Commercial and institutional buildings typically have steel or concrete roof decks, although plywood or OSB decks are also used on smaller buildings. The deck can have significant influence on the roof system.
Of the deck types used today, steel is the most common. Although prime-painted steel decks with welded connections are commonly specified, it is recommended that galvanized decks be specified in order to obtain greater corrosion protection in the event of roof leakage. It is also recommended that screw, pneumatic, or powder actuated-attachment be specified in lieu of welding, because screws provide more reliable attachment. Refer to the NRCA’s Industry Issue Update, “Moisture in Lightweight Structural Concrete Roof Decks.”
Also, the NRCA recommends steel roof deck installations conform to the requirements described in the Steel Deck Institute’s (SDI’s) Manual of Construction with Steel Deck and Composite Steel Deck Handbook. Review attachment with structural engineer who makes the final decision and specifies. In cold climates, it is a common occurrence for interior vapor to pass through simple laps in steel decking, and then condense in the roofing insulation to saturate the insulation and leak back through the deck joints as free water. In the case of cold climates, it is always best to provide a continuously sealed vapor barrier under the roof insulation, on top of the steel decking. If roofing materials are to be adhered to a new concrete deck verify that the concrete is cured, sufficiently dry, and that moisture test results are within the manufacture’s recommendations for good adhesion.
Make sure the structural engineer designed the deck for the wind uplift loads, especially at the perimeter and corner zones.