EIFSFACTS.ORG

The Real Facts About EIFS  

- The Effects of Pressure Differentials -

Our research, along with that of attornies and experts looking into the EIFS problems, have finally pointed to what we believe is one of the most fundamental problems with barrier EIFS (aside from the fact that it fails to deal with water intrusion). It fails to take into account pressure differentials between the outside air and the air inside the wall cavity the system creates. The result is that large amounts of water can be forced, or "pumped" through very small openings in the system. This explains why significant damage has been found from water getting in through openings as small as a pin hole. Figure 1 shows a detail of a small opening in a caulk joint observed in a local home. Substantial water intrusion occurred in the typical "A" pattern centered immediatly below this opening, indicating that the opening was the source of penetration. A U.S. dime is shown for scale-reference.

Figure 1: Small Opening In Caulk Joint

How does this happen? As discussed elsewhere on this site, barrier EIFS is a face-sealed barrier system. That is, it is a wall system that depends on being totally sealed and water and airtight in its entirety. The application of a face-sealed system creates an air cavity between the sheathing and/or interior walls of the home and the face of the system (EIFS in this case). The problem is that when the air pressure changes on the outside a pressure differential is created between the outside air and the air in the cavity. The most common source of pressure changes is wind blowing against the face of the wall. When this happens, there is a pressure increase on the outside of the EIFS compared with the pressure in the wall cavity. Air will then be forced through any opening in the wall, no matter how small. If the face of the wall is wet, such as in a rainstorm, the air will drive water from the face of the wall into the wall cavity. Current research indicates that this mechanism is responsible for the majority of the water intrusion in face-sealed systems. Traditional wall systems (brick, block, siding, shingle, etc.) are "open" by design and balance out the pressure differentials almost instantly. They form what is known as an "open rain-screen". The irony, at least to the layperson, is that by being open they are good at preventing water from being driven through the exterior wall. As discussed elsewhere on this site, they also drain away any water that does get through.

The treatise on the subject of pressure differentials in wall structures and its effect on rain penetration was published in April, 1963 by G.K. Garden and is titled Rain Penetration and its Control. Excerpts from this work are included later on this page for those wishing to know more of the details. Suffice it to say that EIFS manufacturers totally ignored this basic principal of physics in the design of their systems. They have, recently, however, begun to address the issue as demonstrated in the advertisement for a new "Pressure Equalized" EIFS system manufactured by Dryvit Systems, Inc. as run in many building and architecture trade publications:

"Pressure equalization technology...harnessing the laws of physics".

"I was worried about air pressure differentials causing water intrusion. The vented compartmentalization/pressure equalization component of the INFINITY system alleviated those concerns".

Steve Lin, Architect

"When the wind blows, a building can experience pressure differences between the cavity and exterior walls. Building diagnostic experts acknowledge that the problem of water infiltration is primarily a function of these pressure differentials. Using pressure equalized and rain-screen technology, the INFINITY system eliminates the potential for water infiltration by neutralizing the difference between the applied wind pressure (outside) and the cavity pressure... The more rapidly this pressure is equalized through the wall, the more effective the system is in keeping water out".

So, after ignoring basic physical laws that have been utilized in traditional wall systems for hundreds of years, they now announce to the world that they have "harnessed the laws of physics". Typical.

Sto has also introduced their version of a pressure-equalized system, Sto RainScreen. Read the work by G. K. Garden that follows and you'll know where they got the name.

From Rain Penetration and its Control, April 1963 by G. K. Garden:

"Rain penetration of building walls occurs all too frequently despite advances in building technology. Although a number of traditional wall systems have had a measure of success, it is only recently that scientific studies have been undertaken to explain the mechanisms of rain penetration. Through better understanding of these mechanisms it should be possible to design and construct walls from which the problem is virtually eliminated...

Rain penetration results from a combination of water on a wall, openings to permit its passage and forces to drive or draw it inwards. It can be prevented by eliminating any one of these three conditions.

Water blown against a windward wall and thrown by air turbulence onto side walls produces an accumulation of water on the building exterior...

Depending upon the absorptivity and moisture storage capacity of surface materials and upon the rate of rainfall, a substantial film of water can form and flow on a wall face...

