how to extreme

Patching Rotted Window Sills

Construction How-To, Windows & Doors September 24, 2015 Sonia


 

 

 

 

 

 

 

By Rob Robillard

Wood windowsills take a beating from Mother Nature. Although sloped by design, a windowsill is still basically a horizontal shelf where water and snow can accumulate. Once water finds its way behind trim or beneath paint and caulk, the rot process begins. Ongoing exposure to this moisture will cause the windowsill to decay and worsen over time. When caught early, often a small epoxy repair is all that is needed. But when discovered late or left unchecked, the rot will penetrate deeper into the windowsill and even the wall framing, requiring much more extensive and more expensive repair later.

Repair or Replace

The age-old debate of window replacement or window repair is a tough one to answer, but I’ll explain how I try to guide my client’s decision process.

I look at the repair versus the replacement question as a business approach. What makes the most sense; based on time, budget longevity, and of course hidden costs.

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Occasionally wood rot only occurs at the nose of the window sill.

When dealing with old historic windows, often times repairing is the only option. Many times these windows are protected by a city or town’s historic district commission specifying that the window details remain unchanged. Often times, replacement requires having a custom and costly window fabricated to match the style, look and dimensions of the existing old windows.

Other circumstances where repairing may be an option is on higher-end homes with large expensive units, bay windows or multiple mulled windows. Many times these windows will have high-end trim, wainscoting or faux wall finishes that would add a multitude of extra costs if the window is replaced.

I often opt for window replacement when the cost of the window, any interior work relating to the replacement and my replacement labor are equal to or less than the time I’d spend performing a quality repair. I often see this as a realistic option on more modern homes when dealing with stand-alone window units and simple interior finishes and trim.

 

Replaceable Sill Nosing

Sometimes a windowsill has rot on the outer nosing only. Many newer windows actually have removable nosing that can easily be duplicated and replaced with Western Red Cedar, Mahogany or PVC. Others are designed as one piece and need to be cut away and patched.

Notch out the rotted areas of the nosing and replace with a matching wood patch.

Notch out the rotted areas of the nosing and replace with a matching wood patch.

Rot that occurs deep inside of the sill is more difficult to repair.

Rot that occurs deep inside of the sill is more difficult to repair.

Before working on the sill, seal off the house interior from dust.

Before working on the sill, seal off the house interior from dust.