The Barrier Approach
This approach works under the preconception that the installation will keep all the water out and is the approach traditionally used by much of the industry. In this approach, the window is sealed on all four sides in an attempt to create a perfect barrier against water infiltration. Experience has shown that most window installations do not have the ability to perform as a perfect barrier for the life of the window installation.

In addition, the ability to actually create the barrier is undermined by damage to or flaws in the frame of the window and door product either from manufacturer or on-site damage or both. Due to this, barrier systems, while a form of water management, are not generally recommended and should only be considered for use in certain assemblies such as mass wall assemblies.

Most standards and practices for window and door installation focus on barrier techniques. This is due primarily to two reasons. First, theory and lab observations allow barrier techniques to work as designed. This is not true in the field. Second, window manufacturers are primarily concerned (understandably) that their productsdo not leak, and little concern for the performance of the wall.

The Drainage Approach
Drained systems work under the concession that some water will leak through the window at some point in time, and provisions are to be made to direct the water back out to the exterior. This approach has been shown to be an effective method of water management, though care must still be taken in the design and application of the system.

While the construction of the wall and the application of the various wraps, barriers, and flashings on the wall are the responsibilities of others, the WINDOW FITTERS trained installer can mount the new window and door into the opening, and make sure that any water that enters is directed away from the interior and is given a path to drain properly to the exterior.

And, the WINDOW FITTERS trained installer can take care to maintain vapor barrier continuity to be sure any migration of moisture is out of the cavity between the window/door and the opening to a place where it can drain, dry or be absorbed to eliminate chance of rot, mold or other damage in the wall structure.

The WINDOW FITTERS drainage method, when its techniques and materials are applied to the window or door opening, assure that the installation will not leak, and that damage to the materials within the opening cavity are mitigated. It is the best method over the long haul, and superior to the barrier method in today’s energy efficient constructions.

Vapor Barrier Control
The function of a vapor barrier is to retard migration of water vapor. Where it is located in an assembly and its permeability is a function of climate, the characteristics of the materials that comprise the assembly and the interior conditions. Vapor barriers are not typically intended to retard migration of air. That is the function of air barriers.

The fundamental principle of water control in the vapor form is to keep it out and to let it out if it gets in. This becomes complicated because the barrier method of window installation used in the past meant to keep water vapor out was found to trap water vapor in. This can be a real problem if the assemblies start out wet because of rain or the use of wet materials, but can be the principle cause of mold, rot and other decay in the cavity between the window or door and the rough opening. Moisture can also lessen the insulation value of fiberglass or other insulation materials placed in the wall.

It becomes even more complicated because of climate. In general, water vapor moves from the warm side of building assemblies to the cold side. This is why insulation battes have building paper type surfaces on one side (used to staple to the studs). Determining the warm side/cold side needs different strategies for different climates, and differences between summer and winter.

For the purposes of window and door installation, WINDOW FITTERS proper installation will maintain continuity in the vapor barrier with regard to the window or door opening making sure any potential moisture migrating into the cavity between the window and door and the rough opening is not trapped, will not condense, and is free to dissipate before it can cause damage. It is an extra step not usually taken by window and installers, but necessary for proper and effective and long lasting installations.