Defective Roofing Screed

Screed refers to the final layer of whatever is on top of the roof...that is to say, if you have a roof made of concrete beams or panels, then a screed goes over the top of this so that there are no gaps, the screed is usually sand and cement or even thin concrete....it can be anywhere from 25 to 100mm thick.

Defective means it's going to rain in.

If a roofer has told you that the screed is defective on your flat roof, then it probably is...if you think you are being conned, get a second opinion and/or take a look yourself...if it were mine and it was feasable, I'd put a pitched roof over the top