U-Value Calculator for Timber Windows and Doors
Our U-Value calculator is a whole window calculator designed to accurately calculate the thermal performance of timber and wooden framed windows and doors. This calculated value conforms with Part 1 of standard BS EN ISO 10077 Thermal performance of windows, doors and shutters.
We can advise on how you might achieve the required standard. A U-value calculated by us should be sufficient to satisfy the requirements of Building Regulations.
Our calculator is primarily intended for use with wooden windows and doors. These can be made from hardwood or softwood, of any size with double or triple glazing. If you can provide us with the r-value of any other type of frame you are using we can provide a u-value for that too. Our u-value calculator is not restricted to products manufactured by one company.
No Membership / No Subscription
You do not to subscribe to our website. You do not need to be a member of our site and there is no minimum number of u-value calculations that you need to submit in any given period.
You can use our services for a one off calculation, or as many times as you require. We charge a flat rate fee for carrying out the calculation and sending you the result on a pdf certificate.
What Our U Value Calculator Is Designed For
How our U Value Calculator Works
The calculator evaluates frame material, glazing configuration, spacer type, and dimensions to provide an accurate U-value. Timber frames are handled specially to reflect real-world performance, unlike generic calculators.
Timber vs Aluminium vs PVC
Timber (Wooden Frames):
Timber is naturally insulating and can improve thermal performance. However, U-values for timber windows and doors vary depending on species, frame thickness, profile geometry, and glazing interface. Timber frames require a specialist U-value calculator to ensure accurate results and regulatory compliance.
Aluminium Frames:
Aluminium conducts heat efficiently, so frames without thermal breaks can reduce energy efficiency. Modern aluminium windows use thermal breaks and multi-chamber frames. Accurate calculations must account for these differences in the frame details.
PVC (uPVC) Frames:
PVC frames have predictable thermal performance due to a multi-chamber construction. While easier to model than timber or aluminium, accurate results still require precise data from the frame and glazing.
Why Material Choice Matters:
A reliable U-value calculator models each frame material correctly. Treating timber, aluminium, and PVC the same can produce inaccurate results. Our calculator focuses on timber windows and doors, where material choice and frame construction can significantly affect U-values.
When a U-Value Certificate Is Required
A U-value certificate provides formal evidence of thermal performance, and is often required for:
Indicative calculations are fine for early-stage planning, but final approval often requires a certified calculation carried out according to the standards specified in BS EN ISO 10077.
Who Needs a U-Value Certificate
Certification is typically required by professionals involved in design, manufacture, or installation of windows and doors:
Certification is particularly critical for timber windows and doors, where material and construction details significantly influence thermal performance.