Rotten Window Frames: Causes, How to Fix & Required Tools

Call Us Today 07565028004

Welcome to Sash Window Refurbish

Experts in Sash Windows Repair & Restoration, Timber Windows & Timber Doors in east midlands

Why Trust Sash Window Refurbish?

Sash Windows Refurbish specializes in providing repair and restoration services for wooden windows and doors in the UK, as well as various types of carpentry. During the process of fulfilling orders, we utilize a range of tools and paints, including saws, sprays, primers, resins, and adhesives. With more than 20 years of experience in carpentry, we have tested and used various brands and types of work tools, making us well-equipped to offer helpful advice on selecting the right tools and paints for your needs. Read more ...

Identifying Rotten Window Frames: Signs and Symptoms

To identify potential wood rot in your window frame, first, inspect the paintwork and exposed surfaces for discolouration or flaking, which are vulnerable points for rot to enter. Press these areas with a tool or finger – healthy wood won’t give way, but rotting wood will depress easily. Pay close attention to intersections of decorative elements, as they are prone to rot and difficult to reach during maintenance.

Wet rot on the window frame

Additionally, watch out for water stains around frames or wet patches below them, indicating advanced decay. Most wooden windows in the UK are made of dense hardwood, so softness or brittleness in healthy wood is unusual. Check common problem areas like bottom corners, sill, and lower stripes. Use a chisel to test suspect areas; if the wood isn’t solid, it’s a sign of rot.

Understanding the Causes of Wood Rot

Wood rot is caused by exposure to water, particularly in damp conditions. Wooden structures, like windows, can absorb water when exposed to severe weather or cracked paint. The moisture content in wood fluctuates based on humidity and seasons. In England, exterior wood maintains 9% to 14% moisture content if protected.

If moisture rises above 20% due to a lack of protection, dry rot can thrive. Keeping wood within 9% to 14% moisture content is crucial for preventing rot, warping, and cracking. The moisture content of 40-60% creates conditions for wet rot to become a serious issue.

The Role of Moisture Content in Timber Window Frame Deterioration

Moisture content in timber window frames plays a significant role in their deterioration. High moisture levels create conditions conducive to rot. Using a wood moisture meter is an effective way to measure and monitor moisture content, allowing homeowners to take preventive measures and maintain the optimal conditions for their wooden windows.

Using a Wood Moisture Meter for Diagnosis

A wood moisture meter is an invaluable tool for diagnosing the extent of moisture infiltration in wooden window frames. By accurately measuring moisture levels, homeowners can assess the severity of the issue and determine the appropriate course of action, whether it’s repair or replacement.

Effective Strategies for Repairing Rotten Window Frames

Several strategies are available for repairing rotten window frames, ranging from wood treatments to partial or complete replacements. Wood treatments can help preserve the remaining sound wood, while techniques like reversing wet rot or using epoxy wood fillers can restore the damaged sections, providing a cost-effective solution.

Exploring Solutions for Rot Repair on Wooden Windows

Repairing rotten window frames involves exploring various solutions. Reversing wet rot by eliminating the moisture source and applying fungicidal treatments can halt its progression. Epoxy wood fillers are excellent for repairing localized rot, providing a sturdy and durable fix. Partial replacements involve replacing only the damaged parts, whereas complete frame replacements offer a comprehensive solution for extensive decay.

Preserving Wood with Suitable Treatments

Applying suitable wood treatments is essential to preserve window frames and prevent future rot. Wood preservatives and sealants create a protective barrier, making it difficult for moisture and fungi to penetrate the wood. Regular maintenance, including repainting and resealing, can significantly extend the lifespan of wooden window frames.

Addressing Wet Rot: Reversal Techniques

Wet rot, caused by excessive moisture, can be reversed by eliminating the source of moisture and improving ventilation. Proper drainage systems, sealing gaps and cracks, and ensuring adequate ventilation can help prevent wet rot from recurring, safeguarding your windows against further deterioration.

Restoring Rotten Frames Using Epoxy Wood Fillers

Epoxy wood fillers are a popular choice for restoring rotten window frames. These fillers are specially designed to bond securely with wood, creating a strong, long-lasting repair. By removing the decayed wood and applying epoxy filler, homeowners can restore the structural integrity of their window frames and enhance their durability.

Partial Window Frame Replacement: A Repair Approach

When rot is localized, partial window frame replacement is a viable repair approach. This method involves removing only the damaged sections and replacing them with new, treated wood. It preserves the overall appearance of the window while addressing the specific areas affected by rot, making it a cost-effective solution for minor damage.

Complete Frame Replacement: A Comprehensive Solution

In cases of extensive decay, complete frame replacement becomes necessary. This comprehensive solution involves removing the entire window frame and replacing it with a new, rot-resistant frame. While it is a more significant investment, complete frame replacement ensures the long-term stability and functionality of your windows, offering peace of mind for homeowners.

Cost of Repairing Rotted Window Sashes and Frames

If you need to replace a single decayed window sill, sash window companies typically charge approximately £250 for this service. For more comprehensive restoration and repair tasks, which involve activities like splicing and draught-proofing, the cost can go up to around £700 per sash window, excluding the cost of painting.

Regardless of the specific job, it is crucial to invest time and effort in ensuring your windows receive proper care. This proactive approach not only helps you save money in the long term but also guarantees the longevity of your window frames for years to come.

