 |  |
| Laitance | An accumulation of fine, powdery aggregate particles on fresh cement caused by the upward movement of water; indicates that too much water was used in the mix resulting in poor surface adhesion for a waterproofing layer. |
| Laminated Shingles | See Dimensional Shingles or Architectural Shingles. |
| Lap | The part of the roofing material that overlaps a section of adjacent material. |
| Lap Cement | Asphalt-based roof cement used to adhere overlapping plies of asphalt roll roofing. |
| Lap Seam | Where two material that overlap are sealed together. |
| Lead | Metal used for flashing material. |
| Leader Head | A component used to direct water from a through-wall scupper to a downspout. Also known as a Collector Head. |
| Leader Pipe | A conduit for carrying water from a gutter, scupper, drop outlet or other drainage unit from roof to ground level. Also known as Downspout. |
| Lift | The rise in Sprayed Polyurethane Foam resulting from a pass. |
| Live Loads | Temporary items on a roof such as equipment, people, snow, etc. which the roof must be designed to support. |
| Loose-Laid Roof Membranes | Roofing material attached only at the perimeter and at penetrations and held in place by ballast, pavers, or other materials. |