Eaves ventilation - what size vent per rafter

[OscarWilliams]

I’ve put some ply boards down between the rafters to fill the eaves space and left about an inch gap for airflow - I will then cover this gap with insect mesh (sealed and stapled). 
 

The building in question is a 200 year old barn that’s recently received a new roof - I’m not interested in contemporary ventilation systems - plastic vents etc. 

 

Its unconventional but I’m confident the concept is sufficient (and nicely uses left over ply)...question is how bigger gap should I leave? The more airflow the better but the less heat efficient. A 1 inch gap at 14 inches long is the equivalent to there being a square hole 3.75” x 3.75” for each rafter (14 sq inches). 

My guts telling my it’s fine but I’m tempted to make the gap 1/2” bigger!

 

Thoughts on this? Any formulas to work this out?

 

Thanks in advance, 

 

Oscar 

Edited February 24, 2021 by OscarWilliams

[Conor]

The guidance in normal circumstances would be equivalent to 25mm continuous ventilation. So if you are leaving a gap for half of the continuous length, it would be 50mm wide.