An improved apparatus and method for accumulating sheets having a horizontal transport deck. Inserts are fed from an insert feeder positioned above the deck. Driven accumulator nip rollers are positioned to receive accumulations of sheets transported on the horizontal deck, and they are also positioned close enough to the insert feeder to receive inserts fed from the insert feeder. A recessed accumulation deck is positioned immediately downstream of the accumulator nip rollers. When a first sheet rests in the recessed accumulation deck, a subsequent second sheet will be placed on top of the first sheet when it enters the recessed deck. The process is controlled whereby insert sheets are released by the insert feeder prior to arrival of an accumulation on the deck. The released insert is driven by the accumulator nip rollers onto the recessed accumulator deck. Then when the accumulation arrives, it is deposited on top of the insert resting there.