Above-rafter insulation desired with existing photovoltaic system

Hello everyone,

I have been reading along for years, recently created my own profile. Here is my first real question.

First of all: Does anyone know how to display more than 5 posts per page? Clicking through long threads is tedious.

Now to the actual question. It is quite interdisciplinary (roof, insulation, photovoltaic), which is why I hope I have chosen the right subforum. There isn't a pure roof subforum after all... We are considering buying a house built at the end of the 70s. The roof is covered with concrete roof tiles, the south roof surface is almost completely covered with a photovoltaic system. The attic is hardly insulated. In the 80s, an attempt was made with cavity insulation between rafters as a DIY job, but it was abandoned halfway through. It still partly hangs there tattered. The attic is expandable, but this also did not happen due to declining motivation of the builders.

The building savings contract now recommends external roof insulation to ensure sufficient summer heat protection (bedrooms planned). After extensive research, I have found some information on photovoltaic systems with external roof insulation, but always only in the sense that the external roof insulation was already there and then a photovoltaic system was to be installed – with discussions then focusing on the more complex fastening to the roof's supporting structure. But how do you proceed in the opposite case?: Photovoltaic system already there, then installing external roof insulation "underneath"? Does anyone have experience with this? The photovoltaic system is already over 10 years old, which is why it will probably be difficult to obtain the right mounting material, if it has to fit exactly to the installed type. Or is it standardized enough that I don't have to worry about that?

And then I have one more question about it: On the internet, you find very different information regarding the lifespan of concrete roof tiles. Everything between 30 and 80 years is mentioned. But would one generally always reroof with external roof insulation – especially with roof tiles that are about 40 years old?

Thanks and greetings from
Pröter

what about a cellulose blown-in insulation as under-rafter insulation?

Taking photovoltaic panels down and putting them back on is not a special act; fastenings are usually universal. I would not choose worse insulation just for 2-3 days of screwing work.

First of all: Does anyone know how to display more than 5 posts per page? With long threads, clicking through gets tedious.

No, unfortunately not. But with the absurdly many ads, I'm already grateful that you don't have to click after every post at all....

what about cellulose blown insulation as below-rafter insulation?

According to the assessment by the building savings contract, this is not sufficient to achieve an adequate insulation value.
And if the roof needs to be re-covered anyway (the question about the lifespan of the concrete roof tiles is still open), then as far as I know, the above-rafter insulation is far superior.

Taking down and putting back photovoltaic panels is not a special act; fastenings are generally universal

I had imagined that to be more difficult. Thanks for the assessment!

I think like that this will be feasible. You certainly don't have to replace the roof tiles, but after 40 years I would also replace them out of feeling, especially since removing, carefully storing, and reinstalling is probably more effort than completely reroofing. Additionally, some tiles might be damaged and you may no longer have enough of them. Ultimately, the roofer has to tell you that. With new ones, you could also renew the battens and underlay. Inside, you probably don't have planed rafters for an exposed roof structure, right? How do you want to do that?

to achieve a sufficient insulation value

What value do you want to achieve? It also depends on which insulation and thickness you want to apply; that again brings things along because the roof will become "thicker." With us, the energy consultant calculated 24cm PUR! That's a block o_O