Elevation take-off: cladding, render, deducting openings and voids not deducted

This guide follows French practice: French standards (NF DTU), French regulations and French bill conventions. Most sources are in French.

Elevation items and their units

Render, cladding and external wall insulation share the same basis: a wall area from which the openings are (or are not) deducted. Around that area come lengths, often more expensive per metre than you might think.

Workmanship standards, such as NF DTU 41.2 for external timber cladding or NF DTU 42.1 for façade renovation with waterproof coatings in France, say how to carry out the work. For the take-off, the rule that applies is that of the contract documents: the specification and the bill format define the unit, what it includes and the threshold for deducting openings. Read them before you start.

Measuring on the plan or on the elevation

Two methods complement each other:

• On the floor plan, you take the length of the elevation and multiply it by the height. It is quick for straight elevations of constant height.
• On the elevation, you draw the wall area directly, with its gables, steps and openings. It is essential as soon as the height varies.

On the plan, measure the outer face of the finished wall, not the wall centre line. On a 10 × 8 m house with 20 cm walls, the perimeter measured on the centre line is 0.80 m shorter than the outer perimeter: almost 4.5 m² forgotten over a height of 5.60 m.

Which height?

The height is taken between two reference points that must be written down: from finished ground level, or from the top of the plinth, to the eaves, the parapet or the underside of the coping. The plinth is often a separate item, with another finish and another rate. Gables add a triangle above the eaves; its height equals half the gable width multiplied by the roof pitch.

Deducting openings: voids not deducted

An elevation pierced with openings needs less render or cladding, but more work around each opening: stops, returns, reveals, sills. Contracts settle this in two ways:

• Openings deducted. The area of each opening, width × height, is taken off, and reveals and soffits are paid separately, per linear metre or per m² of girth.
• Voids not deducted. Openings smaller than a threshold set by the contract, in m² per opening, are not deducted. The area counted in excess pays for the work around the opening, whose reveals are then generally not paid on top.

The threshold applies opening by opening, never to the total of the openings in an elevation. There is no universal value: two packages of the same project can have different ones. Note the one you apply at the head of your take-off.

Reveals

The reveal is the return between the face of the wall and the window or door frame. For a deducted opening, its girth is two heights plus the width of the head (the soffit); the sill or flashing is counted separately, per linear metre. Multiplied by the reveal depth, this girth gives an area, if the contract asks for it in m². With external wall insulation, these returns need special cuts and profiles: they have their own line.

Scaffolding

Scaffolding is measured on the length of elevation actually scaffolded, multiplied by the scaffold height, without deducting openings: it covers the whole elevation. Corners, brackets, protection (netting, sheeting) and hire period are separate items in most scaffolders' quotations; follow their breakdown rather than inventing one.

Cladding and external insulation: the items around the area

Cladding is not just its boards. Depending on the specification, the framing (battens or rails), the breather membrane, any insulation and the insect mesh at the base are included in the rate per m² or itemised separately. External and internal corners, top and bottom stops, reveal linings and junctions with the roof are counted per linear metre. With external wall insulation, the base profile follows the foot of the wall and the insulation thickness increases the reveal depth: measure it before working out their area.

Worked example

South elevation of a house: 10.40 m long on the finished face, 5.60 m high from finished ground level to the eaves. The specification requires openings of 1.00 m² and over to be deducted (threshold taken for the example).

If all openings were deducted, WC window included, the net area would drop to 47.48 m², and its 2.10 ml of reveals would be added. The east gable is measured on the elevation: 8.00 m wide and the same eaves height, roof at 40%. Rectangle: 8.00 × 5.60 = 44.80 m²; triangle: 8.00 × 1.60 / 2 = 6.40 m² (the apex rises 4.00 × 0.40 = 1.60 m); that is 51.20 m² gross, before its own openings.

The most common mistakes

• A length taken on the wall centre line rather than the finished outer face.
• Gables forgotten, or measured as rectangles.
• A plinth counted with the elevation when it has its own item.
• A threshold applied to the whole elevation rather than to each opening.
• Openings deducted and reveals forgotten, or the reverse.
• A window deducted over the full height of the elevation in a measurement on plan.
• Elevations not kept apart: impossible afterwards to answer “how much on the north elevation?” or to phase the work.

Doing it in Kotelys

• On the plan, the Length tool follows the outer face; with a height given to the type, Kotelys writes the wall area: “10.40 ml × 5.60 m = 58.24 m²”.
• Each opening is placed on the line with its own height (door, window, full height or a value you enter): only its width × height is taken off.
• The type's “Openings not deducted below … m²” setting applies the rule for voids not deducted: small openings stay counted, and the take-off calculations say so.
• On the elevation, the Area tool draws the wall and the gables, with one deduction per opening to take off. The perimeter of each area is written in the calculations and in Excel.
• Sills, copings and corners are drawn as Lengths; grilles and downpipes are counted with the Count tool.
• One zone per elevation (north, south, east, west) or per block: the reports give the quantities elevation by elevation.
• The PDF take-off calculations write the gross area, each opening (“− Opening 1: 1.20 × 1.25”) and the net; the Excel workbook repeats the object-by-object detail.

Reveals are still yours to calculate: Kotelys gives the width and height of each opening in the take-off calculations, from which their girth follows.

Further reading: elevation take-off in Kotelys, and the other guides.

Sources

1. FFB, « Publication du nouveau NF DTU 41.2 » (external timber cladding)
2. FFB, « Réfection de façades par revêtements d'imperméabilité : le NF DTU 42.1 illustré »
3. Éduscol STI, CAP MPI 2021 technical file: example of a specification setting the method of measurement

Thresholds and values described as “taken for the example” are not rules: those of your contract (specification, bill of quantities) always prevail.