ᐅ Photovoltaics – Should You Keep the Roof As Is or Wait?

Hello everyone, I am planning to install a new facade next year (ventilated facade with wood fiber and fiber cement) on a single-family house built in 1970. Everything is already organized and planned.

In the course of planning the facade (scaffolding setup), I thought about installing the photovoltaic system on the roof. There are several options, and the roofer says the tiles are probably still okay:

1. Photovoltaics on the 50-year-old tiles.
2. Re-roofing with new ventilation, no insulation – additional cost around $30,000.
3. Complete roof renovation including insulation.

Option 1 would just fit the budget, while I would have to wait a few years and rebuild the scaffolding for options 2 or 3.

I am a bit concerned about thermal bridges. The attic floor is unoccupied; the ceiling (ground floor roof) has additional insulation: 16 cm (6 inches) concrete, 2 layers of EPS, screed, and retrofitted with 12 cm (5 inches) Gutex wood fiber insulation and OSB boards for walking on. I have now measured the temperature; it is around 3°C (37°F) with 70% humidity. The joints between the OSB boards all look good.

An energy consultant warns about potential thermal bridges later at the facade-to-roof connection if the roof/exterior envelope is not insulated continuously.

So the question is – install photovoltaics on the roof now, or wait, save up, renovate first and then install photovoltaics?

Hello,
the mounts for the photovoltaic modules are attached either to the rafters or to the battens, depending on the system.
Therefore, the condition of the roof frame is the relevant factor, not the roof tiles.
Best regards, Joerg Klöcker

Makes sense, thank you. The roof structure is fine as long as you remove 1-2 tiles.
The attic floor is uninhabited. Last summer, I insulated the floor with 12 cm (5 inches) of wood fiber and installed OSB boards to walk on.
I measured with a hygrometer; under the roof, the temperature is always 2-3 degrees Celsius (36-37°F), and the humidity is at 70%.
Is this type of insulation sufficient for the next 15-20 years, or is it absolutely necessary to insulate the building envelope, meaning the exterior of the roof?

What type of roof tiles do you have, and what condition are they in? If you’re planning to install photovoltaic panels on top, the roof should be able to last another 20–30 years.

And your attic is just an unfinished loft, right? In that case, it’s enough to properly insulate the top floor ceiling (the floor of the attic). Insulating the sloping roof surfaces would be redundant since you’re already insulating the ceiling below. Depending on the exact construction, you might also need to add additional insulation where the roof structure rests on the walls.

The clay tiles are old but thicker than today's ones. So far, none have broken in 50 years (that's what I was told; I have only lived in the house for one year). The ventilation and roofing felt after 50 years are, of course, a concern, but so far the attic has stayed dry. If properly installed, don’t the modules also offer some protection to the tiles?

@WilderSueden has already mentioned that it is sufficient to insulate only the top floor ceiling. So go ahead with the photovoltaic system now. The conditions are currently improving significantly (feed-in tariffs, availability, prices). However, make sure to get several quotes, as the prices from solar installers can vary widely (easily a 50% difference for very similar performance).

If you later decide to insulate the storage area after all, it might be possible to do this from the inside. We did this using blown-in insulation (cellulose fibers), and it has worked perfectly for 15 years.