as a drainage plane), keeping the wall dry through detailed flashing and rigorous air barrier applications is important.
• The exact RSI value for proprietary EIFS will vary between manufacturers. It would be advisable to obtain the EIFS manufacturers' proprietary testing data to ensure appropriate RSI values are recognized.

Exterior Moisture/Wetting

• Although the air gap between the insulative sheathing and the water resistive barrier is designed to drain any water which reaches the gap to the outside, extra care must be taken at all penetrations (windows, vents etc.) so that water does not leak into the assembly behind the WRB layer, as the drying potential of the wall from behind the WRB towards the outside is significantly reduced by the WRB composite and the EIFS.

Air Leakage Transported Moisture from Inside

• Air leakage into the wall must be managed by means of a continuous interior or exterior air barrier (preferably both), combined with proper detailing at any connection or penetrations (window openings, electrical boxes, plumbing penetrations etc.), which will also help reduce heating and air conditioning costs

Water Vapour Diffusion from Outside

• The risk of solar driven moisture problems is low due to the low moisture absorptivity of the EIFS skin and the insulative sheathing, as well as the relatively low permeability of the insulative sheathing.

Water Vapour Diffusion from Inside

• Even though the risk of interstitial condensation is low, vapour diffusion from the inside must be controlled by the installation of a vapour retarding membrane (polyethylene) on the inside behind the gypsum board.
• If polyethylene is used as an air/vapour barrier behind the gypsum board, then any drying potential towards the inside is essentially eliminated. It is recommended that if possible, the polyethylene is replaced with a vapour retarder paint, however, this may have code implications in some locations.

Ease of Construction

• Exterior wood sheathing provides both structural resistance to "racking" and a nailing substrate for cladding materials
• Insulation, weather barrier and air barrier details and materials are readily available and understood within the Canadian industry
• Constructing walls with exterior insulation is rapidly becoming common practice in some Canadian Zones
• Handling, application and process integration of rigid insulation by Suppliers and Framers can initially affect cycle time - however, production cycle times quickly return to normal after the first few built units
• Materials such as studs, wood sheathing panels and/or insulation sheet goods are readily available in pre-cut lengths for 8' and 9' wall heights
• Length of fastener may need minor adjustment to ensure proper penetration depth into framing member
• Exterior insulating sheathing can be an effective exterior air barrier when joints and seams are properly sealed with compatible air barrier qualified tapes, mastic, or caulking
• Advanced framing as defined by NBC 9.36.2.4. (1) (e.g. insulated headers, 2 stud corners, ladder blocking, and in-line framing can potentially reduce the framing factor by 10% to 20%) could be further enhanced through in-line framing wherein double top plates can be limited to single plates (this is most efficiently done by referencing the roof truss layout spacing prior to laying out the first wall assembly) . See http://www.performancewalls.org/?content=app_pf_afadvantages.
• EIFS are tested and approved as an entire system. It is critical that EIFS be applied using the referenced manufacturers' materials and application methods.
• EIFS will require water management and weather resistant barrier detailing and application. This includes preparing all intended openings with integrated flashing and drainage details.
• Length of EIFS fastener will vary with thickness of EIFS EPS insulation.
• EIFS can be an effective exterior air barrier. Most EIFS manufacturers provide specific details and cut-sheets detailing how to ensure continuity of the air barrier through openings and penetrations of the envelope.
• It is highly recommend that EIFS applications be applied as a "system" as per CCMC specifications and approvals. Mixing elements of various EIFS systems from various manufacturers is extremely risky.
• Some Municipalities may require additional inspections of EIFS systems.

Affordability: Cost Implications

• Advanced framing as defined by NBC 9.36.2.4. (1) (e.g. insulated headers, 2 stud corners, ladder blocking, and in-line framing) can potentially reduce overall lumber costs by upwards of 10 to 20% (i.e. for softwood and panel products)
• Cost of EIFS material and related labour vary widely from region to region

Esthetics: Architectural Design

• Exterior wood sheathing provides a nailing substrate for cladding materials including various siding applications (vertical or horizontal)
• Exterior wall dimension width may have minor effect on interior dimensions (i.e. stair widths on exterior walls and overall interior useable square footage)
• Wall thickness adjustment may not require minor increase of foundation wall thickness (e.g. 8" to 10" foundation width) in some applications. EIFS is non-structural cladding adhered directly to the structural wall.
• Manufacturer proprietary EIFS material coatings and integrated drainage spaces will vary in thickness and design. Therefore, it would be prudent for designers to reference the exact EIFS specifications and testing data.
• EIFS provide an array of exterior finishes that resembles stucco. EIFS and stucco are not the same. The primary difference is that in EIFS, the thermal insulating boards support the base coat with integral glass fibre reinforcing mesh. This differs from conventional stucco, where the reinforcement is the supporting element of the rendering.

Additional Sources of Information

• Designing Energy Efficient Building Enclosures, FPInnovations
  
  
  High R Value Enclosure Assemblies, Building Science Corporation
  
  
  Guide to Attaching Exterior Wall Coverings through Foam Sheathing to Wood or Steel Wall Framing, FSC
  
  
  EIFS Practice Manual by the EIFS Council of Canada