Thickness of installation plates for attic?

I had the roofer lay appropriate battens for the counter-battening and OSB boards in sufficient quantity onto the framework while constructing the roof truss. This is much easier than carrying the boards and battens up later through the loft access hatch. Unfortunately, at that time I did not yet know that tongue and groove boards are better.

I attached the counter-battens to the framework at intervals of about 50cm. On one side, I then laid the OSB boards up to the loft access hatch (about 30% of the attic). Around the edges (i.e., near the masonry), I left about 5 cm of space so that air can circulate. After one year, the existing space is still more than sufficient. Therefore, I will only install the other boards when I need more space.

Regarding thickness: our OSB boards are 22 or 26mm. They easily support the stack of spare tiles.

Edit: We have no mold.

Edit: We do not have mold.

However, you have also installed counter battens so that air can circulate underneath and have only surfaced 30% so far.

Let's ask it the other way around.. what speaks against [Rauspund]?

I am facing a similar question. For the roof sheathing, I have already chosen tongue and groove boards because they "breathe" better, and I will probably also use tongue and groove for the attic. However, I see the following error in the logic behind this: Under the insulation there is a vapor barrier, so a minimal ventilation upwards (as with joists) should easily suffice, right?

The advantage of OSB is probably the much faster and easier installation. The surface is likely also more even, so a higher-quality flooring can probably be laid on top later.

Question: Should a counter batten also be laid under tongue and groove boards, and if so, why?

Normally, there is a vapor barrier under the insulation. The only question is whether it is 100% airtight. At least in our case, the vapor barrier is fixed to the walls. In this respect, moisture could rise up through the walls. Besides that, you also have cable penetrations, wall connections, and seams/holes in the foil, where there is a risk that it is not 100% airtight.

Under the insulation there is a vapor barrier, so a minimal ventilation to the top (like with Jochen) should be more than enough, right?

IMHO: Hardly any moisture will penetrate from the house into the insulation (since the house is airtight), but the insulation, despite OSB boards above, is exposed to the atmosphere and eventually somewhere the dew point will be undershot (at night, weather change) and once you have mold inside ...