U-Value Calculator for Timber Windows and Doors
We provide whole-window and whole-door U-value calculations for timber and wooden-framed windows and doors.
Our calculations are based on the dimensions, frame construction and glazing information supplied for the particular window or door. We calculate the thermal performance of the complete window or door, rather than simply using the U-value of the glass.
A detailed PDF U-value calculation certificate is provided showing the information used and the calculated result.
Our service is particularly suited to bespoke timber windows and doors, including hardwood, softwood and Accoya® frames, with double or triple glazing.
One-off calculations are welcome — no membership, subscription or minimum order is required.
No Membership / No Subscription
You do not need to subscribe or become a member to use our U-value calculation service.
There is no subscription, no membership fee and no minimum number of calculations.
You can order a single U-value calculation for one window or door, or use our service as often as you require.
We charge a flat fee for each calculation and provide the result as a detailed PDF U-value calculation certificate.
Whether you are a homeowner, joinery company, window manufacturer, architect, builder or installer, you can use our service whenever you need a U-value calculation.
What Our U Value Calculator Is Designed For
Our service provides whole-window and whole-door U-value calculations for timber and wooden-framed windows and doors.
The calculation takes account of the overall dimensions of the window or door, the frame, glazing area, glazing specification and other information supplied for the particular design. The result is a whole-element U-value, rather than simply the U-value of the glass.
Suitable for
Our calculations are based on the calculation principles of BS EN ISO 10077-1 and are prepared from the information supplied for the individual window or door.
A calculation for your window — not a manufacturer’s generic figure
Our service is not restricted to products from one manufacturer or proprietary window system. We calculate the U-value from the dimensions and thermal information provided for the particular window or door being considered.
This makes the service particularly useful where a Building Control officer, architect, builder or installer requires supporting U-value documentation for a bespoke timber window or door.
Scope of the standard calculation
Our calculation is intended for straightforward window and door configurations where the frame and glazing arrangement can be represented from the information requested on our submission form.
Some additional construction features can affect the thermal performance of a window or door and may require a more detailed calculation. These can include projecting sills or thresholds, frame extenders, dummy sashes, additional mullions or transoms, coupling components and other non-standard frame components.
If your window or door incorporates features of this type, please contact us before ordering a calculation so that we can confirm whether the particular configuration is within the scope of our service.
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.