Sash Window Double Glazing

Sash window with reduced heat loss diagram
Upgraded Sash Windows

We can upgrade your existing timber sash windows by fitting Planitherm double-glazed units.  Planitherm units provide an excellent thermal insulation solution for old windows.

The original timber window frame is sufficiently wide to accommodate new sliding sash windows manufactured to hold double-glazed units. We can manufacture sliding sashes in any appropriate softwood or hardwood, but recommend Accoya® because it is a modified sustainably sourced timber with a durability and stability that matches or exceeds the finest hardwoods.

U-Values and Energy Consumption

An upgraded Victorian sash window with double glazed units.
Victorian Bay with Upgraded Sash Windows

We always fit the most appropriate double-glazed units in order to maximise thermal efficiency.  For example, our 24 mm Planitherm units have a U-value of 1.2w/m2/k.  This provides a considerable improvement when compared with the 3mm (U-value = 6.8w/m2/k) and 4mm float glass types (U-value = 5.6 w/m2/k) that are usually fitted in old sash windows. (U-values represent the rate of heat transfer through glass. A lower U-value means that heat flows more slowly through the glass). Your exact energy consumption will depend upon the building, the local climate, and the interior temperature.

We always fit toughened safety glass in our new windows.  It makes economic sense to fit toughened glass to any new window because you are less likely to need to replace it during the lifetime of the window.

Spiral Balance Systems

An image advertising Accoya® high performance wood.
We recommend Accoya® timber

We replace sash cords and weights with a modern spiral balance system to offset the additional weight of the 14mm double-glazed units. The spiral balance system provides sufficient counterbalance to ensure the upgraded sash windows move effortlessly. To complete the package, we fit seals and brushes to your window frames, jambs and meeting rails in order to further reduce heat loss.

For more information about sash window upgrades please see our list of Frequently Asked Questions (FAQs) or use our contact form to email your query.