One: the wall is never ready
The screen arrives on the date in the contract. The wall, the power, and the network are usually two weeks behind. That gap costs storage, a second mobilisation, and sometimes a crane rental. On one project the screen sat in a warehouse for 26 days because the plastering was late. Add 3 to 6 percent for schedule buffer.
Two: power is not where the drawing says
A 20 square metre indoor wall at 8 kg/m² needs a dedicated circuit. In retrofit buildings, the nearest available circuit is often 30 metres away. Conduit, cable, a breaker, and an electrician: 1 to 3 percent.
Three: the content does not exist
The screen is delivered and the client has a 1080p logo file and a PowerPoint. Someone has to build a 4K canvas, adapt the aspect ratio, and design for the viewing distance. That is a design fee, and it is often 2 to 5 percent. Budget it or the wall will show stretched files for a year.
Four: access equipment
A wall above 2.5 metres needs a lift or scaffolding. In a mall with a 10 pm access window, the rental is per night, not per day. We have seen a 4 percent line appear for a single night of scaffolding in a listed building.
Five: the disposal of the old screen
Nobody quotes removing the old wall, and the old wall is heavy glass and steel. In some cities it is classed as electronic waste and needs a licensed carrier. 1 to 2 percent, plus paperwork.
How to handle this in a budget
Add a 12 percent contingency line to the equipment total, and name it. Clients accept a named contingency; they resist a vague 'miscellaneous'. Our own quotes carry an assumptions page so these five items are visible before they become surprises.
The one that hurts most
Content. A screen with wrong content looks like a cheap screen. The client blames the hardware, the supplier blames the content, and nobody is wrong. Fix it in the budget at the start.