We present a model for the design of multiproduct sequential batch plants extended with parallel production lines. This model is meant to support strategic capacity decisions and is formulated as a MILP model. First, we introduce the concept of parallel production lines as a new design option into existing plant design models. Then, we optimise the number of production lines, their design and the product assignment to the installed lines by minimising capital costs of the equipment. Furthermore, we extend the objective function with startup and contamination costs and study the influence of these costs on the chosen plant design options. We find the presence of parallel production lines beneficial as not all products have to share all equipment anymore. Moreover, we show that the incorporation of operating costs affects volume-wise asset utilisation per batch. An example to illustrate the applicability of our model is presented. (C) 2016 Elsevier Ltd. All rights reserved.