Every building requires some sort of ventilation and it is a building regulation requirement to provide a certain level of background ventilation in certain rooms or areas within your home.
Background ventilation can be achieved through small slot vents which are placed in to the head of our frames. The amount of ventilation required would be determined by the size and type of room and whether it was in a new build or an extension/alteration.
Trickle vents aren't the only method of providing this ventilation, this can also be achieved through heat recovery systems, air bricks or vents placed in the fabric of the building.
Your architect and building control should be able to advise how much building ventilation is required.