Dry Ridge System & Loft ventilation

[Scott912]

I've got a standard trussed roof with sarking felt and wish to have the mortared ridge tiles replaced with the dry ridge system mainly because the mortar under the ridge tiles keeps falling away. Looking at the various dry ridge system manufacturers websites, they claim the dry ridge system improves loft ventilation (which would be an added bonus).

However, looking at some YouTube clips and speaking to a local roofer, the piece of sarking felt that overlaps the apex of the roof is not cut, removed or replaced during the installation of the new dry ridge system so I don't understand how loft space ventilation improves after fitting it.

Can anyone enlighten me?!

 

[RandomGrinch]

The Instructions for the kits tell you to trim back the felt to an appropriate distance.
The instructions are usually pretty good and available online.
See attached, 5 - 8mm gap left each side in this case.

 

[Scott912]

Thanks. 2 question then...

1. I've read the instructions for the Manthorpe system and they recommend 'when refelting the roof, leave a 5-8mm gap at the apex'. As my sarking felt overlaps the apex, presumably, there's nothing preventing me cutting this gap into the existing felt before installing the brackets?
2. I see the vent roll that is stuck on to the tiles has a vented mesh along its length - assuming I cut the 5-8mm gap in the felt, what prevents horizontal rain under high winds being blown up under the top tile, over the vent roll and to then seep into the loft space?

 

[RandomGrinch]

1). That's correct!
Also, in the case of retro-fitting, the brackets may be attached to the ridge board rather than the rafters. If this is possible, it may save removing the top row of tiles and battens.
2). I don't think anything will stop it in this circumstance. But the rate of leaks must be sufficiently rare for this not to be an issue. I may be wrong though!

 

[Scott912]

I think you're right. There's a British Standard BS 8612 for dry ridge systems and it suggests the system, if fitted correctly and accredited to that standard, is weather tight...

Many thanks.

 

[datarebal]

There are dry fix ridge and dry fix vent ridge systems . They are not the same

 

[Scott912]

Thanks but does either system preclude me from cutting the overlapping felt?
Also, what's the fundamental difference in each of those systems please?

 

[datarebal]

To vent you need to cut the felt