Openings that permit the passage of water are quite numerous on the face of a building in the form of pores, cracks, poorly bonded interfaces and joints between elements or materials. Very small pores and cracks can be covered with impermeable or semi-impermeable coatings or treated with surface waterproofing compounds, but these treatments are less likely to be effective for larger pores and cracks. Joints between elements or materials can be sealed with gaskets or sealants. If they are located where they can be wetted by rain, however, the seal must be perfect, and this is difficult to achieve because of fabrication or job site inaccuracies. Even more difficult is the maintenace of a perfect joint over a reasonable period of time, because aging of the sealant, and because differential movements between the elements constantly flex and stress the joint material. Skill and new sealing materials can all be employed, but it is seldom possible to guarantee that no openings will develop to permit the passage of water.

Even when water is available and an opening exists, leakage will not occur unless a force or combination of forces is available to move the water through the opening. The forces contributing to rain penetration are kinetic energy of the rain drop, capillary suction, gravity and air pressure differences...

A pressure drop through a wall is produced by wind pressure on the face of a building. At a point where a high rate of inward air flow occurs as a result of an opening and an air pressure drop, water can be dragged along the walls of the opening and cause rain penetration. A relatively low velocity air flow can also carry fine water droplets or snow into the wall to create the same problem. Water can be raised a considerable distance and caused to flow into a wall when an air pressure difference is added to capillary suction. An even more serious situation can occur when, as a result of a large amount of water at the surface, openings up to 3/8 inch or more are bridged with water, which is readily forced through the passage by even small differences in air pressure.

As with capillary suction and gravity, water entry resulting from an air pressure difference can be controlled by the introduction of an air space in the joint of a wall; but the air pressure in the space must always be equal to that on the wall face. This can be accomplished by providing sufficient free area of opening to the exterior to allow the wind pressure to maintain equalization. When the air pressures both outside and inside a wetted plane are equal, there is no air pressure difference to move the water inward. It is important to note that the infiltration air barrier of the building must be located inward of this air space. The air barrier, regardless of its position, is the point at which the air pressure difference between outside and inside the building occurs and must resist wind loads. Provided the air barrier does not get wet, minor air leakage through it will not be accompanied by rain penetration.

It is not conceivable that a building designer can prevent the exterior surface of a wall from getting wet nor that he can guarantee that no openings will develop to permit the passage of water. It has, however been shown that through-wall penetration of rain can be prevented by incorporating an air chamber into the joint or wall where the air pressure is always equal to that on the outside. In essance the outer layer is then an "open rain screen" that prevents wetting of the actual wall or air barrier of the building. The success of the traditional walls shown in Figure 2 is explained by this principle. Partial rain penetration or the wetting of the rain screen materials can be minimized by reducing the surface porosity and absorptivity or by control of the forces necessary to produce it. It should be emphasized that the open rain screen principle of rain penetration control can be employed for any situation where rain penetration of walls and wall components can occur, especially at joints between prefabricated components.

Figure 2 Shows Cross Sections of Shingled Wall, Cavity Brick and Brick Veneer

The advantages inherent in designs based on the open rain screen principle go far beyond those associated with rain penetration control. Movements and minor imperfections of the joint seal between pre-fabricated components become less critical, and the life of sealants is extended by shading from solar radiation. Although there may be problems regarding adequate ties and support of the rain screen when this principle is applied to the total wall covering, it should be noted that the exterior cladding is relieved of much of the normal wind load. It must be resisted by the remainder of the wall. A complete rain screen approach can result in easy handling of cladding movements and cracks after construction, and in reduced air conditioning loads, and permits rapid drying of cladding material. It also permits the better positioning of insulation and minimizes the risk of condensation within the wall. With the many advantages of the open rain screen, its full development should be pursued by all building designers.

"I had read your Web site about the pressure differential stuff and I was critical about it. And then, today, I was on the back of this house, and had just pulled the probe out. A little ball of EPS [foam-board material] was pulled out by one of the probe tips and was clinging to the EIFS [styrofoam usually clings to surfaces due to static charge]. Then, a gust of wind blew up, against the wall, and that piece of EPS was sucked right back into the hole. It hit me, right then, that it [pressure differential-driven water intrusion] is true".

Carl Schneider, Local EIFS Inspector, Conversation with NOVASHOC Founder, 14 April, 1999