Maintaining Timber Windows

A well-maintained and maintained timber window repair is a crucial element of the historical fabric of a structure. It illustrates in varying degrees the various materials and techniques, craftsmanship and architectural taste of the time from which it dates.

If repairs are possible to existing windows are required, they should be made in situ. Repairing the most severe areas of decay can be done using proprietary resin-based systems.

Durability

Timber windows were built to last for centuries. They do require some maintenance to keep them looking great. Maintenance tasks include sash cord repairs as well as tightening the pulleys for sash and painting. There is also a rising demand for upgrading timber windows to increase the efficiency of energy. This could mean replacing old glazing units, repairing existing window rebates or putting in new cills that allow the air to seal better.

The corrosion of paintwork is a major problem with traditional windows. This is especially important when it comes to sash windows, as the gaps between sashes may be quite large. In these circumstances water can get into the paint film and cause rotting of the putty as well as underlying wood. The rotting process can be made worse by weather conditions that are not ideal. To stop this from happening, windows need to be regularly painted with an exterior wood paint.

In addition to repainting, areas that have corroded need to be repaired with a resin-based repair product. This will ensure that the maximum possible amount of the original fabric remains. It is also essential to limit the number of holes you drill into the frame to allow cable entry, as they could admit water and lead to decay.

Another significant problem with older windows is structural movement in the wall which can cause deformation of the frame and sash. This can result in sash not fitting correctly, jamming or sticking in the opening, or breaking glass. This can often be fixed by fitting new sash boxes constructed from slow-growing deal (pine) or oak. The cill should be constructed of a durable hardwood, like oak, in order to prevent any differential movement between new and old work.

There are a variety of companies that manufacture Boston pattern wooden sash to fit most existing openings. The sash is available in a variety of sizes and finishes that meet the needs of the modern homeowner. The new sash, coupled with quadruple draft strips and improved thermal insulation can significantly improve the energy-efficiency of a home.

Aesthetics

Many old timber frames have a great aesthetic appeal, as they reflect, in some form, the quality of the wood, technology, and architectural style of the time they were built. They could also have a significant historic value in their own right. This is especially true of early unglazed window openings in timber framed buildings where the great majority were simply a series of openings in the structural frame sub-divided horizontally into mullions, and vertically into iron or wood bars to deter intrusions.

Traditional timber window joinery can be a highly decorative feature of a building and is essential to maintain its appearance. It is vital that any decay that results from the penetration of moisture should be immediately stopped once it is identified. It is best to do this through thorough painting, especially where there is damage or deterioration. It is recommended to use paints that are designed to be used in a set (primer undercoat and finish), and to follow the manufacturer’s recommendations for preparation and number of coats at each stage.

The fungus responsible for wet rot can quickly spread in old timber windows. To stop this from happening, remove any damaged or rotten components as soon as you can. The replacement of wood that is rotting must be done with care with a slow-growing deal (pine) and, if possible, the same species as that which is being removed to prevent any movement differences between the new section and existing timbers.

In the late medieval and 17th century periods glass became more affordable and abundant, and the openings for glazed glass in timber-framed buildings gradually became elegant with wooden tracery moulded mullions, moulded mullions, and deep protruding cills. In recent years, glass was pinned into rebated frames with cambridge double glazing sprigs, not lead cames. This method of glazing is not just less prone to leaking but also allows for larger and clearer sheets of glass to be used in the windows than would otherwise have been possible without the need for leaded lights.

Energy efficiency

Traditional timber windows provide a good energy performance due to their thickness and multi-layer construction, as well as careful attention to detailing. They also have large glass areas and projecting cills that minimise air infiltration. With secondary glazing and draughtproofing the windows can be improved to improve their energy efficiency. It is important to remember that these measures should be considered in relation to the overall integrity and look of the original windows.

Therefore, keeping the existing windows from the past that require repair rather than replacing them makes sense, particularly when their thermal enhancements can be achieved economically through simple repairs and improvements. Historic windows are often of historical value, as they demonstrate a variety in technical development and changes to architectural style. The pressure to replace these windows are usually based on the assumption that the old windows will need replacement in the near future, however most are still capable of serving for 150, 200 or even 250 years if they are properly maintained.

It is important to recognize that decay issues with traditional timber windows are preventable by timely and thorough repairs. In addition it is vital to recognize damp penetration issues and to remedy them quickly to avoid major damage. The early deterioration of paint is a major issue, because it allows moisture to penetrate the wood and cause wet rot. It is not uncommon for this damage to go unnoticed until the paintwork begins to crack or become wavier. However, it could cause structural damage and then further decay.

A paint of good quality will stop moisture from entering the paint. To prevent mould and condensation, it is important to keep the paintwork as clean as you can. Modern synthetic paints can be problematic, as they are often made to be water-resistant and this may result in the formation of mildew inside the window frame.

Most older windows were made from sapwood-rich wood. The timbers will deteriorate quickly when exposed to wet weather conditions, but they can be protected with a thorough treatment of preservative before they are put to use. It is also essential to ensure that the type of wood used is suitable to the climate and site conditions, as these elements can affect the longevity of the joinery. Local window manufacturers offer a wide range of sash made from timber that can be customized to fit historic openings. They can be produced in the standard Boston pattern or in custom sizes to fit historical structures.

Maintenance

Regular inspections, careful redecoration, and prompt repairs can extend the life of timber windows. The most common reason for the decay is the infiltration of moisture through deteriorated putty and paint. This can be avoided by using a high-quality wood preservative and painting the wood thoroughly.

It is important that repairs to the old sash and casement windows are well executed and completed without causing any disturbance. Repairs can be made to several traditional designs of timber windows without taking the frame off. This should be done whenever possible. Paint that is peeling or loose must be removed with care and sanded lightly to increase the 'key' of the surface, allowing for an easier adhesion of the new coating. It is crucial to avoid removing old paint layers, as they may have historical value.

When a section of wood has rotted the best way to deal with it is to take it off and replace it with timber inserts designed to match existing profiles. The timber that is inserted should be treated with wood preservative and the junction between the masonry sub-cill and the timber cill should be sealed.

Replacement of traditional windows using PVC-u may be a tempting option, especially when the installer offers an "all-in-one" installation that handles removal and replacement within one day. It is crucial that installers of replacement windows have a thorough understanding of the history and design of traditional timber frames. This will allow them to make appropriate recommendations for energy-efficiency improvements and other technological advancements that won't harm the character of a building that is historic. The windows that are replaced should be registered under a Competent Persons Scheme, such as FENSA. This will ensure that the replacements are deemed to be approved by the Building Regulations as a suitable alternative. It is quite possible for a skilled and experienced carpenter to install PVC-U windows that are sympathetic to the the original building. This is especially relevant when windows are situated within listed buildings or conservation areas.