Breathable roof question

Hi all,
We're about to convert our loft, and if possible I'd like to avoid having to install roof vents.
The architect, has told us and building control that the roof is breathable - that is, that it is 110 years old and the slates are nailed directly onto the board - there's no felt. As such the roof is "breathing" already and the addition of vents will add nothing to the overall ventilation.
Building control want us to prove that the roof is breathing - or use vents. How do we prove that the roof is breathing? What kind of report do we commission to prove this?
If anyone has similar experience, or knows of online reports I'd be very grateful.
Many thanks in advance. Bob
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vents.
Take a photo from below, showing that there is no sarking or felt. Show photo to BCO.
Christian.
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Measure gaps between wood, multiply by total running length of board, see if it adds up to the magic number?
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Bob wrote:

Strike a smoke match in the loft and let the BCO see the smoke coming out of the tiles!
(I would have though that once he has seen there is no sarking etc then he should be happy about that aspect)
--
Cheers,

John.

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Thanks for the replies. I'm going to try the photo, measure gaps and negotiate route.
Cheers again B

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