What is the best insulation for sash windows?

Insulating sash windows is essential for maintaining a consistent temperature inside your home, preventing drafts, and minimising heat loss in the colder months. The right insulation solution can also help to reduce noise pollution and increase the overall value of your property. But with so many options available, how do you choose the best insulation for sash windows? We’ll delve into the pros and cons of various materials, including the popular choices of double-glazing, draught-proofing, and secondary glazing.

insulation for sash windows

Importance of insulation for sash windows

Insulating your sash windows is crucial for several reasons. Firstly, it helps to maintain a comfortable temperature inside your home by preventing heat loss during the colder months and heat gain during the warmer months. This means you can enjoy a consistent temperature throughout the year, regardless of the weather outside.

Secondly, insulation helps to eliminate drafts, which can be a common issue with older sash windows. Drafts not only make your home less comfortable but also waste energy as you need to use more heating or cooling to compensate for the air leakage. By properly insulating your sash windows, you can significantly reduce drafts and improve the overall energy efficiency of your home.

Lastly, insulation can also help to reduce noise pollution. If you live in a busy area or near a main road, the soundproofing properties of insulation can make a noticeable difference in creating a quieter and more peaceful living environment.

Now that we understand the importance of insulation for sash windows, let’s explore the different types of insulation available.

Types of insulation for sash windows

When it comes to insulating sash windows, there are several options to choose from. The most common types of insulation for sash windows include fibreglass insulation, cellulose insulation, and spray foam insulation. Each material has its own pros and cons, so it’s important to consider your specific needs and budget before making a decision.

Fibreglass insulation for sash windows

Fibreglass insulation is one of the most popular choices for insulating sash windows. It consists of fine glass fibres that are woven together to create a fluffy material. Fibreglass insulation is relatively affordable and easy to install, making it a convenient option for homeowners.

One of the key advantages of fibreglass insulation is its thermal performance. It has excellent insulating properties and can effectively reduce heat transfer, keeping your home warm in the winter and cool in the summer. Additionally, fibreglass insulation is non-combustible, meaning it does not contribute to the spread of fire.

However, fibreglass insulation does have some drawbacks. It can be itchy and irritating to the skin, so it’s important to wear protective clothing and gloves when handling it. Fibreglass insulation can also settle over time, reducing its effectiveness. Regular maintenance and proper installation are necessary to ensure optimal performance.

Cellulose insulation for sash windows

Cellulose insulation is another popular choice for insulating sash windows. It is made from recycled paper products, such as newspapers and cardboard, which are treated with fire retardants to enhance their safety.

One of the main advantages of cellulose insulation is its eco-friendliness. By using recycled materials, cellulose insulation helps to reduce waste and minimize environmental impact. It also has excellent thermal properties, providing effective insulation for sash windows.

Cellulose insulation is typically blown or sprayed into the window frame, filling any gaps and creating a barrier against heat transfer and drafts. Its dense composition also helps to reduce noise penetration, making it a great option for noise reduction.

However, cellulose insulation may not be suitable for every situation. It requires professional installation, as it needs to be properly applied and compacted to ensure optimal performance. Additionally, cellulose insulation can settle over time and may need to be topped up or replaced to maintain its effectiveness.

Spray foam insulation for sash windows

Spray foam insulation is a versatile option for insulating sash windows. It is made by mixing two chemicals that react and expand, forming a foam-like substance. Spray foam insulation offers excellent thermal performance and can effectively seal gaps and cracks in the window frame.

One of the main advantages of spray foam insulation is its ability to conform to irregular shapes and sizes. It expands to fill even the smallest gaps, creating an airtight seal that prevents drafts and heat loss. This can result in significant energy savings and improved comfort in your home.

Spray foam insulation also has excellent soundproofing properties, reducing external noise and creating a quieter living environment. It is durable and long-lasting, requiring minimal maintenance once installed.

However, spray foam insulation can be more expensive compared to other options. It also requires professional installation, as the chemicals need to be accurately mixed and applied. Improper installation can lead to issues such as an incomplete seal or excessive expansion, so it’s important to hire a trained professional for the job.

Benefits and drawbacks of each insulation type

Now that we’ve explored the different types of insulation for sash windows, let’s summarize the benefits and drawbacks of each option.

Fibreglass insulation


  • Excellent thermal performance
  • Non-combustible


  • Can be itchy and irritating
  • Settles over time, reducing effectiveness

Cellulose insulation


  • Eco-friendly
  • Excellent thermal and soundproofing properties


  • Requires professional installation
  • May settle over time and require maintenance

Spray foam insulation


  • Excellent thermal performance
  • Conforms to irregular shapes and sizes
  • Provides airtight seal against drafts


  • More expensive
  • Requires professional installation

Factors to consider when choosing insulation for sash windows

When selecting the best insulation for your sash windows, it’s important to consider several factors. These include:

  1. Budget: Determine how much you’re willing to spend on insulation, taking into account the long-term energy savings it can provide.
  2. Climate: Consider the climate you live in and the specific insulation needs for your region. For example, if you experience extreme temperatures, you may require insulation with higher thermal resistance.
  3. Noise reduction: If noise pollution is a concern, look for insulation options that offer excellent soundproofing properties.
  4. Energy efficiency: Choose insulation materials with high R-values, as this indicates greater resistance to heat transfer.
  5. Maintenance: Consider the maintenance requirements of each insulation type, as some may require regular upkeep to maintain their effectiveness.

By evaluating these factors, you can make an informed decision and select the insulation solution that best suits your needs and budget for sash windows.

Hiring a professional for insulation installation

While some insulation options can be installed by homeowners, it’s often beneficial to hire a professional for the job. Professional insulation installers have the knowledge and expertise to ensure proper installation, maximising the effectiveness of the insulation and minimising the risk of issues such as air leakage or incomplete seals.

When hiring a professional for insulation installation, consider the following:

  • Experience: Look for a reputable company or individual with experience in insulating sash windows specifically.
  • Credentials: Ensure the installer has the necessary certifications and licenses to perform the job.
  • References: Ask for references or testimonials from previous clients to gauge the quality of their work.
  • Cost: Obtain quotes from multiple installers to compare prices and ensure you’re getting a fair deal.

By hiring a professional, you can have peace of mind knowing that your sash windows will be properly insulated, maximising energy efficiency and comfort in your home.

Key Takeaway

In conclusion, choosing the best insulation for your sash windows is crucial for improving energy efficiency, reducing drafts, and enhancing the overall comfort of your home. Fibreglass insulation, cellulose insulation, and spray foam insulation are all viable options, each with its own benefits and drawbacks.

Consider factors such as budget, climate, noise reduction, energy efficiency, and maintenance when selecting the best insulation solution for your sash windows. Additionally, hiring a professional for insulation installation can ensure optimal results and minimize the risk of installation issues.

Ultimately, the best insulation for sash windows will depend on your specific needs and budget. By making an informed decision, you can create a more energy-efficient and comfortable living space, while also reducing your environmental footprint.

So, whether you choose fibreglass insulation, cellulose insulation, or spray foam insulation, take the first step towards enhancing the insulation of your sash windows and enjoying the many benefits it brings.