Outbuildings are attractive solar sites because they are often unshaded and easy to reach, and they are the structures least likely to have been designed for extra load. A garage roof, a conservatory roof and a flat's roof each raise a different question: can it carry it, can it be fixed to, and are you allowed to.
Garage roof solar panels are usually fine and should still be checked
A modern attached garage with a tiled pitched roof on standard trusses normally takes an array without difficulty. The cases that need a look are lightweight prefabricated garages, older concrete sectional buildings, asbestos cement roofs and anything with a long unsupported span. The other question is the cable route: a detached garage means a buried or clipped run back to the house consumer unit, and a submain rather than a flex, which is real electrical work and should be priced.
Solar panels on conservatory roof glazing are usually the wrong answer
A glazed or polycarbonate conservatory roof is not a mounting surface: the glazing bars are not designed for point loads, the panels would shade the room they sit on, and the weathering detail has nowhere sensible to go. Where a conservatory has a solid tiled replacement roof, built as a structure with rafters, it becomes a normal roof question and the answer changes. The honest response to panels on a glass conservatory roof is that the main roof or a ground frame is where they should go.
Solar panels for flats UK leaseholders: the consent question comes first
In a flat the roof is almost always common parts owned by the freeholder rather than by you, so the technical question is secondary to the legal one. You need the freeholder's consent, usually a licence for alterations, and probably the agreement of the management company; the lease will say who owns the roof and who is responsible for it. Then there is the metering question, because generation has to connect to your own consumer unit rather than to the landlord's supply.
When an outbuilding is genuinely the best site
A south facing garage or workshop roof that is unshaded, easy to scaffold and structurally sound can beat a shaded house roof comfortably. The comparison to make is modelled generation rather than convenience: a clear outbuilding roof with a longer cable run frequently produces more per pound than a compromised main roof, and the extra electrical work is a one off cost against twenty five years of output.
Questions people ask about solar panels on garage roof
Can a garage roof take solar panels?
Usually yes if it is a conventional pitched roof in good condition on standard trusses. Lightweight prefabricated, sectional concrete and asbestos cement roofs need checking, and a detached garage adds a cable run back to the house.
Can you put solar panels on a conservatory roof?
On a glazed or polycarbonate roof, no in practice: the structure is not designed for it, the panels shade the room and the weathering detail is unresolvable. On a solid replacement conservatory roof it becomes an ordinary roof question.
Can solar panels for apartments go on a shared roof?
Only with the freeholder's consent, because the roof is normally common parts. Check the lease first, then expect a licence for alterations, and settle how the array connects to your own supply rather than a communal one.
Is an outbuilding roof worse than the house roof?
Not necessarily. An unshaded outbuilding roof often outperforms a shaded house roof by enough to pay for the longer cable run several times over. Compare modelled generation, not distance.