Condensation problem in newly insulated loft space - Are the vents in the right place?

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Been doing some DIY in my loft - please be gentle! - I have made it into a room and insulated between/over rafters with celotex. I have some roof vents in place but there is a -pretty bad - condensation issue and I'm not sure the vents are in the right place. I will try and explain the construction as best as I can.

Please see the diagram attached.

Existing roof = Rafters 100mm, Bitumen felt, concrete tile
Insulated 50mm celotex in between rafters leaving a 50mm air space to the felt.
Celotex over rafters then plasterboard and skim
Storage from the purlin back to the eaves.
Tile vents x 4 installed by a builder on the 3rd course down from the ridge.
Plenty of ventilation at the eaves level from eaves vents and lap vents.

So when the access doors to the eaves storage are sealed closed there is a severe build up of condensation that seems to be running down the celotex from the upper part of the roof.

There is a small void that runs along the ridge probably about 10" deep. The tile vents are below this level and I feel they are maybe too far down the roof and so are not venting this void adequately?

Would taking a couple of the (cemented) ridge tiles off and moving these vents up as high as possible solve the problem, I am worried that the warm air is rising up into the void at the ridge and has nowhere to go?

What about ridge vents? Are they a thing for concrete tile roofs like mine?

Any help would be greatly appreciated!

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No it needs to be vented all the way along the ridge, otherwise the rafters will break the ventilation path.
 
No it needs to be vented all the way along the ridge, otherwise the rafters will break the ventilation path.

The ceiling is squared off for want of a better word And creates a void that runs the whole length of the ridge connecting all the rafter void?
 
Oh ok so the insulation is directly above your bit of flat ceiling (as per your drawing, should have paid more attention :rolleyes:) in which case you could try a few ridge vents and see how you get on.
 
Oh ok so the insulation is directly above your bit of flat ceiling (as per your drawing, should have paid more attention :rolleyes:) in which case you could try a few ridge vents and see how you get on.

Thanks a lot for your help! That's what I'm going to do
 
If you had properly sealed the habital area, and above the ceiling in the eaves void, then no significant warm air would be leaking into the gap below the tiles.
 
I did completely seal all the celotex with foil tape. The warm air will probably be coming through the storage area under at the eaves and through the access doors.
 

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