Headlap | Article about headlap by The Free Dictionary
In the lapping of roofing shingles, the shortest distance between (a) the lower edge of an overlapping shingle and (b) the upper edge of the lapped unit in the second course below.
References in periodicals archive
Elk Prestique Grande hybrid shingles with the signature High Definition(R) look are made with a patented new VersaShield(R) XP(TM) headlap
Elk's Prestique(R) Grande shingle, featuring its patented VersaShield(R) XP headlap
technology, has gained market acceptance in fiscal 2005.