In EIFS, water resistive barriers are a layer between the EIFS substrate and the EIFS insulation. They are most commonly used in EIFS with drainage wall assemblies. They are an additional layer within the wall cladding system and present some unique issues that are worth knowing about. Here are some of the issues.

Origins of WRBs

The use of a “back up” material to protect substrates (the wall structure) from water damage has been used since at least the 1980s. Usually, the WRBs’ materials were variations of the EIFS attachment adhesive or basecoat adhesive, applied as a separate layer on top of the substrate. Sometimes EIFS reinforcing mesh was added as well. This type of early WRB-like back up system was not the full EIFS with drainage system we know today.

The use of WRBs became widespread in the 1990s when problems surfaced on EIFS-clad buildings, particularly residences in the southeast. Substrates and framing were damaged by water intrusion and the lack of a drainage capability in traditional barrier type EIFS was blamed. The building code people and EIFS producers got together and developed requirements for WRBs for use when EIFS is applied over moisture sensitive walls such as walls using wood or gypsum sheathing, and wood studs. Moisture insensitive substrates, such as masonry, concrete and brick, did not require new regulations. Thus, for practical purposes, this new construction requirement applied mostly to wood frame homes and some light commercial wood frame structures. The code now requires WRBs and a drainage media of some type on these buildings.

When are WRBs Required or Specified?

Although they are generally only required by code on supporting walls using water sensitive materials, some EIFS contractors chose to use them anyway on commercial structures too. This EIFS with drainage takes additional materials and steps to install. Thus, such types of EIFS cost more. EIFS contractors I’ve chatted with indicate there is a 15 to 20 percent increase in the total cost.

Types of WRBs

WRBs come in two basic forms. The first is a paper, sheet or film material, such as building paper or house wrap. This type of WRB is attached to the substrate with mechanical anchors such as staples. The sheet, film or paper is overlapped shingle style.

The second is a trowel-applied or spray-applied coating. This is applied to the substrate as a liquid and bonds to the substrate. The coating is applied continuously and goes over the sheathing board joints.

WRBs as Part of an EIFS or as Separate Materials?

Most EIFS producers make liquid WRB materials. None make the sheet, paper or film type. A number of other building product manufacturers make liquid-applied WBRs. This type of WRB can be used with EIFS, as well as with other wall claddings such as stucco, panels and siding.

EIFS producers would prefer that their insulation attachment adhesive and their WRB materials be used in conjunction with their EIFS. This results in making an EIFS cladding system that is assembled with compatible materials for proven performance. Given that the EIFS contractor can obtain these non-EIFS WRBs separately from the EIFS components, it’s hard to know how much of the EIFS market uses WRBs.

Drainage Media

The term “drainage media” means the way by which the drainage cavity is created between the outside of the WRB and the backside of the EPS foam insulation. This media usually takes the form of vertical slots in the back of the foam, thick vertical stripes of attachment adhesive or some type of spacer such as plastic mesh or lath.

It’s also possible to have a WRB that is itself the drainage media. For example, paper-like materials that are corrugated can be placed over the substrate with the corrugations running vertically. The paper provides the channels for the water to drain out. These types of WRBs require the use of mechanical anchors to attach the EIFS foam insulation.

Holes Through WRBs

One might ask, “What good is the WRB if it has holes in it?”-when the EIFS is mechanically attached using screws and washers. Full-scale tests of such assemblies show that the many small fastener screw holes have little tendency to leak. Thus, in reality, the holes don’t matter.

Bonding to WRBs

The nonstructural nature of WRBs made of paper, films or sheets, makes bonding the EIFS foam insulation to them impossible. With liquid-applied WRBs, the EIFS foam insulation can be adhesively bonded to the WRB.

Cracking in WRBs

Paper, sheet and film WRBs don’t tend to crack per se but can be split if provisions are not made to allow for movement. For instance, this can occur at expansion joints and floor lines in wood frame buildings.

This issue is more pronounced for liquid-applied WRBs. This is because the WRB is continuously adhered to the substrate and must be able to bridge the sheathing joints. Wood based sheathing can shrink and expand due to changes in moisture content as well as open and close if the wall racks out of square due to wind or earthquakes. To ensure this does not happen, a full-scale mockup of a stud-and-sheathing wall is made and is bolted down to solid materials such as a floor slab. Force is then applied to the frame in the plane of the wall, forcing the assembly to go out of square. The WRB is then examined to see if it is strong and flexible enough to resist such forces.

Testing of WRBs

In order to qualify a WRB as being suitable, a number of tests are run. Foremost is the WRBs ability to shed, not absorb, water. Also important is the ability of liquid-applied EIFS foam attachment adhesives to stick to the WRB. In addition, the ability of the WRB to pass water vapor is important, so that moisture coming from indoors does not back up in the wall and cause condensation. With paper, sheet and film WRBs, this latter characteristic is not so critical as the WRBs have overlaps where the pieces come together, thereby allowing water vapor to move past the WRB, somewhat like what occurs with clapboard siding.

Who Installs WRBs?

This is an interesting question. With liquid-applied WRBs, the obvious installer is the EIFS contractor, as it is often trowel-applied. With paper, sheet and film WRBs, sometimes framers want to install the WRB. My thinking is that the WRB is part of the EIFS and not part of the framing. Thus, the EIFS contractor should install it. But this opinion of mine will not stop an occasional disagreement about who does what work.

Prefabricated EIFS Panels

Once in a while a designer or owner wants a WRB (EIFS with drainage) when using prefabricated EIFS panels. This is usually on taller commercial buildings. Installing the WRB over the sheathing is easy enough but what do you do where the panels meet? In other words, how do you maintain the continuity of the WRB so it can remain effective-at the EIFS panel caulking joints? This is especially critical because-if leaks do occur-I’ll bet they’ll be at the edge of the WRB at the panel joints. It’s hard to envision how you can work these adjacent wall elements (the panels) together. Think about how to build this-it’s a fussy mess.

What's Next?

A follow-up article to this one is in the works for a forthcoming issue. In it, I will show drawings of how common-and sometimes complex-edge conditions of WRBs are detailed. This includes areas such as openings, the bottom of walls, and expansion joints.