When the colder months start to loom, it’s natural for property owners to steer their thoughts towards increasing the energy efficiency of their home. Insulating the windows is a great place to start.

By efficiently insulating windows, you will be:

  • Reducing heat loss from your home, making it more energy efficient. This means you won’t have to rely as heavily on heating systems, which can save you money on energy bills.
  • Helping to maintain a consistent temperature inside your home, making it more comfortable during cold winter months. It also prevents cold draughts from entering your living spaces.
  • Reducing condensation on windows, which would lead to problems like mould growth and damage to window frames and surrounding walls.
  • Lowering your carbon footprint and contributing to environmental conservation efforts.

In this article, we share our professional knowledge on how to insulate sash windows ready for winter.

Window insulation refers to the methods and materials used to reduce heat transfer (heat loss) from a building by providing an effective barrier between the inside (where it is typically warm in winter) and outside of your home (where it is typically much colder during a UK winter). There are various techniques and materials used for window insulation:

Use close fitting window dressings

Close fitting curtains, pelmets, blinds or plantation shutters will provide an additional insulating barrier to your windows when drawn/closed at dusk. They will help to trap the warm air inside your home by preventing it from hitting the colder glass of your sash windows and cooling down. Window dressings can also help to reduce draughts. Keep window dressings open during sunny days where the sun shines through to make the best use of the warmth from the sun.


Trickle vents

All houses need a certain amount of ventilation to prevent the build-up of condensation, as well as removing unpleasant household odours. Badly fitting doors and windows achieve this in an uncontrolled way. Having trickle vents on your windows means you can open some of them in winter and control the amount of ventilation. This will improve air circulation and reduce condensation without losing too much heat. 

Install double glazed sash windows

Did you know?

According to gov.uk, heat is lost twice as fast through single glazing compared to standard double glazing, and around 7% of UK households have no double glazing.

Many period property homeowners are unaware that it is possible to double glaze new and existing sash windows.

As expert joiners, we can either:


Craft and install new double-glazed sashes into your existing box sash frames complete with draught seals and new cords. We can also repaint the existing timber in your chosen colour and fit a new set of ironmongery (if requested).


Craft and install a completely new double glazed sash window(s) including the box frame. We will remove the old window and replace with completely new double-glazed sashes housed in a new box frame.

Fear not, we know how important it is to retain the charm and originality of period homes and our professional joiners will carefully design and finish your windows as close to their origins as possible. We can even double glaze stained glass sashes.

Acoustic glass

This can also be double glazed for thermal performance, with an Argon-filled cavity and warm edge spacer between panes.

Laminated glass

This is held together with interlayers and won’t shatter if broken.

Toughened glass

Treated with heat, toughened glass is stronger than normal glazing so is less likely to break.

Vacuum insulated glazing

This is a premium glazing option that will offer you benefits greater than triple glazing but remain as slim as single glazing. This means it is an ideal option for period, listed and conservation properties, as its slim frame allows it to be easily retrofitted into existing box sash frames. It is approved by planning officers and boasts a U-Value of 0.7 (W/m²K) – that is A++ standard. The benefits of vacuum insulated glazing are unrivalled in terms of energy efficiency.

Draught proof your sash windows

Draught proofing your sash windows will ensure they are working efficiently and safely when you need them the most. Draught seals provide insulation for sash windows by preventing draughts entering your home through the perimeter of your windows. At Parsons Joinery, we regularly carry out a draught seal and overhaul service which includes the following repairs to improve a sash window’s performance:

  • Draught sealing
  • Improving insulation
  • Repairs to damaged or rotting timber and sills
  • Rebalancing and adjusting sashes within their frames
  • Installing new, modern (unbreakable) cords
  • Installing new retaining beads and draught excluders
  • Installing new locks and ironmongery

Our draught seal and overhaul process is detailed below:

1. Assess whether the windows are operating correctly and take note of any necessary repairs or improvements needed (i.e. One sash is dropping so it needs extra weight added).
2. Remove any existing ironmongery fittings.
3. Remove the existing staff bead.
4. Cut the cords of the bottom sash.
5. Remove the bottom sash and put to the side
6. Remove the existing parting bead.
7. Cut the cords of the top sash.
8. Remove the top sash and put to the side.
9. Take out the pockets to gain access to the weights, remove the weights.
10. Re-cord the box with new white nylon cords.
11. Attach the weights (and any additional weights if needed) to one end of the cords and place back inside the box
12. Hang the top sash back on to the new cords
13. Fit the new draught seal type parting bead.
14. Hang the bottom sash back on to the new cords.
15. Fit the new draught seal type staff bead.
16. Repair any demage caused by the installation process and prepare the new components for decoration.
17. Undercoat new components where necessary.
18. Install the new ironmongery fittings.

Use warm edge spacer bars

Warm edge spacer bars are components used in double or triple glazing window units. They are positioned around the perimeter of the insulating glass unit (IGU) to maintain the gap between the panes of glass. Unlike traditional aluminium spacer bars, warm edge spacer bars are made from materials that have lower thermal conductivity, which helps in reducing heat loss and improving the energy efficiency of windows.

The term “warm edge” refers to the fact that these spacer bars provide better insulation than traditional spacers, helping to keep the edges of the window warmer. This is important because the edges of a window are often the coldest parts and, if not properly insulated, they can lead to issues such as condensation, reduced energy efficiency, and even mould growth.

Window draught snakes

If your windows are draughty and you need an easy fixer, draught snakes are a great addition to your windows. Draught snakes are simple fabric tubes that you place underneath your window sill to prevent drafts from accessing your home. They are not a long-term solution, but they are effective at keeping draughts at bay on a particularly cold and windy winter night.

Repaint and seal your windows against the cold

If you have wooden sash windows, one of the most important things you can do to preserve the energy efficiency of your wooden windows is to protect the wood against rot and damage. To effectively seal your windows, strip off the old paint and sand the area thoroughly. Fill any holes in the wood with wood filler and then repaint the windows with an undercoat followed by a minimum of two paint coats. A quality paint job will help protect the wood from moisture damage. Resealing and repainting are all included within our draught seal and overhaul process as outlined earlier.

If you are unsure whether you need to repair or completely replace your sash or casement windows, our expert team can inspect and advise as necessary. There are no salespeople in our team, so the person who visits your property to inspect your sash windows and discuss your options will have the knowledge, skills and experience to offer you tailored advice. They can advise whether a sash window repair or draught seal may be an option, or whether a full replacement will be the most economical choice. Got a question about sash windows and the repair or replacement process?   Call us on 01273 814870 or email enquiries@parsonsjoinery.com.