Double Glazed Sash Windows


Upgrade to Double Glazed Sash Windows

Retain the heat and 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.


We’re consistently rated ‘Excellent’ by our amazing customers

A small selection of double glazed sash windows we have manufactured and installed

Bespoke new slim double glazed sash windows by Ventrolla
Slim Double Glazed Sash Windows
Double glazing installed in 1900's cottage
Double-glazed sash windows Edinburgh home
sash window double glazing
Double glazed timber bay window
6 over 6 double glazed sash windows installed
Slim double glazing units

One of the most common questions we get asked is “Can I double glaze my existing Wooden sash windows?” sometimes phrased as “Can I add double glazing to original sash windows?”


When did double glazing take hold in Britain?

The 1970’s, if you can remember it you weren’t really there. Or was that the 60’s. Either way it was during the age of space hoppers, power cuts, thick luxuriant moustaches and a farm boy called Luke fighting an empire when double glazing made its way across the Atlantic Ocean from the US to us.
Although this new window technology had been around since the 1950’s in America, the price and lack or regulation meant there was little to no adoption over here in Blighty. The introduction of much stricter energy efficiency legislation coupled with the oil crisis and massively inflated fuel costs meant the British were ready to embrace the bill reducing benefits of double glazing and the trend has only increased with the modern iterations becoming incredibly efficient at reducing heat loss and helping to quiet the outside world.

What actually is double glazing, what makes it better than single glazing?

Even though glass itself is classed as an insulator, with a single pane separating the outside air 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 which actually mostly acts to reduce noise intrusion. The magic happens in-between. The gap is filled with a clear, odourless and non-toxic gas from the Noble family on the periodic table which are excellent insulators. What that means is the warm air on one side is isolated and doesn’t lose its heat to the outside world.

Ok, so can you come and install the units in my original timber sashes?

We’d love to but there is a problem. If you look at your windows, you’ll see the horizontal pieces of wood, the glazing bars, in which the panes are installed are pretty thin. They were designed to hold a single pane of delicate glass. A modern double-glazed unit is thick and heavy and simply wouldn’t be able to fit in or be supported by the thin timber that makes up the glazing bars (sometimes called Muntins).

Right, well I’ll just go rip them out and replace the whole thing with a big white plastic window!

WAIT! Please don’t do that. If you care about the authenticity and kerb appeal of your home keep reading.

So tell me how you can install double glazed sash windows in my home.

What we can do is craft new, bespoke beautiful sash windows from the finest timber that exactly match your homes’ existing style. They can be installed in your window box frame and will look like they came with the house when it was built and you will be able to relax in a warm, quiet, (from outside noise, we can’t do anything about your kids) comfortable home that retains its period character.

How do you manage to make a unit slim enough not to look out of place?

The gap in between the two panes is where all the thermal efficiencies are gained. When filled with a Nobel gas heat from one side finds it very difficult to transfer energy across. There are two main gasses used. Argon and Krypton, no relation to Superman [EDIT] I’ve just been told that Superman’s home world of Krypton was named after the gas which means “Unknown”. So now you know!
Argon is the cheaper gas and is 6 times denser than air. Krypton on the other hand, is 12 times as dense as air which, although it is more expensive, allows us to create the same thermal barrier as a thicker unit filed with Argon and thus make a specially designed slim, unobtrusive unit made for classic properties built in the Georgian, Victorian and Edwardian eras. 

I get the best of both worlds then?

Absolutely. You get to retain the 19th century charm and character while benefiting from 21st century heat and noise performance. And, like a 2am QVC special, that’s not all you get, all our new double glazed sash windows come fitted with our unique and patented draught-proofing system which can stop winds up to 71mph (that’s touching on Hurricane speeds) entering your home.

Sounds great, I wish I’d known about this earlier.

Well we have been around for over 35 years. Get in touch with us today and upgrade your timber sash windows with the most beautiful double glazing you’ll ever see. Or won’t see!


We’ve developed a modern sash window that not only looks beautiful, but is drastically more energy efficient.


Replacement sashes help to minimise the disruption and cost of redecorating - reducing the overall cost of the work.


All of our new double glazed sash windows comply with Part L of the Building Regulations.


  • Reduced energy costs
  • Up to 30% improvement in energy efficiency
  • Slim discreet double glazed sashes
  • Easy future maintenance
  • 5 Year Guarantee


Replacement Sashes 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


DESIGNED FOR peace of mind

Whether it’s our 5 year guarantee or the fact that both our replacement and new double glazed sash windows can withstand 71 mph winds, Ventrolla’s solutions are designed to delight. What’s more, our new double glazed windows come with a FENSA certificate for added peace of mind.