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Guide to Repair Rotted Windowsills and Window Frames

Last Updated on February 26, 2024

Windowsill rot is a critical issue that must be addressed promptly. The rot is caused by fungi, which eat away at the windowsill and the wood frame. Homeowners are advised to repair the rotted windowsills and window frames right away using this handy guide.

Wooden window frames have enormous appeal due to their attractive appearance and their historic feel. However, these aspects of the home are not maintenance-free. Several conditions, from rainfall to sunshine, can take a toll on windowsills and cause them to rot.

What causes windowsill rot?

As mentioned, fungus is responsible for destroying the wood in the windowsills and window frames. Fungi thrive in moist conditions—and when a windowsill exposed to consistent moisture fails to dry thoroughly, it is susceptible to fungal growth and the resulting wood rot.

What are different types of wood rot?

A windowsill is vulnerable to three different types of wood rot. White rot is whitish in color and feels spongy. Wood appears dry when brown rot occurs, and it breaks into pieces due to fungus damaging the structure. Soft rot looks like honeycomb and is not typical on window frames.

What are signs of windowsill rot?

Drafty windows indicate damage to the windowsill. Wood rot can cause shrinkage, leading to the sashes rattling in the frame. Softwood is another sign of rot; the wood feels spongy or soft to the touch. Paint bubbles and swelling that make it difficult to open the window also indicate rotting.

How do homeowners repair a rotted windowsill and frame?

The extent of decay determines the best repair method. Epoxy wood filler is recommended when the wood rot is less than 20 percent. Replace the rotted section of wood when the decay is greater than 20 percent. Full-frame replacement is necessary when the structural components are damaged.

It is always best to have a professional replace a rotted windowsill

Repair Option 1: Apply Wood Epoxy

If you have the skill, you can try using wood epoxy. In some case a strong, durable, and waterproof, wood epoxy fixes small areas of wood rot around windows. First check how deep the decay is by scraping the wood surface with a screwdriver. If the rot is deep-set, forego the restoration; the windowsill is too compromised and requires replacement by professionals instead.

Scrape away the small area of rotted wood with a chisel until all the rot is removed and healthy wood appears. Prep the epoxy per the instructions on the label. Spoon the epoxy into the chiseled spaces, filling in all gaps. Allow the epoxy time to cure. Sand and paint the windowsill once the epoxy is dry.

It is important to remember that wood epoxy may only be effective for fixing small areas of rot, and it must be done properly to have the desired effect. In many cases, it is better for rotted wood to be replaced as even with epoxy it will likely not be a long-term solution.

Repair Option 2: Replace Rotted Sections

The rotted areas of the sill can be replaced but require more skill than applying epoxy. Patching, however is not a lasting fix; replacement should be considered when the wood around the window is rotted.

  • First carefully pry off the rotted boards, minimizing damage to the surrounding wood. Take precise measurements of the rotted wood to ensure the replacement boards are the correct size. Seal any cracks in the sheath around the window with caulk to protect it from further water damage. Obtain new boards from the lumber store and cut them to size.
  • Position the freshly cut lumber into the spaces around the window to ensure it fits. Trim away excess wood; if the wood is too small, fill in the gaps with epoxy wood filler. Tap the board with a hammer to ensure a snug fit against the other pieces of wood.
  • Fasten the board to the home using a drill and wood screws; alternately, a hammer and nails can be used to secure the wood. Apply caulk to any gaps to prevent water intrusion. Paint the boards to match the home and allow it to dry.

Repair Option 3: Full Replacement

Wood rot may require a full replacement rather than restoration when the decay is extensive. A window replacement offers numerous benefits, such as improved energy efficiency, increased home value, and better air quality. Compare the cost of repairing against replacement to arrive at the best decision.

How do homeowners extend the life of the windowsill?

Protect windowsills from rotting by applying a primer to the surface. Add two or more coats of latex paint to serve as a barrier against water. Lastly, seal with a few layers of waterproof sealer to keep out rainwater from the wood.

Additional tips to promote longevity include routinely checking the window frame for cracks and sealing them with caulk or putty. Spray fungicide on the wood surfaces regularly; this step prevents fungi from causing wood rot by eliminating it before it has a chance to react with moisture and cause decay.

Repairing a rotted windowsill and window frame is cost-effective in comparison to a full replacement. Homeowners can attempt the restoration as a DIY project but a professional repair by Arax Windows Work leads to better results so that you can enjoy your windows long-term.

Our restoration crews are skilled in repairing window frames, sills, sashes, and jambs. Rotted window frame repair covers brick molding, middle molding, or inside molding. We source and use only high-quality wood for all our repairs, ensuring the windowsills and frames endure.

Arax Windows Work repair specialists have the skill, equipment, and experience to fix windows of all sizes and strive to maintain their natural look as much as possible. If the wood rot causes damage to the glass, we’re available to replace the window glass, too.

Maintain both the beauty and functionality of your windows with our professional window restoration services. Rather than replacing your home’s damaged windows, affordably repair them to experience equal benefits: enhanced comfort, upgraded energy efficiency, improved security, and enduring aesthetic appeal.

As a leading window frame repair service, Arax Windows Work is trusted by countless residential homeowners. Our commitment to quality service and expert workmanship have earned us prestigious awards from Home Advisor and top ratings from the Better Business Bureau.

Wood windows are susceptible to rotting, especially in geographic areas where weather conditions are severe. If the windows in your Chicago area home have rotted, choose Arax Windows Work for high-quality work, affordable prices, and courteous customer service. Contact Arax today for more information.