The short answer
If the covering is close to worn out, fit the panels as part of the re-roof, or at least renew the covering first. Panels last a long time, and taking them off later to re-roof costs more than doing the roof once. Sharing the scaffold also saves money. The choice is on-roof panels, fixed above the tiles, or in-roof panels that replace them.
Why timing matters when you want solar panels and a new roof, how on-roof and in-roof systems differ, and what to check first.
Why timing matters
Panels stay up for many years, so the covering beneath them should outlast them or be renewed with them. If you fit panels on a tired roof and the tiles fail later, the panels have to come off before the roofer can work, and then be fitted back. That is a second scaffold, a second visit from the installer and a gap in the panels' output. Doing the roof first, or together, avoids all of it.
The covering gives a rough guide. Marley gives concrete tiles around 60 years, without promising it. The Building Research Establishment gives clay a minimum life of 60 years, though old peg tiles do not fit that figure well. If your roof covering is well into its life, a survey will show whether it has enough left to carry the panels or whether it should be renewed first.
If the roof is sound, there is no need to re-roof for the sake of it. A survey, with photos of the battens, membrane and fixings, shows what condition they are in. Our answer on whether a new roof adds value looks at the other side of the choice, and the roof replacement page explains the job.
In-roof or on-roof panels
On-roof panels are the common choice. Brackets are fixed through the covering to the rafters, with rails across them, and the panels sit above the tiles with a gap beneath. Each bracket is a hole in the roof covering, which has to be sealed or flashed, so the quality of the fitting at the tile matters. A re-roof is the perfect moment to have the brackets fixed to new battens and rafters that have just been checked, and to have the roofer and the installer agree where every fixing goes.
In-roof panels replace the tiles in the area they cover, and sit flush with the surrounding roof. They are watertight surfaces in their own right, with flashings round the edge. They look neater and suit a new roof, but the roofer and the solar installer have to work together, because the waterproofing of the roof depends on both, and a fault in the join between panel and tile can leak.
Either way, the questions are the same. Who is responsible for the roof's watertightness around the panels? Who can repair a tile near them? Get both answers in writing, and ask the installer for the maker's fixing details for your covering.
Weight, scaffold and who does what
Panels add load, so the rafters need checking. If a re-roof alters the load on the structure, Planning Portal suggests having a surveyor or structural engineer assess it before work begins, and it says a covering adding 15 per cent or more to the old weight needs approval. That test is about the covering, but the same caution should apply to anything heavy you add to it. Ask the installer what their system weighs per square metre and who has checked that your roof can carry it.
The scaffold is where the savings are. Checkatrade's October 2026 roof replacement guide cites £700 to £1,300 for scaffolding a new roof, as a national yardstick. One scaffold shared by the roofer and the installer, with a programme that has them in sequence, costs less than two separate hires. A scaffold on the public pavement needs the highway authority's licence, which we line up with the scaffolder; in West Sussex, allow at least 10 working days from application.
Agree the order of work before the scaffold goes up. The roofer finishes the covering, the installer fits brackets and panels, and the roofer returns to check the flashings.
Planning, VAT and what to ask
Solar panels have their own permitted development rules, separate from the class that covers roof alterations, and extra limits apply to a listed house or a home in a conservation area. Class C even names the installation, alteration or replacement of solar photovoltaics as outside its own scope. Check with the council's planning team for your address, which in Crawley is Crawley Borough Council.
On VAT, GOV.UK says the zero rate on energy-saving materials runs to 31 March 2027, with the reduced rate of 5% applying after that. Whether your own job qualifies turns on the equipment and who fits it, so get the installer to confirm the rate in writing. The standard rate is 20%, so look at whether each quote includes VAT and the scaffold.
Government schemes are changing. ECO4 is due to run until 31 December 2026, Great British Insulation, the scheme that paid for loft and wall work, stopped taking installs after 31 March 2026, and no national scheme funds re-roofing. Check gov.uk for the current position before relying on any grant.
A picture of the slope you have in mind and the age of the covering are a good start. We survey, send you photos of what is there, and put one total in writing. The panel supplier works to their own quote, so keep the two clear.
More on this in Roof Replacement & New Roofs in Crawley
Two solar roof questions
Can existing panels stay up during a re-roof?
Not usually. The covering beneath them has to come off, so the panels are taken down by the installer, stored and refitted after the new roof is on. Book that into the programme, agree who pays for it, and ask the installer to retest the system. It is another reason to plan the roof and panels together.
Will new panels shade or damage the tiles beneath them?
Fixings through the covering are the main risk, as each one is a hole to be sealed. Leaves and moss can also collect behind the panels, so leave room for a roofer to reach under them. Ask for a plan for maintenance and cleaning before you buy, particularly if you have overhanging trees.