Sash Restoration London
Head Office
Ripplevale Grove, 
Islington, London. 
N1 1HT
Tel:    0207-6093012
Mob: 07913372092
Sash Restoration St Albans
Hertfordshire Office
Blacksmiths Lane, 
St Albans. 
Tel:    0207-1646305
Mob: 07913372092 
Sash Restoration Reading
40 Wilton Road
RG30 2SS
Tel:    0207-1646305
Mob: 07913372092 

Slimline Double Glazing Windows for Conservation Areas

Period timber 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. 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 across London which are situated in conservation areas and need both the thermal benefits of energy efficiency and an authentic period appearance.

Slimline Glazing Window Features: 

  • Designed to replace single glazed windows in traditional box sash windows

  • Similar low U values to double glazing

  • In-keeping with traditional aesthetics

  • Ideal for listed buildings and properties in conservation areas


We work closely with a number of local authorities in London 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.

Slimline double glazing windows we have fitted in London:


Double Glazed Slimline 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 retention


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. Slimlite 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.

For further information or if you have any questions regarding our slimline double glazing windows please contact us at: or call our head office on: 0207-6093012