Wednesday, July 1, 2009

Why Windows And Doors Rot

Nothing can be more frustrating to a homeowner than discovering window and door rot on their home. After spending thousands of dollars on painting every 3-5 years, the homeowner begins a futile process of replacing rotted window and door frame components. In some cases the window and door is rotted beyond repair and replacement is the only solution. Here are some of the primary causes-

Improperly Flashed or No Flashing- In all applications a wood framed window or door must have a drip cap or metal Z flashing installed above the exterior casing. This flashing should go behind the exterior finish surface (siding, stucco) and extend out from the exterior wall and then down across the face of the exterior trim (1x4, brickmold). Without flashing, water can penetrate the joint above the window or door allowing moisture to contact what is often unfinished wood.

Unit not Level, Plumb, and Square- All windows and doors are designed to be installed level, plumb and square. They are also designed to shed water. That is why window and door manufacturers stress this repeatedly in their instructions. Think of a door or window as a square within a square, if sashes and door panels do not fit tightly and evenly to their frames they can allow water to penetrate the opening causing damage to unfinished wood.

Poorly Caulked- Often, exterior caulking used during the construction of the home is often the wrong type or improperly applied. Door frames and thresholds are the most susceptible and require proper attention to all seams. The American Architectural Manufacturers Association requires that all exterior sealants used in the installation of windows and doors meet the standard ASTM-920C. This rules out all latex sealants as well as some silicone based sealants. Always check the package to make sure that the sealant that you are using meets these criteria.

Window or Door Not Finished to Manufacturers Specifications- Most window and door manufacturers require a minimum of 2 coats of high quality exterior paint in addition to a base primer which may or may not be provided by the manufacturer. Unfortunately this is rarely done in the new construction process resulting in the topcoat of paint not bonding to the wood surface allowing water to penetrate the raw wood.

Frame and Component Improperly Sealed During Manufacture- Builder grade or shop built wood window and doors are rarely sealed where frame and components intersect. This includes casing miters, main frame members, mullion/casing-sill and threshold-frame joints. Once water penetrates these joints it allows the wood to “wick” water into the end grain of the wood beginning the rot process.

Inferior Frame Material- Most of today’s wood framed window and door products are assembled using fast growth wood. Fast growth wood is a much softer wood compared to the older growth wood used as recently as 25 years ago. This makes the finishing process a critical step in protecting the frame from rot. Improperly finished fast growth pine can fail in as little as 5 years.

Lack of Maintenance- Wood framed windows and doors built within the last 25 years should be inspected on a yearly basis. Check brickmold and casing miters, mullions, jambs and sills for soft areas using a sharp nail or ice pick. Pay attention to where jamb members meet the sill and threshold. Screens should be free of debris and be able to “weep” or drain water to the exterior.

Unfortunately shop built or builder’s grade wood framed window and doors have a short lifespan even with great care. Preventative maintenance can help extend the life of these products but they will eventually need to be replaced.

You can learn more about these and other door and window related issues by visiting