Why openings are measured over
The rule looks inequitable at first. A window means less masonry and is nonetheless paid for.
The reason lies in pricing. An opening reduces material consumption but considerably increases labour: corners must be formed, profiles set, material cut, lintels built in, junctions made. Measuring over is the flat compensation for that additional labour.
The rule thereby replaces item-by-item payment for the extra work with a quantity allowance. Without it, every reveal, corner and junction would have to be tendered and measured as its own item.
The thresholds differ by trade
This is where most errors arise. There is not one threshold but several.
| Threshold | Trades |
|---|---|
| deduct above 2.50 m² individual size | masonry, concrete including formwork, drylining, rendering and plasterwork, external insulation systems, joinery, painting, wallpapering |
| deduct above 0.10 m² individual size | tiling, screeds, floor coverings |
The difference between 2.50 and 0.10 square metres is a factor of 25. Transferring the shell trades' rule to a floor covering produces a substantially wrong result.
Three refinements belong with this, and each of them is regularly overlooked. They concern the reference size, the direction of the threshold and the governing dimension.
| Refinement | What follows |
|---|---|
| What governs is the individual size | not the sum of all openings in an area; two windows of 2.0 m² each are both measured over although together they exceed the threshold |
| The threshold is an upper limit for measuring over | openings up to and including 2.50 m² are measured over, so one of exactly 2.50 m² is measured over |
| The smallest dimensions govern | where a reveal has a rebate, the narrowest dimension applies rather than the outer one |
A worked example
An internal wall of 5.00 by 2.75 metres contains a door. Two door widths lead to entirely different accounts.
| Case | Opening dimensions | Area | Treatment |
|---|---|---|---|
| Single door | 1.01 × 2.13 m | 2.15 m² | measured over, no deduction |
| Double door | 1.50 × 2.13 m | 3.19 m² | deducted |
The wall area is 13.75 square metres. The first case invoices 13.75 square metres, the second 10.55. At an identical unit rate the two accounts differ by more than a fifth, and the difference rests on twelve centimetres of door width.
That is not an arithmetic error but the system. Where the opening is deducted, the additional work on the reveal is separately payable; where it is measured over, it sits within the area price.
Recesses, lintels and abutting elements
Alongside openings the ATV govern further cases, and they follow a different logic. What governs there is partly the tender rather than the geometry.
| Element | Treatment |
|---|---|
| Recess with a separate item | deducted, regardless of its size |
| Recess without a separate item | billed with the wall item, no deduction |
| Lintels and shutter boxes | measured over in masonry work and charged separately, regardless of size |
| Abutting elements | taken into account from around 0.5 m², below that measured over |
The recess rule is notable because it makes the treatment depend on the tender rather than on the geometry. Providing a recess item therefore also changes how the wall item is billed.
The precise values and wording sit in section 5 of the relevant ATV and must be read there. The reading order is covered in the article on reading the ATV.
What applies to connected areas
A recurring point of dispute concerns full-height openings and adjoining areas. It arises at every passage between two rooms.
According to a decision of the competent review body, applying the thresholds does not depend on whether the areas concerned have any material connection to one another. Full-height openings below the threshold are also measured over under several ATV.
Where a recess extends partly into adjoining areas measured separately, the proportionate recess area is used to determine the amount measured over. The threshold is therefore tested per area and not for the opening as a whole.
The rule does not apply as a matter of course to private clients
This is the most important point of this article and the least often stated. It concerns not the size of the quantity but whether the rule applies at all.
The deduction rules presuppose that the VOB/B, and with it the VOB/C, have become part of the contract. Between construction businesses that is customary and reflects a widespread trade usage.
Towards a private client who did not themselves propose applying the VOB, applicability is not self-evident. A client from outside the construction industry need not know a measurement rule under which what was not built is paid for.
A clear recommendation follows: on contracts with private clients, incorporating the VOB belongs expressly agreed and the effect of the deduction rules explained. An account confronting the client with this system for the first time creates a dispute that was avoidable.
Incorporation is covered in the article on agreeing the VOB/B. It also sets out the stricter requirements applying towards consumers.
What follows for pricing
Three consequences arise for daily work. They concern the quantity, the price and the check.
| Consequence | What follows |
|---|---|
| The quantity follows the ATV, not the geometry | an area derived from a model or drawing becomes the contractual quantity only once the deduction rules have been applied |
| The unit rate depends on the deduction treatment | an item whose openings are measured over carries the reveal work in the area rate; the same rate with openings deducted is too low |
| Checking begins with the ATV for the trade | only where it is silent does the general rule of DIN 18299 apply |
Related articles
This article reflects the position of the standards at the date of checking and serves professional orientation. The amounts and dimensions used are worked examples. It does not constitute legal advice and does not replace assessment of the individual case.