In the light of energy reduction, transitional spaces are recognised as ways to receive natural light and fresh air. This paper analyses the effects of courtyard and atrium as two types of transitional spaces on heating demand and thermal comfort of a Dutch low-rise dwelling, at current and future climate in 2050. The inclusion of a courtyard within a reference Dutch terraced dwelling showed an increase in annual heating energy demand and a decrease in the number of discomfort hours. In contrast, covering the courtyard and making an atrium led to reduction in the heating demand but more discomfort hours. Results showed that using a courtyard in May through October and covering that (as an atrium) for the rest of the year is the most efficient situation in the Netherlands