ᐅ Continuous insulation above rafters desired with existing photovoltaic system

Hello everyone,

I have been reading along for years and 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 quite tedious.

Now to the actual question. It is quite interdisciplinary (roof, insulation, photovoltaic), so I hope I have chosen the right subforum. There isn’t a dedicated roof subforum...

We are considering buying a house built in the late 1970s. The roof is covered with concrete roof tiles, and the south-facing roof surface is almost completely covered with a photovoltaic system. The attic is barely insulated. In the 1980s, some DIY work was started with insulation between the rafters, but it was abandoned halfway through. That insulation is still partly hanging there, tattered. The attic is suitable for expansion, but again, due to waning motivation from the owners, nothing was done.

The building savings contract now recommends adding insulation above the rafters to ensure sufficient summer heat protection (bedrooms are planned). After extensive research, I found some information about photovoltaic systems combined with above-rafter insulation, but only in cases where the insulation was already in place and the photovoltaic system was installed later – with discussions focusing on the more complex mounting on the roof structure.

But how do you proceed in the opposite case?: The photovoltaic system is already there, and then above-rafter insulation is added “underneath”? Has anyone had experience with this?

The photovoltaic system is over 10 years old, so it might be difficult to obtain the correct mounting materials if they have to match the exact installed type. Or is this standardized enough that I don’t need to worry?

Finally, I have another question on the topic: Online sources give very different estimates about the lifespan of concrete roof tiles. Lifetimes between 30 and 80 years are mentioned. When adding above-rafter insulation, would one generally always replace the roofing? Especially with roof tiles that are about 40 years old?

Thanks and best regards from
Pröter

What about using cellulose blown-in insulation as cavity insulation under the rafters?

Removing and reinstalling photovoltaic panels is not a special task; the mounts are generally universal. I would not choose lower-quality insulation just to save 2–3 days of DIY work.

Proeter schrieb:

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

No, unfortunately not. But with the ridiculously many ads, I’m just glad we don’t have to click after every single post at all...

Myrna_Loy schrieb:

What about cellulose loose-fill insulation as an insulation layer between the rafters?

According to the building savings contract assessment, that is not sufficient to achieve an adequate insulation value. And if the roof covering needs to be replaced anyway (the question about the lifespan of concrete roof tiles is still open), then from what I know, insulation above the rafters is significantly superior.

hampshire schrieb:

Taking down and reinstalling photovoltaic panels is not a big deal; the fastenings are usually universal.

I thought that would be more complicated. Thanks for the insight!

I agree with @hampshire that this should be doable. You definitely don’t have to replace the roof tiles, but after 40 years, I would personally replace them as well, especially since removing, carefully storing, and reinstalling them is probably more work than installing a completely new roof covering. Also, some tiles might be damaged, and you may not have enough extras. Ultimately, your roofer will need to advise you on that. If you go with new tiles, you could also replace the battens and underlay.

Inside, you probably don’t have planed rafters for an exposed rafter roof structure, right? How do you plan to handle that?

Proeter schrieb:

to achieve a sufficient insulation value

What insulation value are you aiming for? It also depends on the type and thickness of insulation you want to use; this has implications because it will increase the overall thickness of the roof. In our case, the energy consultant calculated 24cm (9½ inches) of PUR foam insulation—that’s quite a block! 🤨