Flattage or flats are timber frames covered in canvas, plywood or hardboard and painted. Flats are used as scenery because they are relatively cheap to make, being of wood and canvas with the painting providing the design, and because they are easy to store - when leant against a wall in the wings they take up little space.
Examples of flats can be seen in Serafino Brizzi’s Designs for Stage Scenery. The section with the door centre-stage would have comprised a three-dimensional truck, but the wall to the stage-left of it would have been made using of two flats.
In Brizzi’s Interior of a Gothic Fortress, the offstage sections of wall were almost certainly flats, whilst the onstage sections under the arches would have been trucks.
Flats remain upright by an angled brace hinged from the back and anchored by stage weights. They are secured together by cleat lines. A cleat line is the name for a length of rope that is tied around a metal or wooden hook known as a cleat. Each flat has typically three or four cleats along each vertical edge and the line is run from the top cleat of one flat to the second down on the adjacent flat to the third down on the first flat and so on until adjacent flats are flush and secure.
Cleating a flat is one of the many skills needed by the stage crew. As the cleats (hooks) start at the top of the flat the line must first be thrown so it loops the top cleat. It is then thrown again in the opposite direction so it loops the second cleat on the adjacent flat without it unravelling from the first and so on.
Another skill required of stage crew is the running (moving) of flats. The height of a flat obviously varies according to its function, but an illustration of how difficult they can be to move is provided by the scenic flats at the London Coliseum which are typically 8 centimetres deep by 8 metres tall.