Placement of vent tiles

One tile vent would be enough fur 12sqm so I would say put 2 in each side but make sure they go in at different heights on each side for the airflow although there should be enough with vented eves and ridge have you checked the insulation is nit blocking the bottom vents

There is never a wright or wrong answer. But a combination of ventilation and insulation usually solves the problem. Condensation is caused when rockwool insulation is touching both roof felt and plaster, acting as a medium to transfer moisture between the two. A two inch air gap is required to allow moisture to flow away. Firstly, a rafter roll, witch fits over the rafters and underneath the roof felt (this prevents rockwool touching felt). Along with eve vents, is used on all new build sites and is building regs for new homes. Along with breathable membrain felt. The only time new builds have roof vents is for extractor fans for bathrooms or kitchens. Adding another roof vent could let more cold air and moisture in and potentially make the problem worse. Secondly, two inch kingspan insulation could be used between the rafters for extra thermal mass. This would allow the flow of air since rafters are four inch thick and kingspan is only 2 inch thick. And finally, as the roofers said above, a roof vent could be considered since old homes can behave in strange ways, but this tends to be an old school train of thought. And as i said earlyer, would never be found on new modern homes and in my experience of this method had made things worse. To summerise Rafter roll Eve vent strips Breathable membrain felt Kingspan insulation 2 inch air gap essential

Inbetween every beam, put one on top and bottom.

I would agree with answer 1 the vents that are already fitted should be sufficient I wouldn’t install any than two aside