Building Science Corp. Rep Addresses Fundamentals and Fallacies for Building Envelopes
June 26, 2012

by Erica Terrini, eterrini@glass.com

Joe Lstiburek, engineer for the Building Science Corp., offered a session called "Don't Do Stupid Things" during today's WDMA opening session.

The 14th annual Window & Door Manufacturers Association (WDMA) Technical Conference is underway today in Bloomington, Minn., and the opening general session, “Don’t Do Stupid Things,” featured Joe Lstiburek, engineer for the Building Science Corp. and an ASHRAE fellow, who focused on issues with basic fundamental requirements for building envelopes.

The long-standing but nonetheless essential roles of windows, as Lstiburek described them, are to control heat flow, airflow, water and vapor flow, rain, ground water, light and solar radiation, noise and vibrations, contaminants, environmental hazards and odors, insects, rodents and vermin, fire; provide strength and rigidity; and, lastly, to be durable, aesthetically pleasing and economical.

“[The window and building envelope industries] do fine with the bottom of this list but really poor at the top of this list,” Lstiburek said. “[The window industry is] in the building enclosure business and has to understand how its products interact.”

According to Lstiburek, in building envelopes, it is the water control layer that trumps the air control layer and rounding out the bottom of top three concerns is the vapor control and lastly the thermal control layer.

“In the grand scheme of things window products are big thermal holes,” he says. “But windows can do other things that walls can’t and it’s the connection between these two industries that is most important.”

Lstiburek says the key to strengthening building and window designs and products overall is to connect all control layers within all areas of a building (walls, windows and roofs). He says there is a disconnect between product manufacturers and building engineers that leads to a mismatch of buildings and the inclusive products used in their design.

“Wouldn’t it be nice if [manufacturers] labeled the windows before shipping them out?” Lstiburek asked. “One problem is [manufacturers and engineers] don’t tell people what should be used with what and no one takes responsibility for where their products go.”

Lstiburek said there needs to be a mutual understanding across the board that control layers need to have matching corresponding products. If manufacturers would provide details on how the products worked, structural engineers might be able to utilize energy-saving designs.

“[Window manufacturers have] gone to great lengths to create phenomenal glazing systems but they are pointless unless thermal breaks in the curtainwall correspond,” he said.

Additionally, Lstiburek said while window manufacturers may make efficient products, insufficiencies in the wall interface cause those products to fail or stress the products beyond their capabilities.

“To be real blunt about it, manufacturers need to be more precise and accurate in their installation instructions and users need to read them,” Lstiburek said.