In this communication, an attempt has been made to define and evaluate the solar fraction (F-n) for a north wall on the basis of annual experimental studies. An even-span greenhouse has been considered for experimental studies for the climatic conditions of Delhi. Experiments were conducted from September 1999 to August 2000, A model based on Auto-CAD 2000 has also been developed for validation. It has been observed that the solar fraction mainly depends on angle of incidence, solar altitude angle and shape and size of the greenhouse. It is inferred that solar fraction (F-n) plays a significant role in thermal modelling of an even-span type greenhouse. Further, it was noted that there is a fair agreement between experimental and theoretical results. Copyright (C) 2002 John Wiley Sons, Ltd.