Single-Ply membranes are not like BUR systems or modified bitumen membranes. Single-Ply membranes have just one layer. The membranes might be thick as 120 mils. Mil is a common term in roofing. There are 1,000 mils in an inch.

Single-Ply Installation Methods

There are three ways to install single-ply membranes. One method is loose-laid and ballassted. Another method is mechanically attached. The last method is called fully adhered.

Loose-Laid and Ballassed Method

The membrane is laid out loosely and only attached in a few places. It is attched at the perimiter(the edges) and the places where there are flashings. After the membrane is laid down, ballast is put on top of it. Ballast is usually aggregate or concrete pavers, which are concrete slabs.

Some loose-laid and ballasted systems are protected membrane roofs (PMRs). This means that they are installed in the reverse order from common roof systems. This sys-tem protects the membrane. Some BUR systems are PMR systems, as well. PMRs are also called upside-down or inverted assemblies.

The membrane is laid out on the deck. Roof board insulation is laid on top of it. Then, ballast is laid down. A protective mat is placed on top of the insulation if aggregate is used.

Mechanically Attached Method

Mechanically attached systems are attached to decks with fasteners.

Fully Adhered Method
Fully adhered systems are bonded. Adhesive is used on the entire field to adhere a roof membrane to a substrate. A substrate is the component under a membrane.