To provide ventilation opening points can usually be provided on the following areas of a pitched roof.
Slate roof ventilation requirements.
The ventilation requirements may vary based on the circumstances of the building.
Matthias in my judgment you can skip the ridge vent.
Slate vents are by far the easiest professional solution to roof ventilation problems.
As you noted slate roofs tend to allow air movement through the slates.
Roof voids must be ventilated in order to stop warm air condensing on cold surfaces.
They are super easy to fit either for new roofs or renovating an existing one.
Eaves soffits and fascias.
The air gap dimensions shown on the drawings are the minimum widths required for clear continuous ventilation air paths at the eaves.
To comply with the code of practice for control of condensation in buildings bs 5250 2011 a1 2016 and the nhbc roof vents should be installed at both the eaves and ridge level.
Additional ventilation at or near the ridge equivalent to a 5 mm continuous vent is required in the case of warm roofs and is also recommended if the case of cold roofs if pitch of the roof is greater than 35 or if the span is greater than 10 metres.
It s said that one of the best places to fit slate roof vents is normally the bottom third of a roof just above insulation level.
Duo pitch roofs greater than 200 pitch or greater than 10m span should have additional ventilation at the ridge to assist airflow through the roof void equivalent to at least a 3 mm wide continuous gap.
Moreover slates are vapor permeable so moisture problems at the sheathing layer are highly unlikely.