Assessing Quality Wooden Windows

The general quality of wooden windows sold in the UK is certainly not the best. So, to help people make an informed choice on what to look for, we want to focus on the questions that you should be asking and how to spot a high quality timber window.
Of course, price is often a key concern. But many people don’t realise that poor quality windows may only last 6-7 years, and an increased cost is saving you so much in the long-term. To make things more difficult, the price paid is not a rock-solid guarantee of quality timber either.
Most windows look great in the brochure, and are most likely nice when they arrive. But a self-destructive time bomb of deterioration lurks in the poor quality of the materials used to manufacture.
I’m continually dismayed to see how many UK consumers are duped into buying both timber and composite windows with really low quality softwood timber. Windows should not be made from any other type of timber other than dense slow-grown heartwood.

Many consumers are also duped into thinking the aluminium skin of a composite window is a perfect impenetrable protection. This is certainly not true if the timber behind this is not of a joinery standard.

How do the Germans do it

In Germany and Denmark, government run technology institutes DICTATE to factories how they MUST make their window products and the minimum standards to which they must abide.
We do have kite marks and ISO standards in this country, but these do not properly govern the quality of the components going to make the product. UK quality standards usually only require products to be made consistently.

Know what you are looking at

The picture you see below is from one of our European factories and shows a 75mmx75mm end-on piece of timber, which has a density of 550 kg/m3 at ambient 12% moisture content.

High Density Slow Grown Nordic Pine quality wooden windows

Growth rings are very tight, and the timber is much harder and denser than the timber you would normally see sold off the shelf in UK timber merchants.
A dense timber’s natural tendency to absorb moisture is low. This is super important and why our high quality wooden windows are only made from quality timber like this.
Compare this timber to a well known UK window manufacturer, whose timber density is 220-280 kg/ m3. Not quite balsa wood, but the timber has a high propensity to absorb moisture.
Timber does naturally absorb and expel moisture. And the degree to which it does so is directly related to the timber density.

Why is this so important I hear you say?

When timber absorbs moisture it expands. Have you ever had to put your shoulder into a window to open it, or had a window that sticks badly?
Dry Timber, from which your home is constructed, usually has a moisture content of 6-16%. It feels entirely dry to the touch and, during the seasons, the timber breathes: expelling or absorbing moisture depending on the natural humidity of the air around it.
When moisture content in timber goes above 20%, the fungus that causes wet rot can start to become active.
The timber also expands up to approximately 7% depending on the moisture content; this is a common cause of sticking or jammed windows.
Very few people maintain their windows properly with the recommended repainting regime. A small fissure in the paint can let moisture into the timber.
Windows made from dense timber are your insurance policy – so that if moisture does get in, then the timber’s natural tendency to act like a sponge is significantly reduced.

So, when buying quality wooden windows:

Ensure that you find out:

What is the timber density used in manufacture? We suggest that it should be a minimum of 400 kg/m3
Is it truly slow grown heartwood? At a recent UK Homebuilding show, I posed as a customer as one salesman tried to tell me that, because the timber they used was FSC, this was a sign of its quality! Certainly a sign of its origins, but definitely not of its quality or density.
Is the face timber knot free? This is important too, as knots are often areas where the defects start to show and where problems can start. Quality wooden windows should be guaranteed to be knot-free.
If the window has excessive joints and timber junctions on the external weather face, then again take this as an indication of likely poor quality.