Timber frame extension to existing house - vapour barrier?

[Rick734]

Afternoon gents,

 

Been racking my brains on this one a bit and thought to turn to the helpful people on here. Who probably could run the country a lot better than the current shower. Anyway...

 

Stick-built TF extension on the side of my house, over the existing garage walls. Everything up, roof slated, external walls currently being rendered when weather permits. Now working on the inside on the first floor and my understanding is a VCL around the walls is a good idea on TF to prevent moisture moving into the timber frame from the inside - fine. I have myself some silver reflective VCL from Tradestore ready to go - but a couple of questions I've been thinking about:

1) How to seal the edges of it, where it meets the existing house - how much do I need to worry on this front. Can I just lap it over onto the render, run a bead of silicone down & tape over?

2) At floor level, is it just a case of taping it down onto the chipboard? Or is there some technical way to seal it? My brain says just seal it down and be done with it, but at the same time there is the ground floor below, so surely moisture could rise through the ceiling structure and get up into the wall structure...or is that just overthinking it.

 

I should add, I am more about speed and getting the job done at this point, rather than perfecting it. Definitely not a forever home and I'm in a hurry so not trying to spend time achieving microscopic increases in building performance...if that makes sense - quickest solutions that are acceptable, ideally!

 

Over to you! Image below of one of the vertical junctions where the TF meets the masonry...

 

 

Edited 4 hours ago by Rick734
Adding detail

[Rick734]

Further addition to the post...decided to have a bit of a chat with ChatGPT to get his views on the subject. The interesting bit was that when I mentioned I would be lining the internal face of the external walls with 18mm OSB (for fixing purposes), he/she/they/it decided that OSB can replace the whole vapour barrier/air tightness thing and is fine by itself...?! Sounds great, but I am cynical unless someone can weigh in on this please?

Edited 3 hours ago by Rick734

[JohnMo]

9 minutes ago, Rick734 said:

he/she/they/it decided that OSB can replace the whole vapour barrier/air tightness thing and is fine by itself

I wouldn't, OSB is vapour open.

 

Do it correctly install vapour barrier, tape all joints, 

1 hour ago, Rick734 said:

How to seal the edges of it,

Use something like this

https://passivehousesystems.co.uk/shop/adhesives-primers-sealants/fortax-6400/?utm_term=&utm_campaign=P-Max+Test&utm_source=adwords&utm_medium=ppc&hsa_acc=4901615203&hsa_cam=20355723828&hsa_grp=&hsa_ad=&hsa_src=x&hsa_tgt=&hsa_kw=&hsa_mt=&hsa_net=adwords&hsa_ver=3&gad_source=1&gad_campaignid=20364888406&gbraid=0AAAAApUFUNC26rUQyD2HwqFlOulMhVQWS&gclid=CjwKCAiAmKnKBhBrEiwAaqAnZ5CPWGBFVVio4GUfqzpKS1479NcoHwQrQVgTtExyEM110NUvopZ9HBoCl6AQAvD_BwE

 

1 hour ago, Rick734 said:

should add, I am more about speed and getting the job done at this point, rather than perfecting it.

Only one chance to do it right - slow down a bit.

 

1 hour ago, Rick734 said:

Definitely not a forever home

You never know what's ahead of you, you maybe their longer than you think and wish you had done a proper job.

[Mr Punter]

I understood that the OSB vapour openness can vary significantly by brand / batch, so I would polythene over this.  Quick to do with a stapler.  Run it down to the floor and trap it with the skirting.  Where are electrics going to be?

[Redbeard]

52 minutes ago, Rick734 said:

he/she/they/it decided that OSB can replace the whole vapour barrier/air tightness thing and is fine by itself...?! Sounds great, but I am cynical unless someone can weigh in on this please?

Exactly what I had in mind for my post-and-beam extn, but at a late stage the variability in quality of OSB in terms of air-tightness made me think again. I used Pro Clima Intello and taped all joints and perimeters to an obsessive degree.

[Tony L]

59 minutes ago, JohnMo said:

You never know what's ahead of you, you maybe their longer than you think and wish you had done a proper job.

 

This is my way of thinking, despite the missus wanting to be out as soon as we're safe from the hefty CIL fine.