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Upgrade Your Windows with Slimline Sash Replacement

Period timber sash windows are normally unable to accommodate double glazed units, and many planning authorities object to double glazing being installed in listed buildings and sensitive conservation areas in London and surrounding areas. Slimline double glazing is a viable alternative that is accepted by conservation officers in many cases. Sash Restoration London supplies and installs Slimline double glazed units, designed to fit existing timber sash windows. By using a smaller, gas-filled gap between the glass panes, slimline double glazed units can achieve an energy rating on par with standard double glazing. This makes them perfect for heritage buildings and period homes in London which need both the thermal benefits of energy efficiency and an authentic period appearance.

Slimline Glazing Features: 

  • Designed to replace single glazing in traditional box sash windows

  • Similar low U values to double glazing

  • In-keeping with traditional aesthetics

  • Ideal for listed buildings and conservation areas


We work closely with a number of local authorities and conservation officers to find the best solution for every property. If slimline double glazing is not approved, we can offer single glazing, secondary glazing and shutters.

Double Glazed Shutters: 


We can also manufacture and install ultra slimline double glazed shutters that provide high levels of insulation, whilst remaining sympathetic to the building’s original design. Our glazed shutters do not interfere with the normal sashes during winter and can fold away discreetly in the summer for a practical alternative to slim double glazing.

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.

What about heat loss? 


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. Slimline double glazed units range between 2.2 and 1.5, up to almost three quarters less, keeping you warm and saving you money.

Can anyone have this done? 


Generally speaking yes but if you live in a listed building you will need to contact your local conservation officer to find out. 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.

Contact us today to discuss your requirements with one of our helpful and friendly team. They are always on hand to answer any questions you may have and provide honest and impartial advice.​ Or for further information please contact us at: or call our head office on: 0207-6093012.

Sash Restoration London Team

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