Still struggling… help please

[junglejim]

Still struggling with how to finish my osb cassette roof at the eaves….

 

Problems:

1. Drip tray: if it goes above the vent then the vent is basically useless. If it goes below then it will compromise the integrity of the drip tray.

 

2. Lower tiles support. I can see the advantage of supporting using the fascia but this doesn’t feel particularly good in terms of future proofing. If I need to replace the fascia then that would dislodge the bottom row of tiles. My solution is to add a lower batten at the bottom edge of the roof, supported by a fillet. This would also mean I can begin laying my tiles before installing fascia/soffit which I’m undecided on.

I’d like to get started on this to cover my roof but panicking in case I’ve missed something important or doing the wrong thing. I can see how the vent etc works in a roof with open rafters but struggling to see it for a solid roof.

 

 Thank you for everyone’s help.

 

ps. The images are me playing around with options.

[Mike]

10 hours ago, junglejim said:

My solution is to add a lower batten at the bottom edge of the roof, supported by a fillet. This would also mean I can begin laying my tiles before installing fascia/soffit which I’m undecided on.

Close.

 

Along the length of the fascia, roofing felt is traditionally laid on top of a timber 'tilting fillet' that supports the edge of the tiles at the correct height, and prevents the felt from sagging behind the fascia board. Modern high-performance felts aren't intended to be exposed to sunlight for extended periods, so will disintegrate where exposed at the eaves much faster than traditional felts. An eaves tray is fixed underneath the roofing felt to remedy this weakness, spanning over the top of the fascia board to discharge any rain into the gutter.

 

You need both the tilting fillet and the eaves tray to do the job properly, so that you can install / maintain / repair / replace the fascia without disturbing the tiles. On a solid roof, the tilting fillet goes on top of the counter battens, and you nail the eaves tray to the counter battens too. No need for an additional batten if the fillet is correct.

 

10 hours ago, junglejim said:

I can see how the vent etc works in a roof with open rafters but struggling to see it for a solid roof.

If you have over-facia vents, you'll need a 10mm / 25mm wide gap between the fascia and the tilting fillet (to maintain your 10,000mm² / 25,000mm² per metre ventilation) so that the air can get into the void between the counter battens under the felt. The eaves tray will be over the top of the vents, so won't be in the way.

 

[junglejim]

7 hours ago, Mike said:

Close.

 

Along the length of the fascia, roofing felt is traditionally laid on top of a timber 'tilting fillet' that supports the edge of the tiles at the correct height, and prevents the felt from sagging behind the fascia board. Modern high-performance felts aren't intended to be exposed to sunlight for extended periods, so will disintegrate where exposed at the eaves much faster than traditional felts. An eaves tray is fixed underneath the roofing felt to remedy this weakness, spanning over the top of the fascia board to discharge any rain into the gutter.

 

You need both the tilting fillet and the eaves tray to do the job properly, so that you can install / maintain / repair / replace the fascia without disturbing the tiles. On a solid roof, the tilting fillet goes on top of the counter battens, and you nail the eaves tray to the counter battens too. No need for an additional batten if the fillet is correct.

 

If you have over-facia vents, you'll need a 10mm / 25mm wide gap between the fascia and the tilting fillet (to maintain your 10,000mm² / 25,000mm² per metre ventilation) so that the air can get into the void between the counter battens under the felt. The eaves tray will be over the top of the vents, so won't be in the way.

 

Thank you for the detailed reply. That all makes sense but the membrane is beneath the counter batten so surely the vent needs to go above the eaves tray to enable clear airflow? 

[Mike]

6 hours ago, junglejim said:

That all makes sense but the membrane is beneath the counter batten

Check the manufacturer's installation guide / BBA Certificate to verify that that is permitted above OSB.

 

For example, when using Ply/OSB sheathing, Tyvek Supro says (the bold text is theirs)'These vapour resistant board materials do not allow adequate vapour diffusion and therefore should not be installed in non-ventilated applications above insulation. Ventilation at eaves and ridge and a continuous 50mm cross ventilation path must be maintained beneath the sheathing in accordance with the current version of BS5250.'

 

The only way of providing such ventilation beneath the membrane would be to install it on top of the counter battens.

 

Edited August 18 by Mike

[junglejim]

22 minutes ago, Mike said:

Check the manufacturer's installation guide / BBA Certificate to verify that that is permitted above OSB.

 

For example, when using Ply/OSB sheathing, Tyvek Supro says (the bold text is theirs)'These vapour resistant board materials do not allow adequate vapour diffusion and therefore should not be installed in non-ventilated applications above insulation. Ventilation at eaves and ridge and a continuous 50mm cross ventilation path must be maintained beneath the sheathing in accordance with the current version of BS5250.'

 

The only way of providing such ventilation beneath the membrane would be to install it on top of the counter battens.

 

Thanks Mike. Yes approved and have 50mm void beneath sheathing however I don’t think I need ventilation between sheath and membrane and I’m following timber frame guidelines on membrane on osb but it feels like a vent above the membrane and up between counter battens would be useful.