OSB panels for the attic "required", yet extra charge?

Unfortunately, not much remains, it is a 1.5-story building. But that's not so bad, since there is also a basement.

According to the email, they want to send me the structural analysis separately. If it really states that it is necessary, I will follow the advice and insist that it is included in the price.

Getting it brought up anyway is a tricky thing; they only thought of that kindly at the very last minute, the roof frame is planned to be finished today, then it will be closed up.

Sure, those few hundred euros don't make much of a difference anymore, but on the one hand, I find the approach not quite fair in principle and on the other hand, unfortunately, the "unforeseen" additional costs add up.

With us, the 22 mm OSB boards for roughly 100 sqm cost about 850 euros including [Märchensteuer] - so they were an extra item. For the fact that I didn’t have to buy, transport (without a trailer hitch or a small van/truck), and especially lift the boards up by myself, it was worth the price to me. However, for you, it’s quite a different matter. By the way, on the general contractor’s advice, we bought the boards directly through the carpentry company. They brought them along with the roof structure.

Regarding the statement about the statics, I can’t make sense of it. Maybe our mods and have some information on that.

Another point also makes me pause. Our general contractor explicitly advised us not to lay our OSB boards immediately because the house is still drying out (higher risk of mold formation). We were supposed to wait about one year, which we also diligently followed. This advice has been discussed earlier in the forum here and seems to be common practice.

Another point also makes me suspicious.
Our general contractor specifically advised us not to lay our OSB boards immediately, as the house is still drying out (higher risk of mold growth). We were supposed to wait about 1 year, which we bravely adhered to. This advice has already been discussed earlier in this forum and seems to be common practice.

This advice must absolutely be heeded. In our case, there was very slight mold on the ceiling in the attic during the first winter. It was the residual moisture, since on the one hand no more moisture was coming in, the attic is ventilated, and I couldn’t find anything with a thermal imaging camera either.
The residual moisture in new buildings is enormous, even if a ventilation system apparently suggests otherwise.

We have therefore deliberately installed tongue and groove boards instead of OSB panels. OSB acts as a vapor barrier.

We therefore deliberately installed rough boarding instead of OSB boards. OSB acts as a vapor barrier.

I have already read that in the mentioned thread. However, at that time the boards had already been installed and the house still had a year to dry out further. In addition, we left a strip of about 15-20 cm open all around and made the cutouts in the load-bearing support beams slightly larger. Thus, the attic is not completely sealed.

So far, in the last six months (after installation) we have not noticed anything in this regard.

ps: osb boards need a cross battens for air circulation underneath.

as already said on page 1: osb boards need a cross battens underneath so that air can circulate. then osb is not a problem after 1 year of drying. as soon as the attic is dry and ventilated once (wedges between the overlapping foils), nothing can happen anymore. if the real vapor barrier of the house (viewed from above under the insulation) is tight, no moisture can get into the attic at all.