Which? Trusted Installer

What is a U-Value?

14th February 2014

Find an Installer

Keep Your U-Value Low and Save Money

If you are in the process of researching house extensions, you will need to understand the importance of U-values. This term describes how much heat loss is involved in any type of building element, such as a window, wall, floor or a roof. 

In basic terms, a U-value measures how well particular parts of a building can transfer heat. By researching the best double-glazing products as part of your investigations into house extensions, you can make a fully informed buying decision.

A low U-Value indicates a material is good for retaining heat; but, if it loses heat, then it has a high U-Value. House extensions built using thermally-efficient products will, therefore, produce a much lower and cost-efficient score.

Why U-Values?

The idea behind using U-Values is to keep carbon emissions low, reducing energy bills and ensuring that buildings produce a more comfortable living or working environment.

U-Values are assessed for their energy performance by the Government’s Standard Assessment Procedure (SAP) and maximum U-Values are set out during the design process of the building.

How U-Values are Calculated for House Extensions and Other Buildings

Depending on the thermal resistance of the building materials used, and the thickness of each layer, this forms the basis of the equation that enables the thermal conductivity of each layer to be calculated.

A U-Value is measured as W/m2K. This means the amount of energy in watts that travels through one square metre of material, for every 1-degree difference in temperature between the inside and the outside.

When researching house extensions, bear in mind that the U-Values of a single glazed window with a wooden or PVC-U frame are generally higher than those of a solid brick wall or a standard 30 degrees pitched roof. 

House extensions that are insulated can benefit from U-values that are reduced by around two thirds, which is why so many homeowners are now deciding to insulate their cavity walls or get their loft insulated. 

What U-Values Mean for House Extensions

Lower Costs

Choosing double glazed windows or insulating roofs for conservatories or house extensions can lead to a lower U-Value. It is worth taking the time to explore which materials have a lower U-value so that you can reduce the amount of heat loss and overall heating costs of your home.

Lower U-values equate to lower costs. House extensions, conservatories and orangeries that are thermally efficient rely less on heating systems to retain warmth, which means they can stay warm organically – allowing the thermostat to be dialled down during colder weather. 

Better Comfort

Conservaglass – a high-performing glazing used in all Ultraframe products – blocks out up to 83% of solar rays that means its house extensions, conservatories and orangeries never get too hot during summer and spring and will prevent warm air escaping at all other times.


House extensions that have been fitted with high-performing glass – and the right combination of double glazing products – will produce a lower carbon footprint that will reduce a given home’s impact on the environment and make it more ecologically friendly.

Extensive Research

Ultraframe continues to heavily invest in new technology that will make its customers’ homes more energy efficient and, therefore, cost-effective to run. We also rigorously test our existing products to ensure that they deliver the right levels of performance.

Staying Cool Matters as Well

House extensions also need to be well-ventilated. During warmer periods, it's important to keep air circulating – otherwise, condensation could form and turn to mould. 

A range of ventilation options are available and as follows:

  • Trickle vents. They encourage convection and filter out warm air before it can land on a cool surface and form moisture.
  • Roof vents. These can be manually operated via a dedicated spindle or fitted with sensors that react to rain and temperature.
  • Doors. Choosing doors that open almost fully – like bi-folds – will invite in lots of cool air that will keep your climate well-balanced.
  • Fans. House extensions fitted with fans benefit from the air that’s constantly circulating and an attractive decorative element.

Talk to Your Nearest Ultra Installer

Begin a conversation with one of our approved Ultra Installers today by using our free search tool. They will be able to tell you about Ultraframe products that’ll help keep your U-value as low as possible. 

Submit a request to us at the end of the search process to benefit from further contact from our team. We will be able to call you with more information about our house extensions, conservatories and related products.

Related Articles

11th July 2018
Kitchen Extension Ideas

Kitchen extension ideas that will make your home lighter and brighter, while giving you the extra space you need.

Design FAQs
8th May 2018
Three Design Options for Your Bungalow Extension

The only limit is your imagination when you design your bungalow extension with Ultraframe.

Design FAQs
8th May 2018
Garden Room Extensions: Everything You Need to Know

Build a glass extension that matches superb aesthetics with market-leading performance. Find the inspiration you need right here.

Design FAQs
8th May 2018
Explore Our Orangery Extensions Range and Feel Inspired

Contemporary or traditional orangery? Read our short design guide for inspiration.

Design FAQs
18th December 2018
Modular Extensions

Click to find out more about modular extensions, and see if they're the right product for you!

Planning Building FAQs Regulations

Get A Free, Tailored Quote

Got your heart set on your next home improvement? Get in touch and we'll offer you a bespoke price.

Request A Quote

Download Our Brochure

Take a moment to relax and browse through our brochure, it's an easy way to see our full product range.

Download Brochure
Find an Installer Start Your
Download Brochure View Virtual Tours