Deducting openings without double counting
14 October 2026
Openings are where hand take-off quietly goes wrong. The same door has to come out of the brickwork, out of the plaster on both faces, and out of the painting, and each of those is usually measured by a different person on a different day.
In QTac you mark the opening once.
Mark the opening
Trace the door or window with the Area tool (A), exactly as you would any other shape. It does not need to be assigned to an item; it only needs to exist.
Point the items at it
When you assign a wall or a plaster face, the Assign window lists the traced areas on that sheet. Tick the ones that belong to it. From then on that opening is deducted from that item, in full.
What the dimension sheet shows
The deduction is its own row under the item, with its own working, so the QS sees the gross, the deduction and the net. Nothing is silently netted off.
| Row | What it shows |
|---|---|
| Gross | the measured face, with its working |
| Less opening | the marked area, with its working |
| Total | what goes to the Summary |
Reveals and jambs
QTac does not add jamb plaster automatically, because whether you measure it depends on your own convention and on the specification. If you want it, measure the reveal as a length and assign it to a plaster item in the usual way; it appears as its own row, where a checker can see it.
A negative total is allowed
If you deduct more than you measured, QTac shows a negative total rather than hiding it or refusing. That is deliberate: a negative figure is a loud signal that something is wrong, and you will see it immediately in the Quantities tab.