It all came down to lowest foam pressure. The story is common in the construction industry: Work performed by varying trades with varying degrees of skill inevitably leads to a certain amount of failed installations.

In the case of window installation, it can mean moisture intruding into a home around the windows with no means of escape, which then may mean deterioration and expensive callbacks.

Pella Corp. offered a solution: Create a rookie-proof installation system utilizing a flashing tape and foam sealant that both prevent moisture intrusion and help drain out any water that does enter.

"They were looking for something foolproof so the expertise of the person putting in the window didn't matter," explains Mike Dillon, Midwest field seller for the Nash Division of Dow Chemical, the company that developed the Great Stuff foam recommended by Pella in its installation instruction. "That was the reason for developing this system."

Water in

We all know moisture gets into buildings through building openings, especially unsealed window openings. What made Pella's approach unusual was that it acknowledged the issue. Pella designed the installation system on the premise that over time, some water may get in, rather than trying to sell themselves-and the public-that water can be totally prevented from getting in.

"You can't stop it completely," says Cordell Burton, an installation engineer at Pella Corp. "Water will get in through cracked sealants or as a result of errors. So what are you going to do? Protect the openings, drain the water to the outside and let the system dry out."

Three years ago, as part of a new installation methodology, Pella began recommending a flashing method for window openings. The weather barrier is critical as secondary protection, behind the cladding. The barrier is cut in a modified I-pattern as is common with barriers, such as Tyvek. It is wrapped into the window opening at the jambs and sill but is folded up at the head of the opening so that it can wrap over the top window flange. At the same time, the company also introduced a flashing tape, to cover the sill of the window opening.

"If moisture does get in, it is on the sill that damage likely will occur, so that's where we want the protection," adds Burton. "With the tape, we can ‘bend' it around corners, into cracks and crevices. It's thin so it doesn't mess up trims."

Any horizontal surface needs to take drainage into account and move water outside. If one can float the windowsill, all the better. A shim on the top of the sill cripple studs will allow one to get a floating sill, pushing moisture to the outside.

Once the window is in, keep the window off the rough opening. If flat against it, it traps moisture that may not get out. This is critical both to leveling a window and getting moisture out of the opening.

After the window is nailed in place, it is flashed just as one would flash a skylight on a roof. Start at the bottom and work up so everything overlaps.

"Tape the top flange to OSB or plywood at the top of the window and roll the weather-resistive barrier back over the tape. Any moisture on the OSB above the window hits the tape and rolls back out."

Pella left the air cavity in too.

"You want air around the basic perimeter edge so water that is in there can get back out and it can dry out," Burton says.

Polyurethane foam sealant won't hold water.

Foam in

It was coordination with Dow that added foam into the installation process. The foam's purpose is to expand in concealed spaces and fill the space between the wall and window frame, stopping water and air intrusion.

Over the years, foam sealants have had a bad rap in the window industry because over expansion of foam damaged windows.

"In the early days, the foam would expand too much and squeeze the window frame, hampering operation of the window because the foam's pressure caused an uneven frame," Dillon explains.

Years ago, window manufacturers voided warranties if foam was used. Then Pella learned that Dow Chemical had reformulated a foam to generate very little foaming pressure: Great Stuff Pro Window and Door Formulation. Dow understood there was a potential market in the window industry if it offered a product seen superior in its capabilities of air-sealing around a window that would not damage window units. That had been tried before with existing foam but results were lackluster.

"We developed this foam specifically for this application and it performed as we expected it to," Dillon says. "We hoped this formulation would change the minds of the players in the window industry."

Now, many window manufacturers say it's OK to use foam, as long as the installer follows manufacturer recommendations when applying it. Some window manufacturers do not point out a specific product. If contractors follow manufacturers' instructions and do it right, they won't damage a window.

"We went one step further: We made a foam that will work even if over-applied," Dillon adds.

Dillon adds that other window manufacturers are adopting the installation method Pella developed in whole or part.

"Water is going to get into the building envelope," he says. "We need a way to manage it and get it out of the envelope. Just admitting that is such a stride forward compared to the past. Pella spearheaded a change in the industry, not just within their company. They looked at it as providing a useful, reliable process for builders, rather than saying ‘It's your problem.'

"Also, water doesn't always just get in around the windows, it often comes from above the windows," Dillon says. "Gravity will pull water down onto the frame and if not installed with flashing as Pella recommends, water will seem to be leaking through or around the window when it is actually not. With the current method, it's forced back outside."

Air in

The flow of air is also an acknowledged conspirator in moisture intrusion.

"If air is flowing, it can take water with it," Burton says. "If you stop the air, you stop the water. The foam interior seal can stop the airflow. The disadvantages of fiberglass is that it doesn't stop airflow, doesn't have very good R-value and it holds moisture. If moisture gets in, we don't want it held in the opening. Dow's foam is polyurethane and won't hold water."

Other foams, such as latex, hold moisture, resulting in deterioration. Pella specifically wanted a polyurethane foam, which doesn't hold moisture and won't bow the window frame, as even minimum-expanding foam bows windows.

"You want it to expand to stop air but not put pressure on window," Burton says. "It's still a big fear out there as originally, foams bowed windows. We don't have this problem with the Dow product."

The installation system is even effective when used with stucco or synthetic stone, as long as they are drainable systems.

"This installation system is for nearly any drainable cladding systems," says Chris Phillips, strategic programs manager for Pella.

"There is a call for this installation method everywhere in the country, whether in Phoenix or Maine. We want to help stop the callbacks so neither the contractor nor the customer have to worry."