The Finish Line: Selective Drainage
own EIFS designs and putting them into the codes as the acceptable way to do EIFS. I had to ask them: “What is your job? Are you in the product development business, or are you a regulator?” In effect they were making EIFS producers responsible for their designs, yet there was no recourse if their designs don’t work. I sense this is a dangerous situation in terms of potential liability.
Yet their thinking was not totally illogical – and their intentions seemed noble – but the result was questionable as to whether or not the walls would work in all ways, such as being practical to construct, reasonable cost-wise and not ruin the many other attributes of EIFS.
One of the concepts that came up in our lively discussion was that of the veneer wall vs. the cavity wall vs. the solid wall. I suppose that EIFS walls could be considered to be some form of ‘veneer’ construction. Most modern brick walls are veneer construction. And brick walls have a cavity between the brick and the supporting wall because they have to - with the zillions of lineal feet of mortar joints between the bricks, it is impossible to keep water from leaking in. Hence the drainage cavity is essential – and no portion of the wall will work without the cavity. It’s not that brick is bad per se – this is simply the way brick is. Brick is not like EIFS. EIFS walls work differently.
When EIFS was originally proposed to the Model Code groups several decades ago to get a product approval (now known as “evaluation reports”), one of the issues was that with EIFS, there was no secondary code-required water resistive barrier (WRB) between the EIFS and the supporting wall like there is with brick and stucco. The quick answer from the EIFS producers to that challenge was that the EIFS itself is the WRB and hence a second one is not needed. The code people accepted that, and for years barrier EIFS was the only EIFS product on the market. That all changed in the 1990s when leaky adjacent wall products caused damage to wood-framed walls, and EIFS got blamed for it. Now, when there are moisture-sensitive materials in the supporting walls, EIFS with drainage is required by code.
The requirement that the whole EIFS wall has to have drainage doesn’t make much sense to me, as the whole wall doesn’t leak. Why not concentrate on the edges - where the water might get in – and leave the rest of the wall alone? In other words, include the drainage capability only at the edge of the EIFS, and leave the rest of the wall as a barrier EIFS? I call this concept selective drainage, and it might save time and money but still address the concern about leaks.
If you’ve taken apart an EIFS wall that has had leaks – such as at a window – the damage usually extends down and sideways, but rarely extends into large blank wall areas. The exceptions to this are several, including long horizontal runs of windows – “strip windows” – which are common on commercial buildings, and long horizontal edges, such as at the top of a wall. Why not, in the case of other openings, incorporate the drainage around the opening, and leave the rest of the blank walls alone? This area around openings could be called the zone of influence, and could be handled by extending the drainage capability a few feet around the opening, and providing a direct discharge path at the nearest area of opportunity below (such as at the head of a window, stacked below).
I’ve tried to see how hard this would be to actually build, and there are problems. One is that with houses, there are so many openings that it would be easiest just to use drainage everywhere. But in cases like simple facades and blank end walls, why is the drainage needed everywhere? No doubt it would take some ciphering to develop guidelines as to where drainage is – and is not – needed.
You might be curious to know that there is an ASTM test for EIFS drainage. It’s called D2273, and is available online at ASTM’s Web site. This test actually determines the drainage efficiency of an EIFS-clad wall assembly. Efficiency is the key word. It does not tell you how much water is acceptable to be retained, nor how long until it is totally dried-out, but can be used to compare one wall’s efficiency with another. It also does not tell you if the wall is a good, viable, buildable design - it’s a tool. The method used in this laboratory test is run as follows: A slot is cut into the top of a large EIFS wall mockup. A measured amount of water is trickled in, and the change in the weight of the specimen is used to determine how much water is left behind. This test might be helpful in doing product development for EIFS wall drainage designs, but does not answer the $64,000 question: “How much is good enough?” – or “what constitutes adequate drainage?”
My mind tells me that the main trick to a leak-free wall is to engineer the perimeter to keep the water out in the first place. This design approach is sometimes called source drainage, and it is used on all manner of wall systems. It does require good flashing, good caulking, good workmanship and good adjacent wall components, but does not require that the whole wall have drainage.
Fortunately, the code people so far have restricted the requirement for full wall drainage for EIFS to wood frame buildings. However, a byproduct of the availability of drainage for EIFS is people who want to use it on all sorts of other EIFS wall designs, for which incorporating drainage is difficult, even though they are not required to do so. For example, consider how you would incorporate drainage with EIFS prefabricated panels on a commercial building.
A second area of concern in commercial EIFS is the size of the drainage cavity and its effect on fire performance. Some code people are advocating large cavities, which in a fire might allow the fire to get behind the foam. This is not a good thing, as one of the features of EIFS that makes it perform in a fire is that the foam is totally surrounded by materials that don’t burn.
A third concern relates to the effectiveness of the insulation. When there is a large cavity, air can move around behind the foam. Let us not forget that EIFS is an external form of insulation, and if you let outdoor air behind the foam, then it tends to negate the value of having the outboard insulation. This is especially true with large cavities that would drain better, but would essentially ventilate the wall system.
I think this idea of selective drainage is a concept worth looking into. It would be a great topic for some research. The first step, since the requirement for drainage is both code and market driven, would be to chat with the code people to see what they think. I suspect their response would be negative, as the requirements are already in the codes. But I have also found that if code people are part of the process of code changes, they tend to be willing to listen, and then it’s just a matter of time and money.
At the end of our conversation the code people asked me, “If you had an EIFS house, how would you do it?” My response is that since the code says I have to have drainage, I would obey they law, but I would take most of the money from the “fancy foam shapes” vanity budget, and instead put it into good windows, well-designed flashings and premium caulking.