Tile and slate cover most British roofs and there are good reasons to use something else: weight, pitch, shape, appearance, or wanting the roof to do a second job. Four alternatives come up repeatedly and each suits a particular problem rather than being a general improvement.
Aluminium roof systems and other metals
Aluminium, zinc and steel are laid as standing seam panels or as interlocking shingles and tiles. They are light, which is the decisive advantage where the structure cannot carry tile, they work at low pitches where tiles cannot, and they suit complex shapes such as dormer cheeks and curved roofs. They have long service lives and cost more than concrete tile. The two things to ask about are thermal movement, because metal expands and the fixing system has to allow it, and noise in heavy rain, which is a function of the build up beneath rather than the metal itself.
Fibreglass (fiberglass) roofing, and where it belongs
GRP is a liquid laid laminate cured into one rigid shell, and it belongs on flat and very low pitch roofs, balconies, dormer cheeks and small complex areas where a seam free finish is worth having and the surface may be walked on. It is not a pitched roof covering. Its weakness is rigidity: laid on a deck that moves or was not dry, it cracks, which is why the board specification matters more than the resin.
Green roofs, and what drives the green roof cost per m2
A green roof is a planted layer over a conventional waterproofing system, so it is an addition rather than a covering in its own right: there is still a membrane underneath doing the work. Extensive systems with sedum are shallow and light and need little maintenance; intensive systems are deeper, heavier and are gardens. The deciding constraints are the structural capacity for the saturated weight, the drainage and outlets, and access for maintenance. The benefits are real, including attenuating rainwater and protecting the membrane from temperature swings, and the cost per square metre sits well above a plain membrane.
Integrated solar roofs
An integrated or in roof solar system sits within the roof plane in place of tiles rather than on brackets above them, so the array is the covering over its area. It looks considerably better and it makes the waterproofing and the electrical installation one job rather than two trades, which cuts both ways: get it right and it is neat, get it wrong and a leak is under an array. It costs more than an on roof system and it makes most sense when the roof is being replaced anyway or on a new build, because retrofitting it means stripping the covering.
Solar roof tiles and solar panel roof tiles: the in-roof alternative
Instead of mounting panels above the covering, these replace part of it: the generating units are the weather surface, laid in with the tiles or slates around them. The argument for them is appearance, and it is a real argument on a designated building or a prominent front elevation where a conventional array would be refused or would look wrong. The arguments against are cost per unit of output, which is higher, a smaller field of suppliers, and the fact that a fault or a leak is a roofing job rather than an electrical one. Ask what happens at year fifteen if a unit fails and the product is no longer made.
Questions people ask about aluminium roofing
Are aluminium roofs and other metal roofs noisy in rain?
Much less than people expect on a house, because the insulation and deck beneath absorb most of it. The bare agricultural sheet people remember has no build up under it.
Can any roof take a green roof?
No. The structure has to carry the saturated weight, and the drainage and access have to be designed for it. It is assessed structurally before anything else.
Is an integrated solar roof better than panels on brackets?
It looks better and combines the covering and the array into one job. It costs more and makes most sense when the roof is being replaced anyway, since retrofitting means stripping the covering.