The unionized roofing and waterproofing industry offers employment in the commercial, industrial and residential fields. Roofers must possess the specialized skills needed to install a diverse array of roofing systems, including hot built-up roofing, single-ply roofing, torch-on and mopped modified bitumen, composition shingles, slate and tile roofing, wood shakes and shingles. Water proffers install a verity of systems designed to prevent moisture intrusion into below grade and above grade structures such as foundations, basements, promenade decks and plazas, fountains, reservoirs, tanks and similar structures. Roofers and Waterproofers sometimes work in temperature extremes that demand physical fitness. Roofing work is very labor intensive and requires that those employed in the industry be physically capable of performing the work. Roofers may work at great heights and danged from falling off of reefs or through roof openings is always present, so learning safe work practices through apprenticeship training is a must.