How do you insulate Victorian sash windows?

Keeping a home cosy and energy-efficient is a priority for any homeowner. Victorian sash windows are beautiful, but their age and design can make them less efficient at maintaining a comfortable indoor temperature. If you’re looking for ways to improve insulation while preserving the windows’ historical charm, this comprehensive guide is for you.

Victorian Sash Windows

Understanding the Victorian Sash Window Structure

Victorian sash windows are known for their elegance and aesthetic appeal, often found in older homes and heritage buildings. Their structure includes two movable panels or “sashes,” which glide vertically within the frame. While these windows add a touch of timeless beauty, their design characteristics can make them prone to draughts and heat loss.

Anatomy of a Sash Window

Understanding the key components of sash windows can be helpful. The framework comprises:

  1. Upper Sash: The top, movable part.
  2. Lower Sash: The bottom, movable part.
  3. Sill: The bottom horizontal part.
  4. Jambs: The vertical sides of the frame.

Being aware of these components can be beneficial when evaluating insulation options.

Why Insulate Your Victorian Sash Windows?

Insulation of Victorian sash windows serves a dual purpose. Firstly, it makes the home more comfortable by reducing draughts and keeping the warmth where it belongs—inside. Secondly, it can lead to substantial energy savings. Properly insulated windows can dramatically cut down your heating and cooling bills, making the investment a financially sound decision.


One of the most straightforward and cost-effective ways to insulate Victorian sash windows is draught-proofing. This involves sealing all the tiny gaps that let air seep in or out.

Materials You’ll Need

Step-by-Step Guide

  1. Clean the frames and sashes to remove dirt and old paint.
  2. Apply self-adhesive weatherstrips along the sashes’ sides, ensuring a snug fit.
  3. Insert draught excluders at the top and bottom of the sashes.
  4. For any remaining gaps, silicone sealant can offer an additional layer of protection.

While draught-proofing seems easy, the effectiveness highly depends on the condition of your windows. For older or damaged windows, professional consultation is advised to assess the best course of action.

Secondary Glazing

Adding a second layer of glass or clear plastic inside the existing frame is known as secondary glazing. This method is particularly useful for improving the thermal efficiency of Victorian sash windows.

Why Consider Secondary Glazing?

  • Excellent heat retention
  • Additional soundproofing
  • Minimal alteration to the original window design

Implementation Steps

  1. Measure the frame carefully.
  2. Choose your secondary glazing material. Glass is more durable, but plastic is lighter.
  3. Attach the secondary glaze to the inner part of the existing frame using a suitable fixing method.

While the concept seems simple, the installation process can be complicated. The work often involves precise measurements and careful handling of materials, making it advisable to seek professional help.

Thermal Curtains and Blinds

If physical modifications to your Victorian sash windows are not an option, consider thermal curtains and blinds as an alternative. These special window coverings provide an extra layer of insulation without requiring changes to the window itself.

How Do They Work?

  • Thermal curtains have a lining that adds a layer of insulation.
  • Special thermal blinds work by trapping air between the window and the blind, reducing heat loss.

Installation and Care

Installing thermal curtains and blinds is relatively straightforward. However, remember to:

  • Measure your windows accurately before purchasing.
  • Close the curtains or blinds when it’s dark or very sunny for maximum efficiency.

Final Word: DIY or Professional Help?

Several methods to insulate your Victorian sash windows might appear simple, but the reality is that these windows require special care due to their age and design. A professional can provide an in-depth assessment, ensuring that you choose the most effective and suitable insulation method for your particular needs.


Victorian sash windows are an architectural treasure that adds unique beauty to any home. However, their insulating properties often leave much to be desired. With a range of solutions available, from draught-proofing and secondary glazing to thermal curtains, you can improve your home’s thermal efficiency without compromising the historical value of these stunning windows. And while it may be tempting to go the DIY route, due to the complexity and delicate nature of these windows, professional guidance is often the wisest choice.