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Insulating Period Windows

A staggering 38% of British homes were built prior to World War II, with well over 9 million homes built before 1900. With the average house having 10-12 windows that’s a lot of glass. Of all those windows a very large majority have sadly been replaced, often with uPVC double glazing, due to poor maintenance, inadequate insulation properties or even just fashion trends. Traditional single glazed windows have a bad reputation when it comes to heat loss and thermal resistance, otherwise known as U-value. With the world focussing on climate change and ecological regulations the future hangs in the balance for many of Britain’s remaining ‘original’ windows.

However, replacement of the original windows can have more than just a stylistic impact. Having windows which match your home’s architectural style is well known to increase the value of your property. By removing the authentic windows from your home, you could actually be costing yourself money. Furthermore, if you are lucky enough to live in one of Britain’s 400,000 listed buildings, installing new doubling glazing probably isn’t an option.

[Below – Original Crittall windows on 1920’s architecture]

[ Above left – Single glazed original 18th century casements in a Devon thatch. Above right – Iron framed 17th century cottage windows ]

As single glazed windows will always be the ‘thinnest’ part of your home, and are generally thermally inefficient, draughty, provide little security and have poor acoustic performance, how can you live in a period property and stay warm, cosy and secure?

Below is a brief guide to making the most of your home’s ultimate original feature;

Good maintenance

Primarily keeping your wooden or metal windows in tip top condition is paramount to their functionality. This includes addressing any issues effecting the stone, brick or render surrounds and sills. Water ingress from neglected windows is the number one reason the units might fail. Good habits like keeping the glass free from condensation, addressing cracked glass quickly, touching up any damaged putty and repainting frames with good quality linseed oil based paint every 5 years should be undertaken to increase the life of your windows. Condensation is inevitable with single glazed windows and modern living but damage from prolonged damp is generally a lifestyle issue. Windows should preferably be trickle vented, left open a crack at regular intervals and not over-sealed to allow some minimal airflow. Investing in a good quality window vacuum used daily when condensation occurs can save many hours of future restoration. Often windows are removed because they are considered beyond repair, however, if you have a minimum of 30% left of your timber windows there are many specialist joiners and sash window experts that can restore them to their former glory and may even be more cost effective than replacement.

[ Above left – Well maintained door and leaded lights that have survived for a century. Above right – An example early of social housing with rare original windows still in situ ]

Thermally lined curtains and blinds

Good quality fabrics and soft furnishings can make all the difference to the warmth and acoustics of the period home. Adding thermal linings to your window dressings is a quick and cost-effective way of reducing heat loss. Adding door curtains and draft excluder ‘sausages’ in winter can allow your home to breathe whilst helping to keep it toasty warm. Thermal linings that hang behind your existing curtains can be purchased ready made from many furnishing retailers, or custom made if your windows are irregularly sized. Similarly, Roman blinds can be purchased ‘off the peg’ or made to measure. Alternatively blinds and curtains can be assembled with thermal interlining built in. Fabrics with thermal properties are barely thicker than standard furnishing fabrics and so style and design of curtains and blinds is not compromised. Additionally, thermally insulated window dressings will also help keep your rooms cool in summer. In the centuries before the generalised use of central heating it was also quite usual for curtains to be added to internal doors and four poster beds, adding extra insulation and privacy, although this is not always a practical solution in modern homes. However, the addition of curtains or ‘portieres’ on exterior doors is often over looked and yet can make a huge difference to heat loss. Fitting a clever device known as a Portiere rod will enable the door to be opened and closed without drawing back the curtain.

[ Above left – A Portier Rod allows easy access, Above right – Roman blinds combined with thermally lines curtains creating a cosy space ]


A less fussy but equally attractive solution to keeping your home cosy may be to have wooden shutters fitted. Historically shutters were a very important part of every window although they became less popular through the 20th century after central heating became the norm. However apart from just the increased thermal properties, shutters have other added benefits.

[ Above left – External shutters on a Cornish fisherman’s cottage. Above right – Contemporary internal shutters for a traditional look ]

External shutters, still popular across much of Europe, also help to protect the window from the weather, for example during storms, freezing temperatures or baking hot sun, protecting the delicate frame from deterioration. Putting operable exterior shutters on your single glazed windows can make huge gains in energy efficiency, keeping the cold winter wind off the glass and cutting down on both condensation and heat loss, whilst providing added security, especially at ground floor level.

[ Left - Contemporary plantations shutters compliment the sash windows on this Victorian terrace property ]

However, fitting exterior shutters is not always possible, may not be practical or does not suit always the aesthetic. This cottagey twee-ness is another reason for their fall in popularity. Interior shutters on the other hand have experienced quite a revival in popularity in the 21st century with the fitting of slatted plantations shutters offering style, light and privacy, plus they can upgrade the energy performance of your windows. Angling the slats upward during the winter and downward in the summer keeps the heat where it belongs.

Secondary glazing

With the thoughtful retrofitting of discreet secondary glazing, all the performance elements can be improved, and in most cases is fully accepted by the conservation officer as a reversible adaption. With careful designing the original windows remain unaltered and aesthetically uncompromised. This makes secondary glazing the perfect option for listed buildings and conservation areas. Energy efficiency can be improved by over 70% whilst, very importantly, still allowing the building to breathe. There are may options available to suit all types of window and budget, and the units can be surprisingly discreet.

[ Above left – Discreet secondary glazing on neo-gothic leaded windows.

Above right – A patented specialist system on a large Georgian sash window ]

Advances in technology has enabled products such as acrylic plexiglass systems to become available to the general public as well as for conservation and heritage projects, where as glass units have become lighter and more slimline. The cost of such glazing systems can be recouped by the increased energy efficiency and reduction in heating bills, resulting in better U-value scores and EPC ratings for your home. As well as the financial & economic benefits, secondary glazing will also improve the acoustic performance by eliminating external noise such as road traffic. Added to all this, the security of your home is also improved as secondary glazing is a strong deterrent for the opportunist. Such an installation would be wisely considered in order to maintain the integrity and value of any period property.

At ArchiWest we are very passionate about original features and with conservation close to our hearts, we always consider the building’s heritage in our design concepts. Contact us if you would like further information about how we can help you with your project. - 01934 311017


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