Existing Roof and PV Retrofit: The Starting Point
More and more homeowners and businesses are retrofitting existing buildings with PV systems. The roof was not designed for PV cables — there are no pre-prepared penetrations, and the tiles may be old and brittle. This article is aimed at electrical companies and solar installers who regularly undertake retrofit projects.
Step 1: Inventory and Cable Routing
Before lifting a tile, the cable routing should be determined:
- Where is the inverter located? (Basement, attic, exterior wall)
- How many cables need to be routed?
- Are there existing openings that can be used?
- What is the condition of the tiles?
Step 2: Choose the Right Penetration Point
For retrofits, ideally choose the point:
- As close as possible to the inverter location (short cable runs)
- Under a ridge tile or in a spot with a robust underlayment
- Not in the area of valleys or other water entry points
- Accessible for later maintenance
Step 3: Remove Tiles and Install Penetration
- Carefully lift tiles at the planned spot — with caution on old roofs
- Check the underlayment: Seal any cracks or defects beforehand
- Cable routing through the underlayment: Cut a slit, insert the cable, seal with bitumen tape
- Place the roof penetration over the cable and secure it
- Replace the tiles
Typical Mistakes in Retrofits
Mistake 1 – Multiple cables in one opening: Leads to cable pinching and makes proper sealing impossible.
Mistake 2 – Underlayment not sealed: Moisture in the roof structure only becomes visible after years — but then it's expensive.
Mistake 3 – No mechanical cable protection: Cables directly on the tile are damaged by thermal expansion and friction.
Conclusion
Retrofits are successful with careful planning and one cable protector per penetration. Our PV cable roof penetrations in 105 mm, 125 mm, and 150 mm are abrasion-resistant, UV-stable, and Made in Germany. B2B volume pricing from 20 pieces.
You can find suitable PV cable roof penetrations as mechanical abrasion protection in the D24-B2B Shop (volume pricing from 20 pieces) – UV-resistant TPU, Made in Germany.
