Flat roofs are prone to leaking even without decks because of design errors, improper materials, and improper installation. Many times when roof decks are installed they further damage roofs causing more severe leaking and drainage problems. Proper waterproofing for a roof deck involves installing an EPDM membrane and flashing around deck supports and rail penetrations. This is often accomplished using EPDM boots that fit over the openings. EPDM is a rubber like sheet used for waterproofing surfaces. Roofs should be sloped about 1/4" every 12" to shed water. Drainage is very important because pooling water can cause leaks.