3. Mechanically Attached: The membrane is loose-laid except for a discrete rows of fasteners. There are a variety ways of fastening and fabricating seams with this method, as described in A Guide for the Wind Design of Mechanically Attached Flexible Membrane Roofs which is available from the .

Figure 8. This mechanically attached single-ply membrane uses the “bar-over” attachment method. After installation of the membrane, a batten bar is placed over the membrane and screwed to the deck. A stripping ply is then installed over the bar.

Mechanically attached systems may not be suitable for buildings in high wind zones. Specify an air barrier on the deck (in conjunction with a vapor retarder in cold climates with high humidity interiors or with membranes or on new concrete decks) to prevent wind pumping (see discussions above under air barriers and vapor barriers).

To avoid tear propagation in the event that the membrane is torn, it is recommended that only reinforced membranes be specified for this attachment method.

Because of the mechanical stresses focused on the edges of the sheet and the air pumping which acts to pull interior air into the roof assembly and cause condensation problems, mechanically fastened membranes are not typically considered the best choice.