Block built or timber frame extension. Vapor barrier

[2020c]

I'm still deciding on which to do for an extension. Either block built or timber frame.

I'll be doing a warm roof with 140mm insulation. The vapor barrier on top of the 18mm osb board under the insulation. One thing that has been bothering me is the vapor barrier on the inside of the timber frame which will be over the insulation and under the plasterboard. When I come to ceiling height where it meets the joist, do I continue the vapor barrier on up to the underside of the osb board just stop at ceiling height.

This is one detail I can't find much information on the internet about. This is one detail I'll need to get right because after it's all plastered up and roof on, there's no going back. Would hate to do all this work then the moisture escaping to the underside of the osb board and creating sweating and ruining all my efforts. Everything else on the extension is straight forward for me however this is one detail I need to know before I proceed.

 

[^woody^]

You would have to detail it so that no moist air can get into the frame from the ceiling void. There will also be a ventilated cavity for for the frame

 

[2020c]

You would have to detail it so that no moist air can get into the frame from the ceiling void. There will also be a ventilated cavity for for the frame

I installed some timber frame houses before, frame, block,roof years ago then handed them over for the other trades to take over. Weepholes will be going in along with venting. I have even 4 building regs books I follow anytime I need to look something up however this one detail isnt on it or isn't much in it online.

I found this video of a timber frame built although this is a garden room, the same principles apply. 11.45 is when he talks about different types of vapor barrier, 12.50 what he using and 15.00mins is of where the detail I'm wanting to know about. He says not to worry to much but I'm not too sure.


https://www.google.com/url?sa=t&source=web&rct=j&url=https://m.youtube.com/watch?v=C-eVlYsZ3iQ&ved=2ahUKEwiBqrua_KXvAhV9ShUIHXwTDo0Qo7QBMAF6BAgIEAE&usg=AOvVaw33WOfNk1vcYHc_hvUBYAQj

 

[^woody^]

From Timber frame Construction by TRADA.

But I would lap the frame vapour barrier horizontally over those top two timbers you can see in the fame there

 

[2020c]

From Timber frame Construction by TRADA.

But I would lap the frame vapour barrier horizontally over those top two timbers you can see in the fame there

View attachment 226013

That picture wouldnt be all that great, although the wording of it is what i needed. Thank you woody! Heres hoping other members on here will come long with detailed pics of this detail of them doing it before.

 

[2020c]

Not my picture! Looking at this, its going to be a tedious work installing the vapor barrier up between these joists if theres no other way around it!

Would any member have any pictures of previous work of this detail.

 

[2020c]

i am answering my own questions here but something that i just found that i thought id post here for anyone needing this information in the future.

See video for the detail im looking.