From 2003 to 2006 a study of church roofs in Val d'Oise was performed within the framework of SDAVO to to outline the development of structures and techniques of carpentry from 11^th to 20^th century. 150 roofs were observed, from all periods, with particular emphasis on those that most typified each type and period. If several unknown Romanesque roofs were discovered, the rest belong to a relatively known repertoire. There are a large number of Gothic roofs of the first third of 13^th century (12% of the corpus) and for the most part unpublished. Several of them show a perfect mastery of 'fermes et pannes' (bent and purlins) towards 1230 and of its widespread nature in the religious architecture in Ile-de-France in this period, to the detriment of 'chevrons-formant-fermes' (common rafters forming a bent) which survive until 16^th century only for their vaulting. The post-medieval roofs betray a drop in the quality of wood used, which accompanied the loss of carpentry skills at the beginning of 20^th century.