Do your windows and doors measure up to today's tough performance tests?

Do your windows and doors measure up to today’s tough performance tests?

Sliding Sash Window Close Up

Why performance tests - such as acoustic testing - on your windows and doors are vital for building regulation compliance and attracting potential buyers.

Thorough testing of windows and doors by the appropriate bodies doesn’t come cheap. For this reason, not all companies will go through the official channels, and generic testing is used to generate the numbers and figures they know you want to hear. Others will even guess their results.

There is no substitute for full and independent testing in a UKAS accredited laboratory to assess the standards required for full compliance with UK building regulations and global standards.

Do I really need this? Absolutely.

Guesstimates and generic figures will invalidate certification for building regulation compliance – which could be a problem down the line, particularly if you want to sell your house or make an insurance claim. Solicitors have a habit of picking up on these details.

made to measure doors

What kind of testing?


Unless your doors and windows are certified as PAS 24 compliant, even if they are multi-point locking, then you cannot be sure that they are up to the job of keeping unwanted intruders out.

So what is PAS 24? The Publicly Available Specification (PAS) is a minimum performance standard expected of doors and windows as set out by Part Q building regulations. Doors and windows undergo testing by a United Kingdom Accreditation Service (UKAS) certification body. They are put through rigorous testing where the windows and doors are put through a human and mechanical hardware attack test that lasts for a duration of 15 minutes. They are also tested for their ability to withstand weather conditions.

Tests are undertaken in strict laboratory conditions and following the test, the Certification Body will regularly visit the production facility from time to time and intermittently re-test products to ensure that the products still perform to PAS 24 standards.

PAS 24 offers a minimum standard and ideally you are looking for windows and doors that exceed this standard for true peace of mind.

Internal shot of a legacy sliding sash window



U-values are the measurement of a material’s efficiency which ensures it’s keeping your heating in. The lower the U-value, the more efficient your window or door is.

This means:

⦁ Lower heating bills – more money for you
⦁ Lower carbon footprint – a better planet for everyone
⦁ You feel good for being environmentally responsible
⦁ You’ll have a more comfortable home

U-value measurements also vary depending on what part of the window is being measured.

Be aware – You might see products advertised for their centre pane U-value which is usually better than the whole product-value, simply because all windows experience more heat loss around the edges.


Westbury white timber casement windows

How low should I go?

In 2018 Part L building regulations for replacement products stipulate a whole unit value maximum of 1.6 or lower for windows and 1.8 for doors. Good products will outperform these guideline values.

All windows complying with building regulations will perform to a level that prevents heat loss and lowers the environmental impact. But don’t be swayed by U-values alone – windows that compete on U-values by a margin of 0.1 or 0.2 under the regulation threshold won’t make any discernible difference to your bills or your carbon footprint.

At Westbury we produce windows that have a whole product U-value of 1.1W/m2K based on three-layer 4mm thick glass with a centre pane value of 0.6W/m2K. This is achieved in part through our use of Accoya, which has extremely low thermal conductivity, coupled with specially formulated bonds and strong joints.

Westbury door leaves are 68mm deep and therefore can incorporate a much thicker and wider choice of energy efficient and sound reducing glass. These facts enable Westbury to offer independently tested and authorised energy saving doors with excellent whole product U-Values of 1.4W/m2K and under.

windows performance tests - box sash windows

Acoustic testing

The quiet life doesn’t have to be the stuff of dreams; with today’s advances in technology you really can shut the sounds and stresses of modern living out of your home if you have the right windows and doors and this is particularly important for people living in busy urban areas. But how do you measure this?

Acoustic performance is measured using the Weighted Sound Reduction Index (Rw). This generates a number that rates the effectiveness of a material or system. Increasing the Rw by one point means a reduction of 1 decibel in noise level. The higher the Rw number, the better the sound insulation.

The following test results demonstrate the Rw of various Westbury products in accordance with BS EN ISO 10140-2:2010; the British Standard European Norm for measuring the level of sound insulation of building elements.

Each result is followed in brackets by an adjustment (C,Ctr) these are figures you deduct for an accurate reduction index of pink noise (C) (random low-frequency noise) and traffic noise (Ctr).

Product type acoustic test result
Casement window       …………. Acoustic test result 38 (-1;-4)
Box sash window         …………. Acoustic test result 35 (-1;-2)
Lower spec glass, box sash window:   …………. Acoustic test result 33 (-1;-3)
Spring balanced sash window:    …………. Acoustic test result 36 (-1;-3)
French door:             …………. Acoustic test result 38 (-1;-4)


This video demonstrates the acoustic tests being carried out on Westbury’s windows and doors. The results show that we perform just as well as our industry competitors, and better when it comes to traffic noise testing.

The acoustic test results of our French doors are impressive compared to industry standards. Owing to the opening gaps and ironmongery of French doors, it is particularly difficult to achieve good noise reduction performance.

So there you have it – don’t be sold on price – make sure you buy into windows and doors that measure up – and be sure to check who’s doing the measuring!