 |
ROOF DECKS |
4.3.7 Standing water can increase the load
on structural decks. If the water stands for long periods, algae or other vegetation may
form. A continuously wet or moist environment can also attract undesirable insects or
vermin. This can damage the roof membrane and create a possible hazard to health.
Vegetation and debris will clog drains so that even more water ponds, which in winter can
freeze and block water from entering the drain. As more water accumulates, the deck may
deflect, increasing ponding of water. This has been known to cause collapse of the roof
deck.
4.3.8 JM will not be responsible for any
damage caused to the roofing system or the structure and contents due to ponding water. JM
cannot be held responsible for determining if a roof deck will pond water or will drain
properly, either before or after application.
4.3.9 JM recommends that roofing
contractors and designers use the following guidelines to assure adequate drainage of the
roofing system:
| A. |
Provide maximum number and size drains
practical for the roof area, and locate the drains at low areas in the roof system. |
| B. |
Design raised edges and gravel stops by
incorporating tapered edge strips at the perimeters when internal drains are employed. |
| C. |
Install drains in sumps to assure drains are
below the roof level, or taper the deck or roof insulation to eliminate ponded water at
drain locations. |
| D. |
Drain outlets should have proper strainers to
prevent debris from clogging carry-off pipes. Strainers must be maintained to prevent
blocking. |
| E. |
Provide scuppers secured to wood nailers and
flashed into the roofing system when interior drains are not used. |
| F. |
Follow the recommendations of local plumbing
and building codes for number and size of drains and carry off pipes. |
| G. |
Drains should be located in every area of the
roof, preferably not more than 75' (22.9 m) apart, with no leader or carry-off pipe less
than 3" (76 mm) in diameter. It is recommended that two drains minimum be installed
on any roof area as a safety factor; if one should cease to function, the second
drain will be available to prevent excessive build-up of water. Roof areas surrounded by
parapets must have through-wall scuppers to allow for overflow in the event drains become
blocked. |
4.3.10 JM manufactures the JM Flex-I-Drain
which may be used in original installations as well as retrofit projects to provide
adequate drainage. Details are included in Section 8 of the current JM
Commercial/Industrial Roofing Systems Manual. Flex-I-Drains can be included in a JM
Roofing Systems Guarantee when installed according to published specifications.
4.3.11 JM offers RetroDrains designed
specifically for use when reroofing an existing roof system with existing roof drains.
They are installed in the new system with sleeves designed to tie into the existing
drains. For information, see Section 10 of the current JM Commerical/Industrial Roofing
Systems Manual.
4.4 Expansion Joints
4.4.1 Every designer of a
building must consider the reasonably anticipated movement of the structure in his design,
and compensate for it by placing construction and expansion joints in the structure. The
decision as to the use and location of expansion joints is the professional responsibility
of the designer and structural engineer. Only the design professionals are familiar with
all the factors involved in
structural design.
4.4.2 JM offers the following suggestions
where expansion joints may be employed:
| A. |
Whenever roof deck materials
change or deck materials of a similar type change in direction (i.e., steel deck changing direction or interfacing with a dissimilar
deck material). |
| B. |
Whenever roof structures change in direction,
such as, "T", "H", "L", and "U" shaped buildings. |
| C. |
At each building expansion joint or expansion
joint in roof deck material, the roof should have a corresponding
expansion joint. |
| D. |
If the length or width of a section of
unbroken roof area exceeds 200' (61 m)
an expansion joint or roof divider should be installed near the center of each direction,
at points not over 200' (61 m) apart. |
| E. |
Whenever an addition is made to an existing
structure. |
| F. |
When seismic movement is anticipated. |
4.4.3 Expand-O-Flash expansion joint
covers can be included in the Roofing
System Guarantee if installed in accordance with JM instructions.
4.5 Steel Decks
4.5.1 Today, steel decks are the most
common substrate for commercial/
industrial roofing systems and can provide an excellent base for built-up, modified
bitumen and single ply roofing systems, when properly specified and installed.
4.5.2 Factory Mutual Research
Corporation’s Loss Prevention Data
Sheet 1-28, 1-29 and the Factory Mutual Research Corporation Approval
Guide contain comprehensive and specific information concerning the design and use of this
deck system and roofing systems used above this deck. To be eligible for a JM Roofing
System Guarantee, all requirements contained in these three documents must be met.
4.5.3 In conjunction with, or in addition
to, the Factory Mutual
Research
Corporation 1-28 and 1-29 requirements, the following guidelines must also be followed to
qualify for a JM Roofing System
Guarantee:
| A. |
Steel deck must be
minimum 22 gauge (0.76 mm) and, at a minimum, have a shop coat of priming paint.
Galvanized steel deck is recommended. |
| B. |
Steel deck units should be welded or,
preferably, mechanically fastened to
the structural frame, with a minimum of weld holes. Side laps should be fastened with
sheet metal screws on not over 3'-0" (0.91 m)
centers. |
| C. |
Individual deck units should be flat and
without large dents, buckles, or holes. Individual deck pieces should not be more than 1/4
" (6 mm) out of plane with one another. |
| D. |
Deck openings exceeding 12" x 12"
(305 mm x 305 mm) should be reinforced, and wood nailers of the same thickness as the
proposed insulation installed, or prefabricated curbs installed, which provide nailing
facilities for flashing. |
| E. |
A salt preservative-treated wood nailer must
be installed at all roof edges, gables, or curbs, equal in thickness to the proposed
insulation and tapered edge strip. |