At our wooden window restoration company, we employ various techniques for sash window restoration. You can find detailed information about our sash window refurbishment pricing on our website.

Window Frame Splicing: Repairing Sections

Window frame splicing is a technique used to repair specific sections of damaged frames. By carefully removing the affected parts and replacing them with new timber, this method provides a targeted solution for localized rot. Properly executed splicing repairs can seamlessly integrate new sections, preserving the aesthetic appeal of the window.

Selecting Appropriate Timber for Spliced Repairs

When fixing rotten wooden window frames, it’s best to use the same timber or find a similar high-quality wood with matching moisture content. Avoid weak wood with knot shakes or sapwood. Remove the rotten parts using hand or power tools, then repair them using splice techniques. After glueing the repairs, shape them to match the window frame, sand, fill gaps with wood filler, and finish with painting and priming. Consider applying dry rot treatment for stability during repairs.

Considering Entire Window Replacement

In cases where extensive rot has compromised the entire window frame, considering complete window replacement is a practical choice. New windows made from modern, weather-resistant materials provide superior insulation and energy efficiency. While it involves a higher upfront cost, complete replacement eliminates the risk of future rot and offers long-term benefits in terms of durability and performance.

We strongly advise against DIYers attempting to replace a wooden frame, as it’s a complex task. Window fitters should be registered with organizations like FENCA or Certass for proper expertise and safety.


Understanding Dry Rot in Timber

Dry rot is a severe form of wood decay caused by specific fungi, leading to the deterioration of timber structures. It thrives in damp, poorly ventilated environments and can cause extensive damage to wooden window frames if left untreated. Identifying dry rot early and addressing the underlying moisture issue is essential to prevent further damage.

Identifying the Causes of Dry Rot in Timber

Dry rot in timber is primarily caused by a combination of moisture and lack of ventilation. Leaking roofs, plumbing issues, or poor drainage can create the damp conditions necessary for dry rot to flourish. Properly maintaining the structural integrity of buildings and ensuring adequate ventilation can help prevent dry rot and preserve wooden window frames.

Can Rotted Window Frames Be Repaired?

Yes, rotted window frames can be repaired using various techniques such as wood treatments, epoxy wood fillers, partial replacements, or complete frame replacements. The choice of repair method depends on the extent of the damage and the homeowner’s budget. Timely intervention and appropriate repairs can salvage window frames and extend their lifespan.

Methods for Fixing Rotten Wooden Window Frames

Fixing rotten wooden window frames involves a combination of assessment, diagnosis, and suitable repair methods. Homeowners can choose from a range of techniques, including wood treatments, epoxy fillers, spliced repairs, or complete replacements, depending on the severity of the damage. Consulting with professionals can help determine the most effective method for each specific case.

Preventing Window Frame Decay: Effective Strategies

Preventing window frame decay requires proactive measures to control moisture infiltration and improve ventilation. Regular inspections, timely repairs of leaks, adequate ventilation, and application of wood preservatives can significantly reduce the risk of rot. Maintaining a dry and well-ventilated environment around windows is essential for preventing decay and preserving the beauty and functionality of wooden window frames.

About the author

Glen Ramsey, who presently holds the positions of customer support and content manager, is a cherished member of the Sash Window Refurbish team. He is in a unique position to provide advice on all questions pertaining to the renovation of historic windows because he has a wealth of experience in all elements of window renovation, dealing with clients regularly and assisting them in choosing the best window-related course of action. He oversees the creation of information for all of our platforms in his capacity as content manager, including web content and other materials. Glen has witnessed the whole gamut of Sash Window Refurbish's window restoration activities, from our work on significant listed Georgian homes to a wide variety of smaller-scale private residential projects.


My technician Andrew replaced all my sash windows that had rotten sills. Accessing the rotten sills was not an easy task. He explained to me what needed to be done in order to fix the problem. He is a great person and I’m happy that he was the one who did the job. He is reliable, tidy, friendly and very professional. I highly recommend him.



I hired Andrew and Alex a while back to repair my damaged sash windows. They were was very considerate and very patient as he did his job. A few days ago, I had another problem with one of my sash lock keys and I called him again to come and fix the problem. I’m very impressed that Liam responded quickly and he not only fixed the problem but he also gave me a spare key. What a great after sales service!

Alan W.


I’m very impressed with the new windows that Andrew installed and also the reconditioning job that he did on other sash windows. The quality of his work is by far more superior than what we got when we hired another company a few years back. We will certainly hire him again if any window work arises

Kelly (Sleaford)


Our decorator referred us to Andrew because some of the work needed a window expert. Andrew together with our decorator did a fantastic job. The work was done efficiently and to the highest standards. Andrew is understanding, committed and very professional. I recommend him without any hesitation.

Steaven Reader


Alex did a great job in fixing windows in our terraced house. The windows were broken, frames damaged and the wood was also rotten. Alex's job was high quality and he did it pretty fast. I was also very impressed that he was considerate of my son’s asthma condition and maintained cleanliness. Top work.



Andrew just recently replaced three sash windows in my Edwardian house. He also repaired and replaced some sills and draught proofed three windows. In addition to that, he also did some carpentry work. What I like the most about Liam is that he did a clean job. He is very professional and always updated me about the timescales and costs. He also did his job with minimal disruptions. I highly recommend him.

Cris M.