Slate Vent Installed Incorrectly?

[Steebo69]

Hi, I'd appreciate any advice on this. Had some slate vents installed a few weeks back. We had some more work done the other day and somebody broke a slate next to one of the vents. This isn't the problem but what I saw beneath the broken slate could be as the sarking is visible. It's an old roof with no felt or membrane. Am I right in thinking both slates beneath the vent should have been cut to fit exactly around the vent box and up and under the slate above? So I shouldn't be seeing the sarking at all. Am worried the other slate beneath the vent might be the same, and the other vents as well. I've attached a pic.

Cheers for any advice.

 

[datarebal]

I don't think it's the correct vent anyway

 

[Steebo69]

Thanks, can you tell me why it's not the correct vent?

 

[catlad]

What makes you think you need more ventilation?

 

[datarebal]

Because it's not .it has been made to fit