Bob Wewer Discusses Siding Leaks and Issues

Bob Wewer Discusses Siding Leaks and Issues

Exterior cladding has changed much from the days of old. The old clapboard that shed water away from the building has been replaced with products that have been developed to mimic the look of the old clapboards. The mimicking of the look is all that is similar, however. The products of today, primarily vinyl siding has taken hold and the lowered price of these products has attracted many to have them installed onto their buildings. Speaking strictly from a mechanical perspective, the mechanics of these products are troublesome.

The relative thermal movement of the PVC based materials is extreme. This fact necessitates the use of large channels for coverage of the thermal movement. These channels installed around doors and windows are referred to as 'J' Channels. The 'J' Channel borders are similar to the prior cousin of vinyl, that of aluminum siding but they are larger.

Water on the vertical does not collect like that of the plane of a roof but it does collect and roll down unprotected walls. The 'J' Channels form a collection “gutter” at the tops of windows and doors. The water that is collected is deposited to the sides where water runs down the inside of the channels and makes its way onto the wall beneath the siding. Here water is inhibited by the contact of the horizontal coursing and lateral flow is realized. Water continues downward to the next obstruction, namely a window or even a shed roof and then it can enter the wall cavity, if it has not yet done so.  The image on the right depicts the proper head flashing.  The left depicts "J" Channels collecting water.

The reliance of underlayments in the industry has been long known for the prevention of leaks. The “Weather Barrier Statement” was issued by the Vinyl Siding Industry to put the responsibility upon the installer to provide a significant underlayment to prevent leaks. Since a true watershed has not been provided and the underlying walls are vulnerable, this statement addresses the Vinyl Siding as a “Supplemental Rain Screen.” Whether intentional or not the confusion with Screen Wall applications has led some to hail the siding as having good qualities of allowance of “drying” behind the siding.

Wood Siding Leak from lack of Head Flashing.  When Windows were replaced under warranty from rotting issues, manufacturer sent out a window that did not install head flashing:

Just a bad Wood siding job where round window was left to channel water under siding:

 Aluminum Siding with 'J' Channels buried:

Vinyl Siding does not provide a Screen Wall as this is a totally different architectural term referring to brick walls and the like, where a significant air space is allowed totally independent of the cladding. Proper head flashings are impossible because of the channels that collect water. These channels are installed over the head flashings and no return flange over the siding is provided to direct the water back out and over what should be the primary cladding (referred to as Supplemental Rain Screen).  Wood siding installations also if the installer does not realize that a proper head flashing is needed and how to install one (As seen above).

Water volume and velocity cause lateral spreading of water. This has been known for centuries. The propensity for velocity is great with the vertical nature of the wall. The volume is supplied by the water rolling down the wall being collected at the channels. No underlayment can stop this water flow. New products have been invented that claim to “flash” windows by taping underlayment to the wall at the penetrations. The term “flashing” is inappropriate as this term always refers to the primary element that is incorporated into the primary element, which should be the siding. Once the water is introduced beneath the siding it can enter the wall cavity. Leaks often go unnoticed for years unless they fall where there is a shed roof and living areas are located below the wall plane. Then the leak shows on the ceiling and remedy is requested. Repair usually involves convoluted measures to direct water out and onto a roof or down a wall underlayment (somewhere water should no be in the first place). No caulking can fix these leaks and many times it makes them worse as lateral flow is accentuated (like your thumb put over a water hose). Trapped water often finds its way to the wall cavity even traversing uphill (capillary action) to arrive inside the building envelope.  Mold and mildew and wood rot can develop in these situations.

This problem has caused a new wave of underlayments and measures to secure the water-tightness of a structure. We call this “The Underlayment Craze,” by Bob Wewer