'L'
| Lean-to Roof | - | Sloping roof supported along its highest part by a taller adjoining wall |
| Light | - | Subdivision of a window - fixed or opening. Opening light can be top or side hung |
| Lintel | - | Concrete or steel beam over opening to support wall above |
| Loose-Fill Insulation | - | loose material for insulating cavity walls and lofts |