i'm in the process of renovating a cafe/gallery. the building is 1
1/2 storeys and the upstairs is vacant at present but ultimately we
hope to open it up (coombed ceilings). however we are installing
heating downstairs and so i want to insulate the roof. i was planning
using rigid insulation above and beneath the rafters so i got in touch
with my local BC re ventilation. i was surprised to find out because
this is a commercial building the ventilation rules do not apply and I
am not obliged to install any. however I tend to think that these
guidelines are put in place for a reason and of course condensation
would be an issue so I DO WANT to ventilate but am just wondering what
a sensible solution would be. the rafters are at ~400mm (although
they do vary) centres and venting every bay seems excessive. There is
no soffit, I would get a vented ridge placed on the top so ventilation
would be required at the bottom of the roof.

there are probably 60 bays so i was thinking perhaps venting every
third and providing ventilation to the ones either side by drilling
holes through the rafters - would this work?

or because there is no soffit maybe removing stones (stone wall
exterior) from the top of of the wall.

any recommendations greatly appreciated?