Cold roof ventilation with cantilevered joists?

[houstonwehaveaproblem]

I have a garden room which I’m in the process of building.

I have decided to go down the cold roof design. I can achieve 50mm ventilation front to back of the building as the joists run in that direction however I have a side overhang which has been built by cantilever off the front to back joists.

I will need this section to be ventilated but the only way I can see of doing this is by drilling the joists for cross airflow but a 50mm hole in the joist is going to weaken the joist?

Any advice.

Thanks

 

[catlad]

Not sure I completely understand!
But a good way to achieve cross ventilation is to lay some timber perpendicular to the joists before fitting the roof deck. 3x1" rough sawn will do.

 

[Bouy]

my advice is draw us a sketch of whats what