Summerhouse roof ventilation

[Stringman_uk]

Hi all
The (external) build for my summerhouse is nearly complete and I am looking to move the build to the interior including insulation.

The summerhouse is of similar design to the one in the picture ( apologies to the original poster whose photo this is, hope you dont mind me borrowing it) but the roof joists are 6x 2
The idea is top ut 100mm pir in between the joists leaving a 25-30mm gap.
I presume it needs ventilation.
I want to box in the overhang with the T&G I have clad the shed with. and presume I should leave a ventilation gap.
Logic (to me) dictates the gap should be on the facing edge (marked in red) but I wondered if i could leave a gap on the downward facing edge( marked in blue)
The pir will end on the inside of the summmerhouse.
There will be a ventilation slot at the back in the same position as the red mark at the front.

Any Thoughts?

Thanks

 

[catlad]

Don't bother with any gap just fit it tight against the osb.

 

[Stringman_uk]

Don't bother with any gap just fit it tight against the osb.

Bit confused, as i want the joists hidden ( there will be wiring in between them)

 

[catlad]

How are you planning to hide the joists?

 

[Stringman_uk]

How are you planning to hide the joists?

cladding along the underside and the front facing vertical

 

[catlad]

If you want to ventilate your roof then it might be easier to counter your joist prior to installing the roof boards as it gives you more options for vents.

 

[Stringman_uk]

If you want to ventilate your roof then it might be easier to counter your joist prior to installing the roof boards as it gives you more options for vents.

Roof boards and epdm installed already. ( plus I dont really understand what you mean- sorry)
Really All I want to know is:
A: if I need to leave a ventilation gap as its a wooden shiplap construction so its not exactly airtight.

If I do

Does it matter which of my options in my original post I choose?

 

[catlad]

What I was trying to say is if you put your ply/ osb deck directly on to your joists you end up with a series of channels to vent, but if you get some rough sawn 3x1 and fix this counter to your joists you no longer have just a series of channels, so it gives you more options for venting. How much venting you require depends on how you are going to use the space.

 

[Stringman_uk]

Catlad, Ahh I see now.

During the summer it will just be used as a summerhouse, but during the winter it will probably be used as a daily home office as it will be so well insulated it will be warmer that the house!!!
There will be a 25mm gap (as per spec) between the osb and the pir insulation, and it was that I was looking at to see if ineed to leave a gap in my "boxing in"