Pushing the Envelope
- By Amy Milshtein
- May 1st, 2007
Everyone talks about the weather but no one does anything about it — except your building’s envelope. This barrier between you and the outside world keeps out cold, heat, rain, and wind on normal days. During weather events like hurricanes and heavy snows it becomes a safe refuge… if it’s designed correctly. Do it wrong, however, and the elements can find their way in, along with mold, mildew, and termites. How can you make sure your envelope works like it should?
Building codes remain the first line of defense in making sure the envelope is right.The International Building Code (IBC) updates every three years, said Bill Lang, product development manager for Vistawall.But local ordinances can be hit or miss.
Blowin’ in the Wind
This means that sensitive areas, like coastal regions, may not have been protected by the most stringent guidelines. The hurricane activity in the Gulf Coast two years ago, coupled with the threat of future mega-hurricanes, has locals changing their minds. The 2006 IBC codes are being reviewed and adapted on the local level in states like Alabama, Louisiana, and Mississippi, continued Lang, but again the learning curve on impact glazing remains high and enforcement can be spotty.
Impact glazing is one of the most important issues in hurricane-prone areas where debris can be propelled at your building at 120 mph or greater. If your building is in a windblown-debris region, it must employ either impact glazing that can resist debris, or shutters. The problem with shutters is that they have to be installed right when the hurricane is coming, Lang related. Many of your staff may want to tend to their own homes and families.
Even when the weather is calm, hurricane-prone climates present other design challenges. Here in Florida it is hot and humid outside and cool and dry inside, explained Zofia Jurewicz AIA, associate, HuntonBrady Architects. That’s the opposite of other environments and can lead to design mistakes.
These mistakes can appear benign on the outset but present catastrophic results. For instance, vinyl wall covering seems like an elegant, cost-effective design solution. And it is, until you apply it to the inside of an external wall. The vinyl acts as a vapor barrier and allows mold and mildew to grow behind it, said Jurewicz. She warns that common school tools like white boards, blackboards, and tack boards produce the same effect. You can have them, she continued, just not on an exterior wall.
Termite protection is another important envelope issue in warm climates. Up north the termites freeze in the winter but down here they are a year-long problem, said Jurewicz. A proper barrier will protect your building.
Let it Snow
One place where termites are not a year-round issue is Maine. Cold, dry air are our problems, related Clif Greim, principal, Harriman Associates, who on the early April day of this interview woke up to 14 in. of fresh, wet snow. Controlling humidity, in our case the lack of humidity, is paramount, particularly when the building is housing archival documents.
Such was the case at the Edmund S. Muskie Archives. Housed at Bates College in Lewiston, ME, the senator’s archives sit in a building that itself is on the National Register of Historic Places. Controlling the inside humidity at a level acceptable for archive-quality documents often comes at the cost of the building’s external masonry. Water will start to condense in the wall, and when that water freezes the outside bricks pop out of place, explained Greim. In this case we needed to preserve both the interior humidity and the outside masonry. Using forensic architecture, Greim and his team analyzed the entire building and installed the correct levels of insulation and vapor barriers to protect both the precious exterior and the building’s delicate contents.
Other buildings don’t require the same amount of precision, but controlling humidity and temperature is still important. In these cases the interior conditions fluctuate throughout the day but at a controlled rate. Humidity can cycle between 30 to 50 percent, but it has to happen slowly, Greim continued. No more than a one- to two-percent change over a two-hour period. It’s the sharp spikes in the environment that is uncomfortable and damaging.
And how do northern buildings deal with heavy snow loads? Codes require structural analysis for snow loading, but we have to be careful about where the snow collects, said Greim. You don’t want it to work its way into the flashing. While Greim tries to avoid flat roofs, he admits that budgets sometimes demand them. The technology has advanced where we can use single-ply rubber roofing, he continued. But you have to make sure the roof sheds the snow quickly and away from the entrance.
No matter where a building is located geographically, windows remain the weak link in the envelope. Windows are also perhaps a building’s strongest assets. To meet LEED requirements people are trying to get as much daylighting as possible, said Simon Etzel, senior vice president of procurement, Konover Construction in Connecticut.
However, the wrong windows and casements can also leak valuable HVAC or let in the elements. I’ve seen projects along the coast where the glazing wasn’t rated for sustained wind and the rain was blowing though the casements, related Greim. I’ve also seen windows not rated for below-zero temperatures frost up.
Lang suggests avoiding these problems by matching the right combination of glass, sealant, framing, and substrate and then testing the whole assembly. High-performance window systems can still bring thermal efficiency and daylight to a building, he said. Even earthquake-prone areas can build with lots of glazing. We can always balance an architect’s vision with an appropriate system.
And technology even allows those windows to open. Greim is now working on a project with controlled, operable windows. Sensors test outside conditions and — if they are favorable — half of the window opens, he explains. As CO2 increases, the other half opens. If the CO2 continues to rise mechanicals kick in to supplement the windows.
While operable windows are not a good idea in the Florida climate, Jurewicz agreed that common sense and good design will protect the building’s envelope and the surrounding environment. Minimize western exposure, she said. Be sure to use shading devices. We have a responsibility to take care of our buildings and our environment. Remember codes are just the minimum standard. We can always do better.