Bail Out: Campuses Strive for Leakproof Buildings
- By Julie Sturgeon
- May 1st, 2006
To protect its $35-million investment in two residence halls, Kent State University in Kent, OH, has gone with a continuous insulating sheathing over steel stud construction outside of its air/moisture barrier. The energy efficiency from this strategy will be nice. The ability to seal up the building envelope is priceless.
Mold is one of our biggest concerns nowadays in the campus environment, admits Carl Jay, director of Historic Preservation at Shawmut Design and Construction, a construction management firm headquartered in Boston. His role means he’s seen everything in the walls of buildings that range from just 30 years old to 150 years.
The main ingredient for mold — moisture — worms its way into the walls in one of three ways: vapor migration, air infiltration and liquid water literally finding cracks on the outside and streaming in. But while the answer lies in proper installation of windows, walls and roofs to prevent these paths, experts contend that addressing this trio starts with old-fashioned supervision rather than science.It’s really about understanding the materials you are specifying and then which trades will actually install those materials, Jay notes.Sometimes, five different trades might be involved in establishing an exterior skin, and if every person doesn’t meet a certain quality level, you could have failure. And I’ve found on many, many buildings, there is a incredible swing in the quality of work depending on whether it was an apprentice, a tradesperson, an afternoon or late Friday.
Internationally recognized authority Joseph Lstiburek, Ph.D., P.Eng., a member of ASHRAE, describes it as like working on a puzzle without having a picture on the box to go by, so you don’t know until the end of a very inefficient process that some pieces are missing while others don’t belong at all. In other words, the construction team is a big dysfunctional family.
To further compound the problem, many construction sites tackle their work sequence based on when materials are available. If windows are delivered late or special flashing is not available on time, laborers simply skip that step and push ahead with another angle. When they return to the original task days later, then they can’t use the best wrapping method for the windows to shed water, for instance. You can’t detail a system after the fact. You have to plan it out and do mock-ups with every component, he adds.
So at the very least, Jay recommends university officials assign someone — whether the site superintendent or assistant superintendent — to actually watch the daily installation process. It doesn’t hurt to add in computer modeling of the different systems to trace air infiltration and how the materials will perform in your climate and temperatures. Finally, test each stage for weaknesses.
Many of the schools like Harvard University that have a huge investment in their properties are bringing in a second opinion, and because this is such an important thing, architects are not balking at the idea of a peer review, Jay adds. It’s better to get a second set of eyes in there and talk out what the design is and what it requires.
The Toughest Challenge
Consultants confess the construction industry’s biggest problem these days lies with the vapor barrier; that interface between the exterior skin and the interframing system. True, buildings need air circulation, but that’s the HVAC system’s role. I’m sure architects don’t seek to get their fresh air requirements by having it leak in through the walls, points out Herbert Slone, president of the Ohio Building Officials Association and technical manager of Commercial Insulation for Owens Corning. That could be disastrous for buildings, especially steel stud ones.
According to Lstiburek, too many vapor barrier systems prevent not only wetting but also drying, should moisture find its way in despite best intentions. I love code recommendations. One of my favorites directs engineers to ‘put a vapor barrier on the warm side.’ Warm side when? In January or in July? he wrote in HPAC Engineering, where he is on the editorial advisory board. In the air-conditioned world, moisture flow is from the outside in. That means that a vapor barrier installed on the interior of a wall assembly is on the wrong side.
His recommendation: the kraft facing on fiberglass batt meets the code’s one perm-rating requirement. But unlike plastic-film vapor barriers, foil-faced fibrous cavity insulation and foil-backed gypsum sheathing, this kraft facing becomes vapor permeable as the RH it is exposed to goes up. So if the air conditioning creates a 50-percent humidity, you have a kraft facing of 10 to 20 perms, making this a smart vapor barrier that retards moisture in winter and lets the wall breathe in summer.
A peel-and-stick membrane like bitumen that effectively seals the entire wall, including the joints, is Slone’s first choice, but spray-applied materials that glue over gypsum work, too.
Filling in the Cracks
When Slone reads the ASHRAE energy codes, he rarely finds the word moisture referred, but it’s important to understand the nuances of what you accomplish with insulation because moisture is really at the height of everyone’s consideration when they are putting these packages in place, he assures. Proper insulation controls the temperature layers throughout the wall, and proper location of those temperature layers allow engineers to control dew point location where moisture condenses.
Most administrators are familiar with the materials on the market: fiberglass and extruded polystyrene lead the list. You can use any insulation product, but it’s critical to get it in the right assembly in the right way, Slone says.
A majority of buildings on campuses these days employ steel stud wall construction, which means the first step in the installation game is to make sure that insulation layer is continuous across the surface of all steel studs. Otherwise, you not only lose roughly 50 percent of the insulation’s R value when the steel studs create cold spots in the walls, but these exposures could lead to condensation as well.
When working with brick masonry walls, construction experts today prefer yesterday’s softer mortars that offer flexibility. For many years we went with too hard of mortar, and it caused cracking in the brick because there was no give. Jay explains. Cracks, of course, allow water to stream in, especially since brick is a porous material in the first place.
Brick veneer also needs an air cavity behind it, so today’s savvy architects draw in weep holes at the bottom to drain moisture that works its way to the inside. Unfortunately, too many workers allow those weep holes to become clogged with dropped mortar or their soda cans during construction. That’s why Slone advises crews use a geotextile protection mat to keep those holes clear. Jay tells his clients to inform the maintenance department of any drainage system they choose to avoid having a well-meaning crewmember caulk over openings a few years down the road.
Finally, an antimicrobial spray serves as a viable preventive treatment, but this action certainly shouldn’t be viewed as a weapon of first and only choice, in Slone’s opinion. The antimicrobial concept to me suggests that we’re giving up and allowing that water will get into the building, he says.
Roofs and windows follow the same principles: make sure water can’t get in by any of its three methods. Only the materials differ, Slone assures.
It’s crazy to think that a building will never leak, Jay notes. But if you detail it properly with the proper materials and proper sequence, I don’t think there’s any up charge in the end. It’s fixing a building that becomes very expensive.