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Hello We are in dispute with our builder, concerning the under-roof screen which we had requested at the beginning of construction, and he proposed us an OSB panel which for us seemed as much, see more effective. We had to call an expert because there are several problems of construction. This one found that the OSB panel does not go until the "sewer". Indeed it stops before the wall at the end of slope.It has no against liteaux.In case of leakage, the water would fall directly on the ceiling.The manufacturer explains that the OSB panel is not used as a rain screen and that if it does not go until down slope would be to allow ventilation.Il says it is not mandatory to have a rain screen. After doing multiple research with several organizations, such as APAVE, tile manufacturers (LAFARGE, TBF, IMERYS), architects.Some explain that a screen under the roof is mandatory and others tell us the opposite. We have obtained the DTU 40.21 NF P 31-202-1, but can not understand if this screen under roof is mandatory, and if the installation of the OSB is consistent. I specify that we are from Ile d'Oleron, that the house is located less than 5 km from the ocean and the slope of the roof and 30%. Waiting for your reply, thanking you, cordially

As a general rule, for classic blankets, the under-roof screen is not required, although it is considered as a "good practice" advised especially in mountain region to avoid the penetration of snow in the attic.
For roofs made of OSB (water repellent) for shingle installation, the screen is in principle not necessary since the shingles are by definition waterproof. Of course the panels must overflow, at the end, the sand pit or the bare wall, for connection with the gutter.

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