Various choices are available for all roof types. Usually the type of material used is based upon factors such as cost, climate, and type of roof design.  Roofers often make recommendations based upon service experience and supplier support.  Some are more sustainable than others.

Metal panels are used for both low and steep sloped roofs. They are the roof of choice for aesthetics and sustainability. They are most easily maintained and generally require the least maintenance. They also come with an initial higher price tag. They are referred to as either structural (the roof supports itself) or non-structural (requires deck support).

Low sloped roofs are usually structural roofs; the panels are designed to overlap and be connected together and provide a rigid surface that support loads and also sweep water away. They usually are built atop perlins (evenly spaced open supports) beneath and should be of a heavy enough gauge that foot traffic or dead loads do not damage seams or panels. Do diligence when pricing a new structural metal roof to compare steel gauges. Unscrupulous roofers lure purchasers using lowball replacement pricing based upon thin metal or siding for roofing. The flaw of this thinking comes back to haunt buyers too soon to make this a practical decision. These can become chronic problems once seams open up, because even the weight of workers attempting maintenance can open more seams and cause more grief.

Steep slope roofs can be non-structural, meaning that a full deck is below and the panels do not support loads. Non-structural roofs also are referred to as Architectural roofs, largely because they are designed primarily for aesthetics. The skin essentially sheds the moisture but it is the slope and decking below which largely influences waterproofing. They are held together by a series of hidden metal clips fasteners.

Lap types vary, including side seams, exposed fasteners, elevated standing seams, hidden metal clip fasteners or a hybrid. Exposed fasteners require periodic tightening. After a period of time, fasteners can come loose from the years of thermal induced movement. After components are inspected, and damaged or missing ones replaced, these roofs are easily maintained with an approach that provides thorough attention to fasteners, seams, and a protective finish coat to extend weathering. This is where choosing a coating correctly, is meaningful.

Built-up (multi-ply) and Modified Bitumen are some of the most common membranes for flat roofs (“flat” should not be less than ¼”/ft. slope per NRCA guidelines). Though initial costs are higher than other options, traditional installation techniques, durability, and longer term maintainability lend to their popularity and economy. These involve multiple plies which provide greater environmental protection. They may be granular covered to enhance protection against UV and hail. Most all are insulated, so care should be taken to remove any damp insulation and rebuild the affected area when doing any maintenance. They accept maintenance coatings well. These 99% of the time are “hot applied” – temperature of the bitumen is important during installation to get proper bonding. The disadvantage is the danger of burns (hot kettles with mop-on installation) and fire from torch-on modified bitumen. VOC laws and insurance issues are making their installation more difficult in some areas. If attended to properly they are renewable without full tear-off.

SEBS Modified Cap Sheets to their credit contain SEBS rubber, which is the most sable thermoplastic known. They are some of the most expensive of Modified caps sheets and they are among the more durable. SEBS is excellent in all climates, hot and cold. Often however the rubber is blended; more typical is (80%) SBS (see below) with just 7% SEBS and this rubber blend typically makes up <7% of the membrane. The balance (93%+) consists of bitumen and fillers. They are usually applied into hot asphalt subject to the above considerations (see Built-up and Modified Bitumen). These cap sheets always have either a granular surface or are flood coated. They require application of a highly reflective maintenance coating to achieve energy savings. If attended to properly they are renewable without full tear-off.

SBS Modified Cap Sheets contains SBS rubber which is a thermoplastic with good weatherability. They are excellent in all climates hot and cold. However, unlike SEBS rubber, SBS rubber undergoes crosslinking, which makes it brittle as it ages. They are usually applied into hot asphalt subject to the above considerations (see Built-up and Modified Bitumen). These cap sheets always have either a granular surface or are flood coated. They require application of a highly reflective maintenance coating to achieve energy savings. If attended to properly they are renewable without full tear-off.

APP Modified Cap Sheets (Atactic PolyPropylene) is not actually a rubber but is more of a plastic polymer and is less costly. It installs easily and is easily maintenance coated.