Briary toolsuite
The thermal transmittance of a complete window, frame and glass together, calculated to BS EN ISO 10077-1:2017 with the conventions of BR 443 (2019) and checked against Approved Document L Volume 1, 2026 edition. Confirm the applicable edition and transitional arrangements for your project before relying on those checks.
Say how many lights the window has across and up, then work on the elevation itself. Click a light to change what it is, drag a mullion to move it, right-click anything to edit it or apply the same value everywhere. The drawing redraws as you go.
Build a project of windows, copy one to make the next, and keep them together in a single file you can save and reopen here as a single project file.
Every area, every heat-flow term and the source of every value, downloaded directly as a PDF with a verification code so a reader can confirm the report matches the inputs it came from.
Using the right window dimensions. Where the 2026 edition applies, paragraph 3.2 of Approved Document L Volume 1 sets out hot-box measurement or calculation using the actual window size and configuration for new dwellings. Paragraph 3.3 identifies the frame sections, sills, add-ons and other components that should be accounted for. Paragraph 3.4 sets out the options for existing dwellings, including reference-window calculations.
Publication does not make the 2026 edition applicable to every current project. It takes effect on 24 March 2027, or 24 September 2027 for higher-risk building work, subject to transitional arrangements. Confirm the project's regulatory route before selecting the evidence and dimensions to use.
Centre-pane glazing values are calculated to BS EN 673:2024 and frame data is reduced by Annex F of BS EN ISO 10077-2:2017+A1:2025. The same engine drives the Briary desktop software and both are held to the same published conformance vectors.
Your drawing is built in the browser. Geometry and thermal values are sent to the server for calculation; reports also use the project context you supply. When you save or produce a report, any supplied company, assessor, client, project name and reference are retained securely by Briary, separately from anonymous Tool Insights. Calculation values, notes, files and passwords are not retained by this activity facility. Read our tool privacy information.
This tool calculates transmission heat loss only. It excludes solar gain, air leakage and condensation risk, all of which clause 1 of BS EN ISO 10077-1:2017 places outside the scope of the method.
The result is only as good as the frame and junction data entered. For a Building Regulations submission, the frame U-value and the frame-to-glazing linear thermal transmittance must come from a numerical calculation to BS EN ISO 10077-2 or from a hot box test. BR 443 (2019) section 11.1 restricts the default tables built into the tool to energy calculations. The tool says so on screen and in the report whenever a default has been used.
Window Energy Ratings and Doorset Energy Ratings are not calculated. Those follow the Glass and Glazing Federation Glazing Manual Data Sheet 2.3.
Start here, then keep the guide open alongside your work. Expand a section for the information you need.
Have overall window dimensions, the frame system, glazing information and supporting thermal-value sources ready. This tool calculates the whole window rather than the glass alone. Read the standard, conventions, project context and edition limitations displayed on the explanation page and in the report. A whole-window result is not a whole-building compliance assessment.
Open the calculator and complete Project information, including the appropriate work context. Add an identifiable window reference. The assessor’s name is required for a PDF; organisation is optional. You can develop the drawing before completing report details. Keep notes of assumptions and the source of any supplier information.
Set the overall dimensions and the arrangement of lights across and up. Work on the elevation: select a light to edit it, and use mullions and transoms to describe the actual frame arrangement. Check units before entering dimensions. Examples are a starting point to learn the controls, not approved specifications for your project.
Review each frame side and internal frame component, the glazing assigned to each light and the relevant junction values. Record where thermal inputs came from. Glass Ug and whole-window Uw are different values. If you use a built-in/default value, read the stated limitations and confirm that it represents the actual system. Do not replace supplier evidence with an attractive result.
A schedule usually repeats one construction at several sizes, so Duplicate opens a dialog with a row per new window: reference, width, height and quantity, with Add another size for as many rows as you need. Every copy keeps the frames, glazing, sashes, bars and shutters, and because mullion and transom positions are held in absolute millimetres they move in proportion to the new size — a centre mullion stays centred, and an off-centre one keeps its proportion. Revisit size, frame arrangement and specification on every copy afterwards: a wider opening may need a different frame section, and a larger pane may need thicker glass, which changes its U-value. Select each window and inspect its result, warnings, drawing and take-off; a successful calculation for one window does not validate the rest.
The result combines the entered glazing, frame and junction contributions. Review warnings and the detailed breakdown before selecting Download PDF. If the assessor name is missing, the tool will explain this and take you to Project. Server or geometry errors are displayed with a recovery route. A result outside the selected limit is not corrected by downloading its report.
Save project creates a .bwu project file containing the editable project. Open it later to continue; a PDF cannot be reopened as a design file. If a request fails, save the project first, check the displayed error, and retry when your connection is available. Do not repeatedly change valid thermal inputs to resolve a connection problem.
The in-tool Guide explains drawing controls, selection, frame and glazing editing, defaults, saving and reports. Use it alongside this operating guide. For problems, email toolsuite@briary.co.uk with the tool name, browser, window reference, exact error and reproduction steps. Read the privacy information before sharing files or generating reports; omit unnecessary client information from support emails.
Send the location, project stage and current drawings. We will confirm the assessment route and information needed.