Should I buy timber sash windows or uPVC sash windows?

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.

We have an enormous number of clients who are interested in replacing their windows, but we always get asked the same question – should they opt for timber sash replacements or uPVC sash replacements. In this blog we are going to look at the pros and cons of both to help shape your decision.

Reducing heat loss

The first thing to say is that replacing single glazing with double glazing will immediately increase the comfort of your home. Rooms will warm up quicker when you turn the heating on and the cold draughts that used to come around the edges of the old windows should be a thing of the past.

U-values for windows are as follows (remember lower is better!)

    • Single glazed sash window will have a u-value of about 5.1 W/m2K
    • Re-glaze existing sash windows + draught proofing will equal 2.1 W/m2K
    • New box sash timber windows double glazed will be about 1.7 W/m2K
    • New box sash uPVC windows double glazed will be about 1.6 W/m2K

Now these are approximate U-values, if you decided to go for high efficiency glass, the U-value can drop as low as 1.2 W/m2k. In fact, if you opt for triple glazing this can fall even further to 0.9 W/m2k.


You also might wonder why re-glazing existing sash windows gives a slightly higher U-value even though they are double glazed. This is for two reasons:

    1. The distance between the two panes of glass tends to be minimal

    2. New double glazing units normally always have an inert gas (e.g Argon) between the two panes that helps further improve their energy efficiency – this is almost impossible to achieve when re-glazing existing windows.

So based on the fact that wood pretty much matches uPVC on efficiency, we need to consider the other factors at play here.

Cost of wooden sash versus uPVC sash windows

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.

On the whole, people have a lot of glazing on their homes, especially in Victorian properties where sash windows are prevalent. You can almost replace two windows with uPVC for the cost of replacing one with wood. This massive price difference is in our opinion the key decision maker for most people when it comes to replacing their windows.

Lifespan of uPVC/timber sash windows

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, including Anglian glazing, 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.

uPVC frames also used to be known to discolour as a result of UV. In the last 10 years the uPVC companies have resolved this using by manufacturing UV stabilised frames. Most glazing companies should now offer a guarantee against ‘profile discolouration’.

The look of uPVC versus timber sash

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. Some people may put real value on windows, while others may be more bothered about the proportions of the rooms, for example.

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.

Regardless of whether you opt for timber frame or uPVC – always go FENSA!

The final point worth mentioning is regarding FENSA (Fenestration Self-Assessment Scheme).  This was set up in response to building regulations for double glazing companies in England and Wales.

If a glazing company is registered with FENSA, you can be sure that the windows you are installing properly adhere to building regulations. Please make sure therefore that any glazing company you use are FENSA registered!

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