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Double glazed sash windows. A buyers guide

Double glazed sash windows: A buyers guide.

Sash windows have been an iconic look for many older buildings and in recent years have seen a comeback in popularity. The standard sash window has many double glazed sash windows benefits over a hinged window, primarily as a space saver, but also a much more traditional look. Sash windows do not need to be expensive to upgrade to double glazing, as well as reducing draft from poorly fitting or worn frames. In addition, modern designs can allow for a range of opening styles which older frames were unable to offer. For example, the bottom section can be mounted on a series of hinges offering two different ways to open:

We will focus on the different options available in upgrading to double glazing for your sash windows. However, first, we should look at the benefits of moving to double glazing and improving the frames of older windows.


Single vs. double glazed

Many properties in the UK still have traditional single-glazed sash windows. Despite how nice they look, they are a real weakness when it comes to heat loss. Single glazing is not as energy efficient as there is no barrier between the internal heat and the outside cold. This results in heat being lost through windows much more quickly than through brickwork as there is a much thinner barrier. Double glazing is an effective way to reduce this as there are two panes of glass (double the thickness already!) and a thin layer of inert gas (usually argon) between the panes. This acts as an insulator and keeps more heat in the home, reducing energy bills and increasing energy efficiency. Rooms will warm up quicker when you turn the heating on and stay warmer for longer.

The other consideration is the age of the window frame. Many old frames utilised a pulley system, built into the frame, to help lift the lower pane and keep it in place. Over time this causes wear on the mechanism and on the wooden frame itself. Added to this potentially some rotting of the wood, the frame itself will not fit as effectively and cause drafts. Not only is cold air getting into the home, which isn’t pleasant, but warm air is escaping causing you to heat the cold draughts that used to come around the edges of the old windows should be a thing of the past.


Upgrading an existing sash window

To begin with, it may be worthwhile to consider if refurbishing your existing sashes is a viable option. If they are “too far gone” then you may have no choice but to replace them. However, if the wood is in decent condition and it’s just a matter of functionality or upgrading to double glazing there are ways to do this that can be very cost effective.

Adding internal secondary glazing is an option that has been successfully used many times in many homes. The approximate cost to fit secondary double glazed panels on the interior of a sash window can start around the £200 to £250 per square metre mark. This method will give you the benefits of double glazing with a much reduced cost and without the hassle of replacing the whole frame. However, this may be a temporary measure in older windows as the frame may not have a huge amount of ‘life’ left and will need to be regularly checked for damage and rot.


Replacement of a sash window

In cases where the window frame is not in good condition, or if you just want to update the look of your home, then a full replacement if the best option. Whilst this is more expensive than upgrading existing sash windows, in the long term this can be a much better option and you have more choice available for the style, design and materials used.


Materials – uPVC sash double glazed windows 

Sash windows As with any double glazed window you can opt for a uPVC sash window. When you choose uPVC sash windows for your period property window replacement you get a wealth of benefits compared to timber. They include:

  • Low maintenance – Gone are the days of the sanding down and re-painting involved with real wood. With only the occasional wipe down, uPVC windows will stay looking like new for years to come.
  • Durability – Modern uPVC is extremely durable. Whereas timber can be compromised by rot and insect infestation, uPVC provides a durable and weather resistant finish to protect your home.
  • Cost-effectiveness – Traditional timber is expensive. When it comes to budgeting, uPVC windows are always the most cost-effective option.

For many people, they opt for uPVC simply because it is cheaper. In fact, you can replace a wooden sash for a uPVC equivalent for about £750, while a like-for-like timber replacement may cost nearer £1350.


Materials – Timber

However, timber window frames tend to last a lot longer and uPVC can fade and become discoloured by UV rays. The fact is that most people are looking to replace their original timber windows, from properties built in the late 19th or early 20th century. This demonstrates that if correctly looked after, wooden sash windows can last. The fact is though, in order for them to last this long they do require regular maintenance – if the frame lacks paint or varnish, the wood will begin to rot very quickly. Also make sure if you do decide to go for timber sash you choose hardwood windows since these are the ones that will last!

uPVC double glazing will not last nearly as long – in terms of lifespan, many glazing companies offer a 10-year guarantee on their uPVC window frames. The lifetime of a uPVC has been set at 35 years by BRE (the building research company), but still this is far less than the timber frame windows (provided they are maintained correctly). Having said that, they do require very little maintenance over their lifespan.

The choice you make may come down to cost, but companies specialising in sash windows will be able to create most designs and styles in wood and uPVC. If your budget can stretch to a timber frame then this will last a lot longer if maintained, but it is recommended to check that the wood has been sourced ethically.


Other Points to note

Estate agents often come out with the classic line ‘properties with timber frame windows look better and sell for more.’ Well, in some cases that is true but like many things, beauty is in the eye of the beholder. The truth is that good uPVC windows look very similar to the wooden sash windows – but this really does come down to a personal preference.

Some properties in certain areas of the UK will have restrictions on the type of changes that you can make to the appearance of (and the material used to replace) new windows. For example, if you live in a listed building or are located in an AONB (Area of Outstanding Natural Beauty,) there could easily be local restrictions in force. If you are unsure, please check with your local planning department before doing anything.