Finish Architectural Knowledge Base
What are the Window Shim Material Types?

Window shim material types vary depending on their application. They are essential tools in the construction and renovation sectors, designed to create a level and stable frame for windows and doors. Typically crafted from materials such as metal, plastic, or wood, the strengths and applications of these shims can vary significantly based on their function.
For instance, fire-rated metal window shims are commonly employed in new construction projects, offering exceptional durability and safety features that comply with building codes. On the other hand, wooden or plastic shims are often preferred for temporary adjustments, providing flexibility in non-load bearing settings. Understanding the right type of shim for a specific application is crucial for achieving optimal structural integrity.

What are the Benefits of Metal Window Shims?
Metal window shims are typically used for the more load bearing projects, high-rise buildings are a prime example which are required to specifically use fire-graded window shims.
High Fire Safety Rating
A high fire rating is now essential for window shims, similar to other building materials used in a high-rise building. Since the Grenfell Tower tragedy in 2017, building regulations have been updated to reflect a change of flammable materials, so new buildings now require non-flammable A1 shims as standard. Such building materials that require a fire rating undergo EN 13501-1 fire testing and for buildings that are taller than 11 metres, materials are required to achieve an A1 fire rating. This is something that cannot be achieved by plastic or wood, hence why they are no longer suitable.
Durable and Long-lasting Properties
Compared to plastic and wood, metal window shims exhibit significantly higher durability, making them a preferred choice for various construction projects. Typically crafted from materials like aluminium or steel, these shims are engineered to withstand substantial weight and pressure, making them ideal for high-load applications. Unlike their plastic counterparts, which can warp or degrade over time, or wooden shims that may absorb moisture and swell, metal shims retain their structural integrity even in challenging environments. Their resilience ensures a long-lasting solution for levelling and stabilising windows and doors, contributing to the overall strength and longevity of the installation.
Corrosion Resistance
Metal window shims exhibit exceptional corrosion resistance, making them ideal for various applications in construction and maintenance. This durability is significantly enhanced through specialised treatments, ensuring they withstand harsh environmental conditions. As a result, they provide reliable support and stability, prolonging the lifespan of windows and improving overall structural integrity.
What are Plastic Window Shims used for?
Plastic shims are typically used in a similar fashion to metal shims. However, due to their material composition, they cannot be used in buildings that exceed 11 meters in height because of their flammable properties.
This limitation is crucial for ensuring safety and compliance with fire regulations in construction projects.
Disadvantages of Plastic Window Shims
Although they are lightweight, their low fire resistance is not suitable for applications where fire safety is crucial. Under large amounts of pressure, plastic shims can also compress or deform, affecting their long-term performance.
Plastic shims could be used for temporary fixes or light load applications (within building regulations), but when concerning taller buildings, metal shims are the norm.
What are Wooden Window Shims used for?
Traditional wooden shims are typically used for smaller, less strenuous DIY projects, which do not require too much long-term support. They are ideal for levelling furniture, door frames, or cabinets where precision is needed. However, for heavy-duty applications, you should consider using metal or composite shims for enhanced durability and stability.
Disadvantages of Wooden Window Shims
Like plastic shims, wooden shims are also not an ideal choice compared to metal shims, especially for the long term. The wood can absorb moisture from the environment, which ultimately leads to rot and decay, diminishing their structural integrity and effectiveness. This means that wooden shims will need to be replaced more frequently, resulting in additional maintenance costs and labour.
Furthermore, wooden shims are not suitable for all applications; they may not provide the necessary strength or stability required in heavy-duty settings, such as in construction or machinery. In contrast, metal shims offer superior durability, resistance to environmental factors, and longevity, making them a more reliable choice for various industrial and commercial applications. While wooden shims can be useful in certain scenarios, their limitations in terms of longevity and versatility make metal shims a preferred option for most long-term projects, ensuring reliability and minimising the need for frequent replacements.
Where can I Buy Window Shims?
At Finish Architectural, we know the best product for window installation are our high-quality horseshoe shims. Either made from aluminium or steel, our fire rated, and durable window shims are the perfect solution for your installation requirements. We also offer a range of finishing options for increased durability and corrosion resistance.
Our professional team can help you decide the suitable solution for you, reach out here.
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