Submit Window / Door details

Our u-value calculator is intended for use with bespoke timber framed windows and doors.

To calculate a u-value in accordance with Part L of the Building Regulations we need the information as specified below.

  • The size of the frame. Length and Width

  • What is the Frame made from

  • How thick the frame is

  • The glass that is being used
  • What spacer is being used

Submit that information to us using the form on this page.

u-value for timber framed wood window and doors


All measurements are to be specified in m.
L1 and W1 are the dimensions of the Frame.
L2 and W2 are dimensions of first glass panel, if there are more than one glass panel continue filling in the boxes. L3 and W3 are for the second panel and so on.

Glazing Types

The glass types specified are manufactured by “Saint Gobain”. Double and Triple glazing. For Example 4mm / Air / 4mm means a double glazed unit with 4mm thick glass, then Air then another 4mm thick glass.

Note: If your glass is supplied by any other manufacturer please specify the details in the appropriate box alongwith the u-value of that glass, which you can obtain from your supplier.

Glazing Space

This is the space between the glass panels. In the previous example it is “Air”, and that space could be between 6mm and 20mm.

Type of Sealant used

We will assume foam. However if something else is being used please feel free to specify what it is..


The normal spacer used between the glass panels is made of Aluminium, however the “Swiss Spacer” is more efficient, and will lower the overall u-value. There are other types of spacers available and these should be listed here.

The Cost

Our U Value Calculator is designed to give accurate u-values for windows and doors. A Detailed certificate with a unique serial number, which should be acceptable to building control, will be issued in PDF format on receipt of full payment.

The cost of this service is £35 per certificate.
Payment by bank transfer to (Starling Bank)
Account Number 74111522
Sort Code 60-83-71
Reference Your Company Name.

Or by using Paypal using the link below.