'Eaves' ventilation where a pitched roof comes off a flat roof

[PeCos]

Hi all, we have a cold pitched roof with 1F felt coming off warm flat roof area on a new build.
The architects plans show roof vents which would need to go in every other rafter, I'm concerned about so much cutting of the felt and the fact it's only every other rafter so not continuing ventilation.
The roofer has suggested a fillet and 20mn vent but this leaves only about 75m.lap of tiles to EPDM and the bottom two courses of Rosemary tiles are very flat (roughly 10 deg)- but vent would be continuous.
The only other option would be to fit a 5mm abutment flashing detail which is probably a bodge up. What do people think is the best option?

 

[noseall]

What do people think is the best option?

TVT's as shown. No big deal. Depending on the tile, they can be quite discreet too.

 

[^woody^]

Use a membrane that does not require additional roof void ventilation.

 

[noseall]

Use a membrane that does not require additional roof void ventilation.

I doubt one exists to deal with all scenarios. Even Tyvek have had issues.

 

[^woody^]

I doubt one exists to deal with all scenarios. Even Tyvek have had issues.

Any membrane that is defined as air and vapour permeable would perform without additional venting. A BBA certificate would certify this and it would be acceptable to building control.

The advantage of such a membrane is that it helps with complex shaped roofs - and even normal roofs as tile vents part way up the slope do not provide full air movement to all parts of the roof void in any case.

Proctor Air, Permavent Apex, Klober Permo Air, DuPont Tyvek are some examples.

 

[noseall]

Any membrane that is defined as air and vapour permeable would perform without additional venting

No, they do not.

. A BBA certificate would certify this and it would be acceptable to building control.

I'm not arguing whether they pass BC scrutiny, rather I'm just stating many don't perform well under extremes. We always supplement our breathable membrane with (OFV) vents.

The advantage of such a membrane is that it helps with complex shaped roofs - and even normal roofs as tile vents part way up the slope do not provide full air movement to all parts of the roof void in any case.

Proctor Air, Permavent Apex, Klober Permo Air, DuPont Tyvek are some examples.

Yes, I named one of the (troublesome) premium brands in my post.

 

[^woody^]

Condensation is not the issue.
Even a vented roof void will get condensation. Vents are a relic from the days of bitumen felt - which seals the roof void.

The requirement is that any humidity is controlled and condensation allowed to evaporate away naturally via normal air movement. The AO membrane and sags at the laps does this.