junglejim

Thanks. Because the roof is a cassette system sheathed in OSB I need to ensure airflow between rafters (soffit vent) and also above the osb and membrane (between counter battens) hence the over fascia vent being above the drip tray. Or at least that’s my understanding.

This is what I’m thinking at the moment so wanted to check for advice… The vent strip seems a bit unnecessary but think it might be something that BC want to see. Any thoughts/feedback welcome

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.

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?

Thank you. That’s a really helpful picture... couple more questions if that’s ok? 1. does that mean screwing through the membrane and tray? Is that a possible problem for water ingress? 2. That vent looks much better… yes mine is a corner one … will have to see if the store have anything else. 3. I notice you’ve cut the counter battens short… I’ve realised that I’ve come too far down and just started cutting back to enable membrane to lift. Presumably you continued cutting them back all the way along. 4. Sub Fascia: nice chunky piece of wood… tempted to do similar as have lots of rafters left over… architect specified ply but can’t see why not use timber. however I’m reluctant to sit tiles on incase I ever need to take off. I was going to create a short fillet and run an extra batten along the bottom edge to do this instead although thinking about it if the vent is also attached I won’t be able to remove anyway. (Hmm) also my tiles have ridges in which I assume is to enable ventilation as there are clear channels when it is sat on the batten. I feel like BC might insist on a vent strip though? Thank you… any more pics/advice greatly appreciated as having a bit of a struggle with this.

Thank you. However my batten space is above the membrane as roof is osb. So when I run membrane/tray over the vent they would be in the way.

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.

On closer inspection I’m not sure an eaves vent is even necessary given that the tiles have ridges in the bottom which essentially do the same but should probably include as per BC spec any way. Any more thoughts??

Yes agreed… this is my quandary. But does having the vent beneath the tray and membrane affect air flow?

Thanks… does that not compromise air flow between the counter battens? (Sheathed osb roof) @nod

Trying to figure out from this picture which side of the air vent the tray goes.

This is what it looks like above the drip tray but screw holes would comprise the tray and would also make replacing the fascia very difficult if needed in future. However I’d the vent goes underneath then the tray/membrane will be blocking the air gap between counter battens

Trying to figure out whether the drip tray can go over the above fascia vent. That seems to fit together easiest but would seem to block free flow of air between counter battens. Roof: osb - membrane - counter batten - tile batten

Hoping someone can offer some advice? 🤞

I’m hoping someone can offer some advice. I’m a bit confused about the fascia detail and order of layers on a cassette roof. my layers are: osb cassette - breather membrane - counter batten - batten at the eaves I have rafter ends - battens - fascia with a fascia vent above and a drip tray tucked under the membrane. I’m trying to work out how to ensure any water has a smooth run over the fascia. 1. Should counter battens go all the way to the edge of the cassette? 2. Does the drip tray go on top of the over fascia vent or underneath? 3. Usually the fascia would be pushed up to the underside of the tiles but I would have thought doing that in this instance would force the membrane uphill. The only way I can think to negate this is to finish counter battens early. I feel like I going down a rabbit hole and there must be an easy solution. Hopefully someone can help. Many thanks

Trying to find out the optimum nail spacing for vertical counter battens fixed to rafters. I’m thinking 400mm ish?

Ps. In this diagram the fascia is flush to the roof sheathing… this would seem to make sense as the breather membrane is below the counter battens so wouldn’t want to create a lip that could trap water. Am I right with that?

I’m preparing to roof my timber frame build. The rafters are up to 15mm different in distance from the wall. I’m unsure how to proceed with sub fascia and/or fascia to ensure everything is level and ready for the roof. I’m tempted to go for wood fascia/soffit rather than covering in pvc. 2 problems I have: 1. Rafter lengths up to 15mm different 2. osb overhanging rafter slightly so attaching directly to rafter would result in tilt. A few other notes: I haven’t clad the walls yet. I’m unsure whether I can get away with tiling the roof first but realise it will be easier if the fascia is on. i could trim the osb so that I can fix directly to rafter ends. I’m unsure dimensions of wood needed. Any tips greatly appreciated as always.

Thank you that’s helpful

Thanks that sounds like a good solution… can you suggest a grout?

That would be logical but they’ve finished on site!

Just spotted this on my newly erected timber frame build and wondered if I should be concerned? Surely there’s a neater way of doing this… slight worried that BC might have an issue? Thanks

That’s helpful. Yes I was wondering about the width because larch is generally narrow.