Preventable Storefront Failures
08:50:00 AM on 10/22/2010
In my previous posting I wrote about some common causes of curtain wall failures and how the glazier can prevent them during fabrication, assembly and installation steps. As you may have guessed, I have also been asked about other systems (please, keep the questions coming) and if there are similar issues where quick remedies could have prevented the system failures.
Storefront systems typically do not have to meet some of the performance requirements inherent to multi-story curtain wall systems. That said, there are several potential deficiencies that can lead to leaks, condensation or excessive air infiltration.
Establishing and maintaining a clear path for water evacuation is critical in flush-glazed storefronts because they use a “gutter and downspout” method of controlling water within the system. Believe it or not, the glass itself is one potential obstruction to a clear evacuation path.
- Issue One: Water has drained down the vertical glass pocket and collected on top of the lower lite of glass where it has diverted toward the interior of the framing.
- Issue Two: Over time, water that has collected on top of the lower lite of glass has caused failure of insulated lites themselves.
- Remedy: Installing water deflectors at the intermediate horizontals and positioning them so that they extend past the edge of the lower lites will maintain proper water control.
<-- Water that infiltrates a storefront system is channeled down the vertical members to the sill and can weep out from there.
Water deflectors are applied to the ends of the glass pockets and span across the ends of the glass below to force water to drop down the verticals (downspouts).
Sill flashing presents its own set of issues that can arise on a storefront installation. Over the years, I have had a number of conversations regarding the correct shimming of sill flashing, location of the seals and proper installation of end dams.
- Issue One: Water is running up over the sill flashing.
- Remedy: When installing sill flashing, it is important to raise it off the floor and to level it. Providing a step-down from the frame’s sill will help evacuate water away from the flashing, rather than allowing it to settle against it.
- Issue Two: Trapped or accumulated water in the frame has lead to leaks at the back of the sill flashing.
- Remedy: This could have been caused by improperly sealing over the joint between the flashing and the sill member, or from locating the sealant bead in the bottom corner against the back leg of the flashing reducing the dam height of the sill and leading to leaks. The sealant should be located along the top of the upturned leg of the flashing to provide the maximum possible dam height.
<-- Here you can see a cut through the sill flashing and the seam the water runs out. The water seeps out between the sill and the flashing. Note that if the installer caulks over the seam instead of under the flashing it prevents the water from exiting as designed.
- Issue Three: Water collecting on the sill flashing has penetrated the corners of the framing and entered the building.
- Remedy: Properly install end dams and seal their contact points; note it is also important to mechanically pin the end dams to the flashing with a small screw to keep them properly positioned. Also note: All fasteners that penetrate the sill flashing should be sealed over. Remember even the tightest screw can allow water to seep under the screw head and down the threads.
Here you can see how the end dams are placed under the sills and then caulked and fasten into placed. This allows the end damn to move with the sill during expansion and contraction. Note that if the installer caulks over instead of under the flashing it prevents the water from exiting as designed. Note that the flashing does not run under the door jamb, but only to the outside edge. Sealant should be run along the edges where the sill meets the door jamb and into the glass pocket creating a slope to force the water back onto the flashing -->
Connecting joints, expansion joints and splices are typical metal to metal contact points that pose an opportunity for water to work its way into the framing system.
- Issue One: Water is leaking into the framing system at the joints where horizontal framing members intersect with the verticals.
- Remedy: Because of the design of storefront systems, critical seals at these metal to metal contact points are necessary to force the water down and away from the joints. Be sure to seal properly and per the manufacturer’s installation instructions.
- Issue Two: Undue stress on the perimeter fasteners around their seals have caused leaks to occur.
- Issue Three: Excessive expansion has caused entrances adjacent to a long run of sidelites to bind and not latch properly.
- Remedy: Locating expansion joints per the manufacturer’s recommendations for said storefront system can prevent issues two and three. Be sure to check the correct installation instructions for your specific framing system.
- Issue Four: A sill flashing splice joint has been exposed to excessive amounts of water and is showing evidence of deterioration.
- Remedy: If the sill flashing is spliced too close to an intermediate vertical member, they can be exposed to excessive amounts of water. Splices should use manufacturer recommended locations and materials. Note: When using a metal splice, it is important to use bond-breaker tape where indicated to prevent three-side adhesion that can result in torn seals.
<-- The sill flashing, like all other members, will also expand and contract. For runs longer that 12’ we recommend a splice joint. To achieve this, the flashing should be installed with a 1/2” gap between the two pieces. The installer should run silicone down both edges and apply the Kawneer Xpandr® splice sleeve pre-bent so it runs up the height of the rear up-turned leg across the gap. The bottom of the splice sleeve has a temporary adhesive to hold it in place until the silicone cures permanently. Once the splice is pressed into place, silicone will ooze through the holes. The excess sealant should be tooled (wiped) off.
Note that the flashing should never be spliced directly under a vertical intermediate. The higher volume of water increases the risk of leaking through the splice into the interior of the building.
Unwanted glass movement can lead to a variety of issues. Even in markets where seismic activity is not an issue, vibrations from traffic or construction can cause the glass to “walk” into the deep pocket of the frame.
- Issue One: Glass shifting has occurred and contact with glazing gaskets has been minimized in some locations causing air and/or water leakage.
- Issue Two: Glass breakage has occurred due to extreme over-shifting and continued contact between the edge of the lite and framing members.
- Remedy: Installing side blocks as specified will prevent unwanted glass movement that can lead to either issues outline above.
<-- To install the “W” side blocks, the installer flattens it and slides it into the gap between the gap of the glass and the mullion. A putty knife is used to push it all the way into the glass pocket where it will spring back to its normal shape and prevent the glass from “walking” back into the deep pocket.
As noted before, none of these issues are outside the glazier’s control. Following the systems’ installation instructions and paying close attention to the details of each project will ensure the required performance is obtained.
Remember an ounce of prevention is worth a pound of cure.