As long as there is enough space and enough access to the sun, solar panels can be installed on just about any roof. The way the panels are attached to the roof depends on the type of roof. And, therefore, the cost to install the panels will vary as well. Solar panels will actually reduce some of the weather-related wear on the parts of roof they cover. But they are not a substitute for a roof replacement (unless one is using solar shingles). So if a roof has existing problems or is approaching the end of its warranty, it should be replaced before installing solar panels.
When installing solar panels, it is important to consider both the angle of the roof that the panels will be installed on and the direction that the roof faces. To capture adequate amounts of sunlight, panels should face south to the greatest extent possible and should be mounted at an angle as close to the latitude of the site as possible. These two requirements generally do not prevent buildings from installing solar panels; however, they do determine what kinds of installations are possible on specific roofs and determine the performance of the resultant installation.
Common roof types on homes include gable roofs, cross-gabled roofs, hipped roofs, and cross hipped roofs. All of these have moderate pitches and can be ideal for solar installations, provided that they have sufficiently large south-facing surfaces. These roof types are amenable to installations where photovoltaic shingles are desired rather than separate panels.
Flat roofs - which are commonplace on commercial buildings – and even more exotic roofs such as Mansard-style roofs can actually provide a great starting point for highly effective solar installations. On a flat roof, the solar panels are typically installed on free-standing frames that can optimize array performance by providing the ideal tilt and directional orientation. The same is true for Mansard roofs that include relatively large flat spaces. The only obstacles that cannot really be overcome are roofs that don’t have south-facing surfaces (such as some shed-style roofs) and sites with unacceptable amounts of shading from nearby trees or structures.
The cost and complexity of installing panels varies with the design and the composition of the roof. Most roofs use composition shingles and solar panels are attached to rails that are affixed to the roof through bolting mounts into the roof rafters. Flat roofs are typically covered with either tar and gravel or polyurethane foam. The racks that hold the panels generally don’t require drilling into the roof structure at all; often some kind of ballast such as concrete blocks is used to keep the racking stable. Roofs with wooden shake shingles or ceramic tiles are the most expensive roofs to install PV modules on. This is because the shingles are fragile and difficult to walk on and drilling into them for mounting the racking is delicate work and time-consuming.
There are, of course, more exotic roofs around with complex curved surfaces and other unusual features. Such roofs present unique challenges to PV installers but, provided that there is enough space, enough sunshine and enough determination, solar panels can be installed on nearly any roof.