Building Design and Construction Handbook - Merritt - Ventech!

12.10 SECTION TWELVE
mechanical spreaders, styrene-ethylene-butylene-styrene (SEBS) polymers are utilized.
12.4.5 Single-Ply Roof Coverings
The single-ply family of roofing materials includes some distinctly different products.
(Modified bitumen products [Art. 12.4.4] are sometimes included in the singleply
category.) The single-plies can be classified as either thermoset or thermoplastic
materials. Thermoset materials normally cross-link (cure) during manufacturing.
Once cured, these materials can only be bonded to themselves; for example, at a
seam. Bonding is accomplished with an adhesive. Thermoplastic materials do not
cross-link. Therefore, they should be capable of being welded together throughout
their service life. Welding is usually accomplished with hot air.
There are three primary methods for attachment of single-ply membranes to a
roof deck. In the ballasted system, the membrane is laid loose over the substrate
and then covered with ballast to resist uplift from the wind (Fig. 12.5a). The ballast
can either be large aggregate or concrete pavers. In the second method of attachment,
the membrane is fully adhered in a continuous layer of adhesive (12.5b). In
the third method, the membrane is mechanically attached to the deck (Fig. 12.5c).
The mechanically attached system generally utilizes screws with stress plates,
or metal batten bars, located within the membrane lap (seam). Alternately, the
battens may be placed on top of the membrane and covered with a stripping ply
of the membrane material. There are other variations of the mechanically attached
system, many of which are proprietary to a single membrane manufacturer.
Following are descriptions of single-ply membrane materials.
(a)
FIGURE 12.5 Methods of installing single-ply membrane over
insulation board: (a) ballasted; (b) fully adhered; and (c) mechanically
attached.