Timber frame single-glazing sash windows can be simply restored and reglazed with modern glazing solutions that greatly improve energy efficiency without the need to replace the entire sash window.
Older timber frame windows with single pane glazing can be upgraded by replacing only the existing glass panes. This is a cost-effective alternative to replacing the full window unit.
If you are thinking about where to restore or replace your sash windows, this article is for you.
Timber frame single-glazing windows can be simply reglazed
If your home has original timber frame windows with single glazing, you may be considering replacing them entirely for new double or triple-glazed windows to improve energy efficiency. However, a simpler and less costly option is to reglaze the existing windows with vacuum double glazing.
Reglazing involves removing the existing single glass panes and replacing them with new VIG custom-made double-glazing units. This can help improve the windows’ thermal performance and noise insulation dramatically.
The advantage of reglazing is that you can upgrade the energy efficiency of your existing timber windows at a fraction of the cost of complete window replacement. This maintains the original character and appearance of the windows.
Frames can be retained and restored if required.
An added benefit of reglazing is that the original window frames can often be retained and restored where needed.
If sections of the timber framing are found to be rotted or damaged, the affected parts can be cut out and new, matching timber spliced in. Any worn sash cords on sliding sash windows can also be replaced to get the sashes moving smoothly again.
With some basic repairs and maintenance to the frames, the existing windows can be restored to full working order.
This avoids the need to manufacture completely new window frames, retaining the traditional styling and original materials. Where the frames are structurally sound but weathered, they can also be stripped, sanded and repainted to refresh the timber.
Draught-proofing of original wooden windows
As well as installing new glazing, it’s advisable to draught-proof your original wooden window frames at the same time. Older windows can be prone to air leaks around frames, allowing heat to escape. Adding draught-proofing seals helps make windows more energy efficient.
Options for draught-proofing include:
- Applying self-adhesive foam or rubber strips around window sashes and frames. Compressible types allow the sash to still open and close freely.
- Installing brush or fin-type draught excluders within window sash channels. These seal the gap when closed.
- Fitting removable heavy curtains or installing secondary glazing over windows reduces air infiltration.
- Filling cracks and gaps in frames with mastic or caulk sealing.
- Fitting sash locks and sash window insulating kits to minimise air gaps.
New glazing that outperforms single glazing 8-12 times
When reglazing your timber windows, the best option for energy efficiency is to install vacuum-insulated glazing such as FINEO or Landvac rather than standard double glazing. This ultra-thin vacuum glazing has two panes of glass sealed together with a vacuum in between. The vacuum is a far better insulator than just air or gas between panes.
FINEO and Landvac vacuum glazed units offer thermal insulation up to 8-12 times better than single glazing. This is because there is virtually no convection or conduction through the vacuum, minimising heat transfer. They insulate 2-3 times better than conventional double glazing as well. The slim double-glazed vacuum units are only 6-8mm thick so they can directly replace existing single-glazing in heritage frames.
Vacuum glazing provides excellent thermal insulation and noise reduction for your home. Going for the highest performance units will maximise energy savings on your heating bills compared to basic double glazing. The extra cost of vacuum units is recouped over time in the form of lower energy costs.
How much does it cost to double-glaze an existing sash window?
If you’re considering reglazing your existing sash windows with double-glazed units, expect costs in the region of £700 – £1200 per window depending on the size. This covers the installation of new energy-efficient double-glazed units into the original sash frames, including new glazing compound/putty and labour.
Additional costs of around £500-£700 per window would apply if your window frames need sanding, repairs and repainting at the same time. This would involve stripping back the frame, splicing any new timber, repairing cords/sashes and repainting for a full frame refurbishment along with the new double-glazed units.
For a typical Victorian terraced house, you may be looking at a total cost of £6000-£8000 to reglaze all the sash windows including frame restoration work. Installing slimline vacuum-glazed units will be at the upper end of this range.
What are the different types of double-glazing glass?
When choosing new double-glazed units for your reglazing project, there are several glazing options to consider:
- Standard double glazing – This has two panes of glass sealed with an air gap in between. Typical U-values range from 2.7 to 3.3 W/m2K.
- Low-E double glazing – A transparent coating is applied to the glass to reflect heat back into the room. Argon or krypton gas fills the gap, improving insulation. U-values range from 1.4 to 2.2 W/m2K.
- Vacuum glazing – Two panes of glass are sealed together with a vacuum for superior insulation. Examples are Fineo and Landvac units with U-values from 0.7 down to 0.2 W/m2K.
The lower the U-value, the better the thermal efficiency. Double-glazed vacuum units like Fineo offer by far the best insulation.
