Underlayment damaged during re-roofing - how to respond?

Hello,

during the reroofing of our roof, the underlayment was torn about 30-40cm long as can be seen in the picture. Unfortunately, it is quite centrally located at the ridge of the hipped roof. I have read a bit, but opinions differ whether simply gluing is sufficient.
Since it is also new construction, so really fresh, I am not quite sure what makes sense. Basically, the scaffolding is still up.
How should one properly respond to this?

Thanks and regards

Simply have it glued on broadly from the outside (approx. 20cm overlap) with another underlay membrane. Ask the roofer to apply a primer (adhesion promoter) broadly, then stick on an underlay membrane and have the edges additionally sealed with vapor-permeable adhesive tape. This is permissible and does not constitute a defect. It occurs more often than one might think. It was the same in several places with wood fiber boards in our case as well. I contacted the manufacturer’s technical support and they confirmed that the repair is acceptable as is. It’s not a big deal since the underlay membrane is only supposed to serve a "temporary emergency function" in case of a leaking roof covering. The common misconception that this is a fully functional, permanent seal is simply not correct and not intended by the inventor.

Aha. It would be new to me that the underlay membrane only serves as an emergency function. The underlay membrane protects when rain is blown under the roof tiles by wind load or when snow lies on the roof and then melts. There is nothing "short-term" about it. If the underlay membrane is leaking, during heavy rain and storms it quickly pushes dozens of liters into the roof.

The underlay membrane is basically the raincoat... the roof tiles are the umbrella...

If rain or snow gets under the roof tiles, it's exactly such a situation, hence the quotation marks around the word. The rule should not allow this; if it does, then there is something wrong with the roofing. In the ZVDH regulations, the underlay membrane is designated as the "second water-bearing layer" and not as a seal. Wood fiberboards may be installed without an additional underlay membrane, but they only have a limited approval as an "emergency roof" for a few weeks. So why is it permissible to omit the underlay membrane when installing wood fiberboards, but the manufacturer only grants a limited weathering approval? Because that is simply not intended; the same applies to the underlay membrane. Ask a real roofer how long the underlay membrane will last if it is exposed to rain and snow EVERY time. By the way, they are not UV-stable in the long term either.

So the underlay membrane does protect against a few raindrops or some snow intrusion under the roof tiles during extreme snowstorms. But nothing more.

It is also not UV stable. After 3 months in the sun at the latest, it will break down.

Basically, it is very convenient for the roofer to work with underlay membrane. Remove the roof tiles, put on the underlay membrane, and the roof is waterproof for the time being. Otherwise, the roofers would have to re-cover the roof very quickly.

I also do not have any underlay membrane under the tiles of my barn roof. Was there ever moisture or snow behind the tiles? No. Everything is nicely sealed there.

By the way, on my house, I have installed a roof sheathing with boarding. So under my tiles on the rafters, there are complete boards, then the underlay membrane, and then battens and tiles. This has several advantages. On the one hand, it dampens noise; on the other hand, it is an insulating layer. And if the tiles ever fly away during a tornado, then I still have something underneath. Although that's actually nonsense.

As I said, basically you don't need an underlay membrane, but it's nice if you have it. In that case, just stick good tape over the crack and that's it. Not very pretty visually but functional.

In the past, when tile quality was significantly worse, there were also no underlay membranes. And still the roofs did not leak.