The Finish Line: Floor Line Joints
In multi-story wood frame residential construction, the various floor levels are usually constructed as a series of platforms, one at a time, on top of each other. The horizontal framing at the floor line has its grain running parallel to the ground. When the wood expands and contracts due to moisture and temperature variations and floor loads, the vertical, cross-grain changes dimensions. This is especially true if the wood is more wet than normal and shrinks as it dries. With EIFS, this shrinkage is transferred from the wood framing to the sheathing, and from there, into the EIFS. The bottom line is that more movement can be transferred through the EIFS insulation to the EIFS lamina-more than the lamina can withstand. This can result in large horizontal cracks at the floor lines.
The normal solution is to put a sealant-type expansion joint at each floor to absorb the movement. Often this hurts the aesthetics of the wall, incurs additional costs, and requires maintenance. There are ways other than sealant joints to work around this problem and this article will give you some ideas on how to deal with this condition.
A common but risky solution is not to address the issue at all and simply not install any joints. There are plenty of EIFS homes built like this that are doing fine-no cracks. There are also horror stories of large cracks causing water leaks. The water leak problem is insidious though: as leakage progresses, the water gets to the wood framing, making it wetter. With this, the wood swells, putting additional stress on the crack, resulting in an even bigger crack and even more water leakage. You can see how this situation can be self-perpetuating and result in some real damage.
A common approach to this “no-joints” dilemma is to say, “We’ll take a chance and hope it doesn’t crack, but if it does, we’ll put in the joint at that time.” In my experience, if the joints are left out and there are no cracks after a full year or two, it’ll probably stay crack free, as long as there is no settlement or other structural movement, such as high winds or earthquakes.
WHERE TO PUT THE JOINT?
When the wood framing shrinks at this area of the wall, it does so from the top downward. This is because the weight of the building is pushing down on the load-bearing stud framing and compresses the now-shorter wood. The joint thus belongs near the top of the framing, as shown in Illustration 1. To make sure the movement can actually take place without compressing and buckling the sheathing, it’s necessary to put a break in the sheathing. This can be accomplished by starting and stopping the sheathing at the joint location or by placing a horizontal saw cut through the sheathing at the joint location.
The presence of a working joint at each floor line can be masked so that no joint is visible. For instance, overlapping horizontal bands in the form of foam shapes can disguise the joint; the foam shape band slides over the lower EIFS area. An example is shown in Illustration 2. The design also gets around the problem of a sealant joint that eventually will need to be replaced.
The foam shape band can be sculpted to look attractive, such as carved stone.
Load bearing light gauge steel framing can be used in lieu of wood, thereby bypassing the shrinkage problem, since there is no grain to expand and contract. You also get a more fire- and termite-resistant wall with a metal-framed wall. Metal framing works especially well with EIFS, as the external location of the insulation isolates the conductive metal framing from the outdoors, thereby improving the overall R-value of the wall over a similar wall with cavity insulation.
When non-load bearing light gauge steel framing is used on steel or concrete commercial structures, special attention needs to be given to the floor line area but for a different reason. This is because the supporting floor structures are limber and can deflect at the outside edge. This is why slip joints are used at the top edge of the framing (at the track-stud connection), so the EIFS doesn’t get crushed if the floor slab deflects excessively.
In a manner similar to the use of foam shapes to make a decorative band, sheet metal flashings can be used at each floor line in lieu of sealant joints. A simple Z-shaped flashing, as shown in Illustration 3, acts as a slip joint while providing the needed waterproofing, without the use of sealant. Aluminum extrusions can also be used, and give a cleaner, straighter edge than sheet metal. Some people think this approach of using flashings draws even more attention to an already ugly detail and hence won’t use it.
EIFS WITH DRAINAGE
EIFS that have a water resistive barrier and a drainage cavity between the insulation and substrate have a special floor line condition that needs to be addressed. This is because this type of EIFS is mandated by code in many areas for wood frame construction, and this detail occurs all the time.
The problem with this type of detail is one of maintaining the continuity of the water resistive barrier, while still allowing for movement. With WRBs that are flexible films or sheet goods, this is not too difficult but for the more rigid trowel-applied barriers, the WRB needs to be stopped and started, and an overlapping flexible or sliding seal placed at the juncture. An example, using a Z-shaped flashing that is integrated with the WRB, is shown in Illustration 4. Also, the presence of an open joint gives an opportunity to let the drainage cavity weep to the outside rather than having water drain several stories to the very bottom of the wall.
EIFS producers take the conservative route for this condition and show floor line joints in wood frame construction as a matter of policy. They show such floor line joints in the standard construction details and also call for it in their specifications. Since the floor line joint should be used, if cracks do develop, the producer may not honor the warranty since the wall wasn’t built according to specifications.
THE FINISH LINE
This is one detail that I often see missing when I review drawings for clients. I alert the designer that EIFS producers do want a joint and they should incorporate one, but frequently, they do not install the joint. So they are taking the first option, above, of No Joints-which is risky. I would tend to use the normal, producer-recommended sealant-type joint as a matter of standard practice, and use a high quality sealant product, such as a low modulus silicone, so the joint will perform well for years without maintenance.