4.1 General

4.1.1 The primary function of a roof deck is to provide structural support and restraint for the roofing system. The deck must have adequate strength and rigidity to support all anticipated live and dead loads, foot or construction traffic, wind, rain and snow loads. The deck must have adequate strength and rigidity to carry the weight of the roofers and their equipment during construction, without deflecting to the point where roofing components rupture, delaminate, or are weakened.

4.1.2 Some decks are designed to furnish inside appearance as well as sound control, however, JM’s concern is for the roof deck as a base for the roofing system. To perform this function, the deck must be rigid. It must be smooth and free of large cracks, holes or sharp changes in elevation of the surface. It must be able to receive the roof system by some method which will hold the system securely, either by adhesion, ballast or mechanical fasteners. Before roofing work is started, the deck should be  inspected carefully by the roofing contractor, the deck contractor, and the owner’s representative, to determine that it satisfies these conditions. The roofing contractor and JM are only concerned that the surface of the deck will accept the roofing system. Neither JM nor the roofing contractor have any responsibility regarding the adequacy of the deck from a structural standpoint.

4.1.3 Surface preparation should include filling and smoothing all holes, depressions, irregularities, etc. before the roof is applied.

4.1.4 Providing a deck for the roof system that meets these criteria is the responsibility of the designer of the building, for only he is in a position to integrate these requirements with other structural and use considerations. JM can only assume that the deck is manufactured  and installed in accordance with the manufacturer’s current specifications.

4.1.5 Roof-mounted equipment should not rest on the deck or roofing system. It should be supported by the structural framing of the building. Leaks resulting from improperly mounted roof- top equipment are excluded from coverage under the JM Roofing System Guarantee.

4.1.6 To be a satisfactory substrate for any roofing system, a roof deck must have:

A. Proper construction, following the deck manufacturer’s instructions.

B. Proper design to carry maximum anticipated live and dead loads which may be encountered during and after construction, without excessive deflection.

C. Positive drainage which will not allow water to pond. (See Paragraph 4.3 of this section on Roof Drainage.)

D. Expansion joints to allow for movement of the structure without causing strain on the roofing membrane. To be effective, expansion joints must extend through all elements of the roof and structural system.

E. A smooth, dry and properly cured surface to which the roofing system can be installed.

F. A solid, rigid assembly when using pre-cast deck units. Units must be securely fastened to supporting members to prevent movement.

G. A continuous, uninterrupted surface. Installation of conduits on the top surface of a roof deck is not acceptable, unless the area between the conduits is filled with an acceptable roof insulation, properly secured, and a full thickness of roof insulation installed over the conduits.

H. A clean surface. Before roofing application is started, the deck should be free of all dust, dirt, debris and foreign material. Only the roofer’s tools and equipment should be allowed on the deck during roof application.

I. The proper resistance to wind uplift to prevent rupture of the roof membrane.

J. Adequate means of membrane securement. Provisions for special attachment procedures must be made on steep-slope decks. (See Paragraphs 6.11 and 7A.29 of the current JM Commercial/Industrial Roofing Systems Manual for details on nailing strips.)

K. Appropriate termination details. Under certain conditions, consideration should be given to isolating the roof membrane from stresses caused by deck or structural movement. This can be accomplished by securing base flashing to curbs attached to the structural deck and not allowing membrane base flashings to be secured directly to vertical walls. (See Section 8 for details.)

4.1.7 Any decks or substrates not listed in the current JM Commercial/Industrial Roofing Systems Manual must be approved by a JM Technical Service Specialist in writing prior to the installation of a roof which is to receive a JM Guarantee. Such approval only indicates that JM accepts the deck surface to receive a JM roofing system. By such acceptance, JM accepts no responsibility of the structural adequacy or performance of the deck.

4.1.8 Except in Region 3, if a JM Roofing System Guarantee is required, the use of under-deck insulation must be approved in writing by a JM Technical Service Specialist prior to installation of the roofing system.

4.2 Wood Nailers

4.2.1 Wood nailers or curbs should be installed around the perimeterand openings in the roof deck for securement of roofing membranes, edging, gravel stops, and roof fixtures. Nailers should be installed to provide a minimum of 200 lbs. (890 N) uplift resistance, at any point. Nailers should be installed so that the top of the wood nailer is flush with the membrane substrate (which is typically a rigid roof insulation material). Wood nailing strips are also required for back nailing of built-up roofing and modified bitumen roofing felts to prevent sliding or slippage over non-nailable decks when roof inclines exceed published limitations.