Estimating Repair Costs for Rotted Window Sills and Trim

Estimating home repair costs is challenging

When the extent of the damage is not visible, estimating home repair costs presents a challenge. One of the most common handyman projects is repairing rotted window sills. The  extent of the damage in these repairs is often hidden until the rotted wood is removed. Most wood rot is preventable if home owners understand how critical routine, annual maintenance is to protecting their home.

We are accustomed to protecting ourselves from getting wet, except when it’s fun and intentional, like at the beach or  pool. We use umbrellas when it rains. We put wet stuff in plastic instead of brown paper bags. This instinctive stay-dry wisdom does not extend to our homes. We need to learn how to protect our homes from water infiltration. It can persist for years hidden beneath the surface. Close-up, annual inspections are the umbrella that will help us find these problems early and protect our homes from unnecessary water damage.

This article addresses the various levels of wood rot damage encountered by homeowners and handymen. It starts with “routine preventive  maintenance” and progresses to the most severe damage involving not only replacement of the window itself, but replacement of the framework that holds the window in place.

Cracked or Peeling Paint on Window Sills

Although homeowners are accustomed to painting the exterior of their homes periodically, many do not realize that some parts require more frequent attention. The exterior wood surfaces that are most susceptible to wood rot include wood trim that protrudes beyond the siding, horizontal surfaces like window sills and surfaces near the ground subject to splash back.

Annual inspection of these vulnerable areas allows timely repairs, such as painting and scraping at the first sign of damage or potential exposure to water, indicated by cracked paint.

Moisture that rots wood travels and causes more damage when not repaired quickly

Punky (Soft) Wood Pockets

When wood is infiltrated by water, an environment that can sustain fungi and mold is created with the wood becoming a food source. The continued presence of moisture sustains the breakdown of the wood, a mostly invisible process, obscured by paint or hidden deep in the wood.

Required repairs and related costs grow when wood rot in a window sill is left to grow over time:

  • Repair small cracks or chipped paint by scraping all loose paint and applying a high quality exterior paint… in under 30 minutes after assembling tools and materials (always include time to gather materials and clean up).
  • Clean out one or two small (like a golf ball or smaller) pockets of wood rot by removing all damp wood, and fill with an easy to sand and paint product like Bondo (an automobile repair product which forms a nice hard surface)… in under 60 minutes with tools and materials assembled.
  • For more extensive wood rot damage (photo above right), remove and replace one or more pieces of exterior boards. Although, technically, the window should be removed before replacing the sill (3 to 4 hrs), most handymen will do it in place … typically 1.5 to 2 hours, plus shopping.

Rot Can Extend to Vertical Trim Boards

Although most wood rot starts at the window sill, and the damage will spread requiring more extensive repairs. Fortunately, the damage to the vertical trim board in the photo above has not expanded to either side and does not appear to involve the window sill. Repair of the damage in the photo is likely to include replacing the vertical board and cleaning out any punky wood on the sill below (30 to 60 minutes).

When replacing a window sill, this type of repair is often needed. Sill and trim repairs can be completed together in 2 to 3 hours plus shopping time (no standards for window trim thickness). We recommend a composite like Azek with no wood content, to avoid the problem reoccurring. The higher material cost is outweighed by not having to perform annual maintenance.

Wood rot here requires multiple= Rotted Jambs Surrounding a Window

More extensive wood rot is shown in the photo at the left. The damage extended into the jambs which hold the window in place, and required installation of a new window.  Although, technically, a window can be rebuilt, a replacement window costs less than the labor to rebuild. Rebuilding a window makes sense only when the owner of an older home wants to preserve the architecture.

Although the trim pieces you see when you look at a window from the outside are decorative, they have a more important purpose. By covering gaps between the window and siding, they provide a continuous barrier protecting and keeping water out. If moisture extends past any window trim boards (sill and/or vertical trim), wood rot will begin to compromise the wood structure holding the window.

Damaged or Missing Rough Window Framing

The pictures below illustrate the severity of damage that can occur if water damage is ignored for many years. Although the black spots on the Masonite siding were indicative of a problem, the homeowner ignored these signals.  As illustrated by the photos, the entire rough opening, which was to hold the replacement window in place, had to be rebuilt. These repairs are so specific to a situation that  it’s impossible to give typical estimate repair times.

Rotted siding, window trim, window & missing structural framing, a handyman nightmare


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About Dennis Turmel

Dennis Turmel has maintained buildings for many years, with 20+ years at the Eagle Tribune and of course, his own homes. He enjoys working with homeowners to solve problems, or even more fun, update their homes so they'll enjoy them more. Dennis pefers helping home owners with routine home maintenance, to minimize costly repairs and of course, there's less stress.

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