Abstract: An insulation system utilizes a plurality of insulation fasteners to support an insulation board or the like adjacent the roof-supporting framework/purlins of a building. Each fastener comprises a clip member with projecting shank with the former engageable with a projecting flange of the purlin. Upon extension of the shank through or across an edge of an insulation board placed adjacent the building purlins, an underlying support washer is engageable with the shank so as to sandwich a portion of the insulation board or adjacent edges of adjacent boards therebetween. A plurality of insulation fasteners are used with each insulation board so as to support a plurality of insulation boards and overlying batt insulation adjacent the purlins and roof of the building.