The plan take-off

The plan take-off is where Thermly measures your building. You trace walls, roofs and floors off the calibrated plan, drop windows, doors and skylights onto the elements they belong to, and assign each shape to an assembly. The result is a measured, checkable set of areas and a marked-up diagram that goes into your report.

This is the workflow that sets Thermly apart from typing areas into a form: the geometry is explicit, openings net out automatically, pitch is applied to roofs, and every number traces back to something you can see on the drawing.

Prerequisite: upload and calibrate the plan first.

The toolbar

The tools across the top of the mark-up canvas:

Tool	What it does
Select	Select, move, edit or delete a shape; click a placed opening to edit its size.
Zone	Trace an area by clicking its corners; double-click to close. For roofs, floors, and gross wall faces.
Rectangle	Draw a rectangular zone from two opposite corners.
Line	Trace a wall run by clicking along it; length × stud height gives the wall area. Walls only.
Opening	Drop a window or door on a wall, then enter its width × height. Walls only.
Skylight	Drop a skylight on a roof, then enter its size. Roofs only.
Text	Place a text label on the diagram.

The toolbar shows the tools that apply to the element you are taking off - Line and Opening appear for walls, Skylight for roofs. Beside the tools sits the scale cluster: Scale and H×V scale set the scale from a known dimension (see calibration).

Other controls: Snap (with per-source options: points, intersections, plan lines, grid), Angle lock (constrain lines to 0 / 45 / 90°; hold Shift to invert it momentarily) with a Screen / Relative angle-reference toggle, Pan, zoom (with a fit-to-view toggle), Lens (magnify under the cursor), m2 Measures (show area and length readouts), and Undo / Redo. A second, contextual row sits under the toolbar: it names the active tool and holds its options (the opening Type, the line-width and colour pickers, the roof pitch) plus a hint telling you what the tool expects. For a roof zone the hint reads: "Click the roof-plane corners, double-click to close, then set the Roof pitch here so the sloped area is right."

Walls

Select the Line tool and click along each wall run, double-clicking to finish. Thermly multiplies the run length by the stud height to get the gross wall area. Trace the gross face; you cut the openings out next.

Raking walls

A gable end, a wall under a mono-pitch roof, or any wall whose stud height changes along its length is a raking wall - length × a single stud height would get its area wrong. For these, start from the wall's element row on the H1 page with 📐 Trace raking wall (instead of ✏️ Draw on plan and the Line tool).

Draw on a side-on elevation (a plan sheet or elevation that shows the wall's true profile), not the floor plan. Outline the wall's shape by clicking its corners and double-clicking to close, exactly as you would a zone. Thermly takes the wall area straight from the traced polygon, so a sloping or stepped top edge is measured as-drawn - there is no stud-height multiply. A traced wall carries a 📐 Raking profile badge so you can tell it apart from a length-based wall run at a glance.

Everything else works the same: assign it an assembly with Paint as, and drop windows and doors on it with the Opening tool - they net out of the raking wall just as they do a rectangular one.

Roofs and ceilings

Select Zone, click the roof-plane corners, and double-click to close. Then set the Roof pitch, either in degrees or as a rise:run (for example, 3:12). Thermly converts the plan footprint to the true sloped area (roof area = plan area ÷ cos(pitch)); a flat default under-counts a pitched roof. The measurement label shows both the sloped and plan areas, for example "45.50 m² ∠30° (plan 39.40 m²)", so the conversion is auditable.

Floors

Trace the floor with Zone or Rectangle. For a slab-on-ground or a proprietary raft, the floor's R-value comes from a wizard rather than a layer stack - see Supplied floors and rafts.

Openings: windows and doors

With the Opening tool, choose Window or Door, then click the wall to drop it. Enter its width × height in the inline panel; a live readout shows the area in square metres. Each opening is subtracted from the wall it sits on - the wall's element row shows the net area - so your net wall area is correct without separate arithmetic. Openings carry an auto tag (W1, D2, and so on) that you can edit to match the plan's numbering, and an optional name.

You can also cut an opening out of a zone by drawing it: with a zone selected, use Cut as to trace a window, door or void polygon inside it. The zone's label shows the deduction, for example "32.40 m² − 2 openings · 24.00 m".

Windows and doors stay within the wall envelope as glazing and door area: Thermly nets them from the opaque wall and counts them in the glazing and door buckets of the heat-loss check.

Skylights

With the Skylight tool, click the roof and enter the skylight's true in-plane size (the sloped width × height, not pitch-corrected). Skylights net out of the roof and roll into the roof-plus-skylight bucket of the reference calculation. Skylight R-values get specific treatment under Appendix D - see How Thermly calculates compliance.

Assign each shape to an assembly

A traced shape becomes an element only when it has an assembly. Use the shape's Paint as selector to assign one - a sample assembly to start, or one you have built. The shape takes on the assembly's colour and appears in the diagram legend by that name.

Keyboard-driven drawing

The take-off is built to be driven fast from the keyboard. While drawing a line or zone: arrow keys aim the next segment, type digits to set an exact length, Tab switches to entering a bearing, U toggles mm / m, Enter places or closes, Backspace undoes the last point, Esc cancels. In Select, arrow keys nudge (Shift for a larger step) and Delete removes. See the full list under Keyboard shortcuts, or press the ⌨ Shortcuts button on the canvas.

Legend and saving

Thermly builds a legend from your assigned shapes (assembly name and colour); drag it to reposition it, adjust its size, font and visibility from the toolbar's Legend menu, and set your starting defaults in Settings → Plan markup. Click Save diagram to embed the marked-up plan in your report. Re-open and revise it any time.

Next

• Give your elements real build-ups: Assemblies and products.
• See the numbers it produces: Reading the H1 report.