Make Your Home More Comfortable and Energy Efficient by Installing Slim Double Glazing Into Your Existing Period Windows

No more condensation problems or unwanted external noise. You will save money on your heating bills too.

“It is not often that I get blown away by a building product, but I find this absolutely extraordinary, looks like a single pane of glass.”


Slim Double Glazing for Period Windows

We have developed a unique process which allows us to install slim double glazed units into most existing single glazed sash windows and doors.

These advanced units are slim enough to be installed into most existing wooden frames, with minimal modification. This is just as effective as standard thickness modern double glazing and looks almost completely authentic.

Their cavities are filled with a mixture of krypton and xenon inert gases to enable them to achieve amazing  insulation values.

Combined with draught proofing, this solution will virtually eliminate internal condensation and completely transform the comfort and efficiency of your home.

Interested in finding out more? Give us a call, we’d love to chat.

Want more detail? Keep reading to learn more.

Why shouldn’t I just replace my windows?

Because our beloved Georgian, Victorian and Edwardian architecture is a valuable part of our national heritage. It can and should be preserved.

These properties are bursting with elegant features like cast iron fireplaces, hand crafted mouldings and ornate ceramic tile floors. So why sacrifice those charming sash windows? These can and should be preserved, and this no longer means having to forfeit the benefits of double glazing, usually even if you live in a listed property (please see our FAQ’s for more information).

Having your sash or casement windows replaced with timber replicas can also be up to twice as expensive, while the aesthetic sacrifice of UPVC is obvious and, in many cases, simply not an option.

Retaining your period home’s original character will make it more attractive to onlookers and buyers alike. Improving its energy efficiency and resistance to noise pollution with Slim Double Glazing will make it a drier, quieter, cosier place to live, while increasing its market value.


“Energy-efficient glazing reduces heat loss through windows and means fewer draughts and cold spots”

What about heat?

The rate of heat loss through a given material is known as its U-value: the lower the U-value, the better it is at preventing it. The average single glazed window has a U-value of around 5.6. Slim double glazed units range between 2.2 and 1.5, up to almost three quarters less, keeping you warm and saving you money.

What about noise?

Sound is measured in decibels (db) and a reduction of 10db represents a 50% cut in volume. A single glazed, unsealed window will offer less than 20db of noise reduction, whereas slim double glazed units carry a reduction rating of between 27db – 31db. This, combined with draught proofing, will cut the level of audible noise from outside by up to half, giving you the peace and quiet you need.

Will it really look authentic?

You will be hard pushed to tell the difference. At just 12mm thick, the units will be virtually undetectable. They look like single glazed windows, from inside and out. The units can be face puttied with traditional Linseed putty to give a truly traditional finish and can even be heat treated to give the glass a subtle warp, mimicking the hand blown look of yesteryear.

View a detailed specification of our Slim double glazed units.

What about condensation?

When warm air meets cold windows, you get condensation. This can cause a whole host of problems from wet window sills to rotten window frames, which can end up landing you with a hefty repair bill. A double glazed unit separates the cold outside from the warm inside, making condensation much less likely.

However, standard units can still suffer from condensation around the edges due to the conductive aluminium spacer in the middle, which transfers the cold temperatures. Our units are fitted with an ultra low conductivity, warm edge foam spacer, which ensures dry glass from corner to corner.

Can anyone have this done?

Generally speaking, yes.

If you live in a listed building You will need to contact your local conservation officer to find out. Read more here.

Most period frames are suitable and, where necessary, will be expertly restored by our experienced team, as part of the installation process. If not, they can be rebuilt to precisely match the originals.

Keen to protect your period home without compromising its appearance?

Happy customers

Client testimonials

Natasha, Maida Vale


"I used Envirosash to make 6 new sashes as well as an entirely new sash window. The windows are of the highest quality, beautifully made and draught-proofed. They keep the flat much warmer and we've already noticed how much quieter it is. Alex was competitive on price even taking into account the quality materials that he uses. I wouldn't hestitate to recommend Envirosash on the basis of their craftsmanship, reliability and general ease with which they performed the job."

Mervyn, Crouch End


"Alex was a pleasure to deal with and the job was done on time and as expected. His workforce did a high quality job and were always polite, helpful and attentive. They also made sure to clean up at the end of each day. We had most of the windows in the house replaced and it has made a real difference. Happy to recommend."

Sarah, Gravesend


"Had some replacement slim double glazed sashes fitted recently. Good craftsmanship and thorough job. Cleaned up every evening. Good to have a quote from someone who actually understands the work to be done, rather than from someone who is just a salesman. Would definitely recommend."

The Timber Window Specialist