Some of the best solar projects start with a problem on the roof. At Booker's Watford cash-and-carry, the existing roof was due for replacement, and the business also wanted to cut operating costs, improve energy efficiency and secure long-term structural reliability. Rather than treat those as separate projects, the roof replacement became the moment to integrate solar. You can read the headline facts in the Booker Watford case study; this spotlight looks at how the pieces fitted together.
The client's problem
A large warehouse roof that is nearing the end of its life is a poor place to mount a solar array. Panels are designed to generate for decades, so fixing them to a roof that will need replacing within a few years means paying to take the array down and put it back up again. We explain the reasoning in more detail in our guide on why you should re-roof before adding solar.
Booker's priorities were clear: lower energy bills, better efficiency and a building envelope it could rely on. The challenge was to deliver all three without running two disconnected programmes on the same roof.
On site
How the work was approached
The project was delivered through a partnership between Cornerstone, which handled the solar, and NWIR, which handled the roofing. Planning the two together meant the new roof and the array went on as one job, rather than one contractor finishing and another arriving later to start again.
The roof itself was specified as a high-quality, weather-resistant roof engineered to carry the panels. That matters: the roof is not just a surface for the array but the structure it depends on for its whole working life. Our roof cladding team works with twin-skin, composite and single-skin systems, and choosing the right one for the building is the first step in any combined scheme.
Designing the array around the site
On top of the new roof sits a 334 kWp array using smart inverters. Two design decisions shaped how it performs:
- Export capped at 200 kW to meet DNO requirements, so the system could connect without breaching the limits set for the local network.
- On-site consumption prioritised, so as much of the generated power as possible is used by the building itself rather than bought from the grid.
Prioritising self-consumption is usually where the strongest savings come from, because every unit generated and used on site displaces a unit that would otherwise be bought at full grid price. DNO applications, export limiting and performance monitoring are all part of our commercial solar panel service.
What was delivered
Booker received a new roof with integrated PV and a 334 kWp rooftop system. Both the roof and the solar system carry a 20-year warranty, giving the business cover across the two elements that matter most to the long-term success of the installation.
The outcome
The figures speak for themselves:
- A 3.1-year payback period
- Materially lower energy bills
- Additional revenue from exported power
- Low ongoing maintenance
- Roughly 70 tonnes of CO₂ saved a year, supporting Booker's sustainability goals
A 3.1-year payback sits comfortably within the range we typically see on commercial systems. If you want to understand what drives that number, our explainer on commercial solar payback walks through the main factors.
"The combined expertise of Cornerstone and NWIR delivered a seamless roof and solar solution, with immediate savings and long-term reliability." Booker Watford, Facilities Manager
What it shows about roof and solar together
Booker Watford is a clear example of why the roof and the array should be planned as a single programme. Two contractors working separately can mean two warranties, a grey area where the roof meets the panels and the cost of mobilising twice. Coordinating the work removes most of that friction.
We have since taken that idea further. Today, when Cornerstone fits the roof and installs the solar, both are covered by a single combined 30-year roof and solar warranty, with one point of contact for the life of the roof and the array. Booker Watford's 20-year warranty reflects the arrangement in place at the time of that project.
The same thinking runs through other work in our roofing and cladding division. At Lovania Nurseries, a fragile cement-fibre roof had to be replaced before a 50 kW array could go on, and at Booker Newton Abbott a 114 kW system was added to another Booker site.
Planning something similar?
If your roof is due for attention and you are weighing up solar, we can look at both together and model your savings and payback before you commit. Tell us about your project or call 0800 011 9758.
Power your business with solar.
Our renewables team designs, installs and maintains commercial solar, storage and EV charging across the North West and the UK.