Ventilate walkable attic?

Hello.

We have the following roof construction:
External rafter insulation 52mm and insulation between rafters 280mm.

In the collar beam level, an [einschubtreppe] is to be installed. The access is only for inspection and for storage of things that will not be needed for years, e.g. leftover tiles, etc...
So not much moisture will probably be brought in.

Do I still need ventilation for the attic? The carpenter would install [Sanilüfter], the site manager thinks it is unnecessary.

Thanks for advice.

It is unnecessary if basic principles of building physics are observed.

On a cold floor, temperatures fluctuate greatly over 24 hours due to solar radiation. This means that the air on the cold floor can absorb more or less moisture at different times; therefore, the air on the cold floor should be dry enough so that no condensation occurs even at night.

This means the retractable ladder should only be left open for as short a time as possible, then nothing will happen on the floor.

Storing tiles in the attic? Is it normal wood up there with you? Please remember that it should usually not be more than 100kg-150kg.

So we can store over 1000 kg per m2 on our collar beams.

Regarding the topic: I would definitely provide ventilation. From my own experience, I know that unplanned moisture ingress can indeed occur, especially during the construction phase. In addition, the vapor barrier is never 100% tight.

We have two Velux windows installed and the ridge line is open.