A method of manufacturing roofing shingles is provided. The method includes the step of coating a continuously supplied shingle mat with roofing asphalt to make an asphalt-coated sheet. The asphalt-coated sheet has at least one prime portion and at least one headlap portion. The thickness of the asphalt-coated sheet is varied by passing the asphalt coated sheet through compression rollers configured to compress the asphalt-coated sheet and form a formed sheet such that the prime portion of the formed sheet has a first thickness and the headlap portion has a second thickness, different from the first thickness. The formed sheet is passed under a film applicator configured to supply a film to the headlap portion thereby forming a filmed sheet. Granules are applied to the filmed sheet to form a granule-covered sheet such that granules do not adhere to the headlap portion. The granule-covered sheet is cut into shingles.