Double Glazed Windows

Double Glazed Sash Windows

Choose Double Glazed Sash Windows

Retain the heat & style by upgrading your original wooden sash windows with slim double glazing.

Double glazed sash windows allow you to keep the traditional charm and beauty of your wooden windows while also benefiting from modern energy performance. We offer two double glazed sash window solutions; replacement slimline timber secondary glazing installed into your existing sash box (window frame) and completely new wooden double glazed windows.

Whether you opt for replacement sashes or new windows, our expert workshop will tailor-make your units and incorporate our unique Ventrolla Perimeter Sealing System (VPSS), designed to virtually eliminate draughts, leaks and rattles.

Energy-efficient, yet packed with traditional charm, our industry-leading double glazing for sash windows lets you have it all. We’ve designed a slim unit that performs just like those found in uPVC windows, yet it retains the original profile and beauty of a timber sash.

How does double glazing work?


Even though glass itself is classed as an insulator, with a single pane separating the outside and inside air, any warmth in your room is going to be whipped away by a cold window.

Double glazing works by adding a second pane of glass. The gap between the layers of glass are filled with an inert gas like Krypton, an excellent insulator, and separates the warm air inside your home from the cold air outside of your home. 

Can I add double glazing to my original sash windows?


If you look at your windows you’ll notice that the glazing bars that the panes are positioned between are relatively slim. They were designed to hold a single pane of delicate glass. The increased depth of a modern double glazed unit means that it’s larger and heavier, and simply wouldn’t fit in, or be supported by, the original timber glazing bars.

How do I install double glazed sash windows in my home?

We can craft made-to-measure double glazed sashes and fit them into your existing window box frame retaining the integrity of your period windows, while making your home as comfortable as possible.


Our double glazing specification

Double glazing specification

Slim 14mm (4/6/4) double glazed units, Planitherm Total+ glass (outer pane) and krypton filled cavity. Centre Pane U-Value of 1.5 Wm²K and Total Window U-Value of 1.8 Wm²K

New Window Double glazing specification

Slim 16mm (4/8/4) double glazed units, Planitherm Total+ glass (outer pane) and krypton filled cavity. Centre Pane U-Value of 1.2 Wm²K and Total Window U-Value of 1.5 Wm²K

Draught proofing

Our draught proofing system, the Ventrolla Perimeter Sealing System (VPSS) is fitted on all new joinery, as standard

Energy efficiencies

Reduced energy costs and up to 30% improvement in energy efficiency thanks to the same draught-proofing, Ventrolla Perimeter Sealing System (VPSS) used on our single pane windows


Complies with Part L of the Building Regulations, although it's worth noting that replacement sashes (not full new windows) is outside of Building Control