Hi there, we have a three story 1960s house in south London, flat roof about 10x4 m, non-opening single glazed roof light, you know the story. The 2 issues are: 1) the house (top floor especially) is unbearably hot in summer. The roof is concrete without any felt, but it's stable and has never leaked in the time we've been there. 2) Roof has no eco credentials and is ugly as hell. 3) There is no access to the roof for maintenance, etc. A couple of houses on the row have an accessible roof hatch.

The first priority is to improve the thermal properties of the roof. Am I correct that greening the roof with sedum/wildflowers would help with this (as well as getting a roof light that can open, etc)? As I understand it, the process requires several new layers of insulation and waterproofing on top of the existing roof surface which would help reduce heat absorption. The plants then do their bit to deflect/absorb heat.

The second priority is to bring the roof into the 21st century. So, greening achieves this but how about some mutually complementary mounted PV panels. Supplier tells me that I would need 6 at a minimum. Trouble is this doesn't leave a huge amount of space for the greening, so am wondering what the balance is. Would PV panels also help us with our temperature issue by deflecting heat off the roof in summer?

And finally, it's of course the south facing rooms of the house that get too hot in summer. Should this be factored into the layout of the roof, ie. what should be the roof surface (PV panels or greening) over south facing part?

Couple of examples attached if anyone is interested. Be really grateful for your thoughts.

insulating it will make the biggest difference,
Green roofs look nice but can be counter productive if your lugging lots of materials up there to keep them alive ( earth, rooting mediums etc).
Personally Id insulate it to current standard ( U=0.1, >150mm polyurethane insulation ) and stick as much Pv up there as you can fit , forget the green roof.
generating energy will do more for the 'environment' than a green roof.
economies of scale means a larger PV system will give you more benefit per negative (if that makes sense)

If you insulate the roof well (which should be your top priority) then deflecting heat off the surface with PV panels won't make a significant difference to internal temperature.

Greening the roof with sedum/wild flowers won't do much for insulation, but is beneficial for wildlife and - if adopted city-wide, would contribute to reducing city temperatures, help cut air pollution, and reduce flood risk. However you'd need to check that the roof can support the additional load.

PV panels are also good environmentally, and - subject to planning permission - could be used to create an overhang on the south side to shade windows from the midday sun.

Combining a green roof with PV is also useful, particularly if you are able (and permitted by planning) to raise the panels to grow the sedum beneath them. The shading of the panels adds another variation to the habitat, and moisture from the green roof reduces the air temperature around the PV panels, making them more efficient.

Can you guys please shed some light on how I begin this process since it requires input from both PV and green roof perspective? Who, effectively, creates the design for this project that I can put in front of planning and get permission for?