Customers often ask us about sash windows with double glazing. Can we double glaze old sash windows? Will double glazed windows eliminate condensation? What are the U-values of double glazed sash windows? Do you need planning permission?

We will discuss these questions and more in this article.

Timeless Sash Windows are a timber joinery refurbishing old windows and manufacturing new windows and doors. We have been in business for almost 50 years and are registered heritage contractors with the CIF in Ireland. Our specialist surveyors and craftspeople are experts in their field, trusted by architects and builders throughout Ireland and the UK.

Can you double glaze old sash windows?

Yes we can. The first step is to survey the windows to inspect their condition and measurements. In conservation areas, you will need planning permission or the help of a local architect to discuss the options for protected structures. 

One of our fitting crews will remove the sashes from the frames and take them back to our workshop in Co. Meath. Our specialist joiners remove the original (historically lead-based) paint, strip the sashes back to bare timber, splice in repairs and increase the rebate in order to house the thicker double glazed units. We will seal these in place and spray paint the sashes with 3 coats of Teknos specialist exterior joinery paint. Back on-site, the fitters will return the sashes to the refurbished frames, balance them with weights and touch-up paint if needed.

Will double-glazing eliminate condensation in sash windows?

Condensation occurs when warm air hits a cold surface, in this case, your windows. Using a dehumidifier (to remove moisture from the air), leaving windows slightly open or raising the temperature inside the property (warm air holds onto moisture better than cold air) are initial solutions. However, typically these are not cost-effective or practical long term.  Condensation can cause black mould on the timber frames, health complications and timber rot. We advise that you dry the glazing daily and wipe down the frames.

Double glazing is an effective solution as the thicker surfaces are warmer than single glazed. Thus providing improved insulation. The U-value is a measure of the heat retention of a window. Bear in mind that the glass on it’s own will have one value, and the entire window will have a different value depending on the insulating properties and construction of the frame, glazing bars and the seals.

What are the U-values for double glazed sash windows?

Each manufacturer will provide their own U-value specifications. With regard to the glass alone, he U-value of a 4mm single pane of glass is 5.7. The U-value of a 12mm double glazed Slimline unit is 1.9.

Our products are traditional designs in keeping with Victorian and Georgian styles and the U-values are dependent on the window chosen. Typically, the U-value for an energy rated sash window is 1.4.

Can you triple glaze sash windows?

Typically with wooden sash windows, triple glazing is not a viable option as the sashes become too heavy. However, if you are looking for the best windows with energy efficiency in mind, double glazed sash windows with draught sealing can achieve comparable U-values. Additionally, these windows maintain the slime and elegant aesthetics of traditional sash windows that add value to properties.

If you would like to find out more, or request a survey, contact us by phone 046-9023323 or email [email protected]. Alternatively, you can complete the contact form on our website here and we will be in touch.