Airtight around joists?

[DragsterDriver]

Evening

my timber frame, I believe the order of materials to be:

cladding

25mm batten

breather membrane 

osb 

145 cls stud containing 140mm frametherm.

 

then inside:

 

50mm pir board?

25mm service batten

plasterboard.

 

the inside layers is maybe the ‘grey area’ for me, certainly where I would put the  airtight layer?

 

also- around the joists, fold a strip around the end during construction or cut around afterwards?

 

joists like this but not the passiv wall.

 

 

 

[Olf]

Tony tray

14 minutes ago, DragsterDriver said:

certainly where I would put the  airtight layer?

Like on the drawing, first layer on the OSB

 

14 minutes ago, DragsterDriver said:

fold a strip around the end during construction or cut around afterwards?

Do a Tony tray trick : continue the membrane under the overhang and then over with the same continuos piece of the membrane. Cutting and sealing around joists is a bitch, hours of faff with the tape not worth £5 spent on extra stretch of the membrane.

[DragsterDriver]

19 minutes ago, Olf said:

Tony tray

Like on the drawing, first layer on the OSB

 

Do a Tony tray trick : continue the membrane under the overhang and then over with the same continuos piece of the membrane. Cutting and sealing around joists is a bitch, hours of faff with the tape not worth £5 spent on extra stretch of the membrane.

Ah - Tony Tray sounds like what I had in mind  

 

I won’t have the internal osb layer so airtight over the studs, behind the pir and service void  

[Olf]

On 08/11/2021 at 21:09, DragsterDriver said:

I won’t have the internal osb layer

Make sure removal of OSB skin will not affect structural properties of the wall, it may be there not only to keep the cellulose in place

[Dudda]

Internally I'd go 50mm PIR fixed to the 140mm timber frame, airtight vapor layer, 25mm battens and then the plasterboard.

 

You don't have to have OSB on both sides. You do on twin stud walls and in some other cases but if you've only a 140mm stud then you generally don't need it. Obviously check with your engineer. The reason I'd go this route with the airtight vapor control layer is you can see it and patch it. eg if an electrician drills a hole for an external light you can seal the penetration or if an area wasn't taped correctly you can easily see and repair it. If you use an internal OSB layer as the airtight layer, then have PIR and the battens forming the service cavity you'll have to rip a chunk of the PIR off to enable you tape the electrical cable to the OSB or repair the poorly taped joint, etc. Also the airtight vapor control layer is a lot cheaper than an additional unnecessary layer of OSB.

 

As a separate item I'd consider 35mm battens otherwise wider battens if using 25mm eg 65x25. When overlapping two sheets of plasterboard you're adding a lot of screws and the thin batten can split. It needs a bit more rigidity as it's the 50mm PIR between it and the main timber support structure. 

Edited November 10, 2021 by Dudda

[DragsterDriver]

On 10/11/2021 at 09:57, Dudda said:

Internally I'd go 50mm PIR fixed to the 140mm timber frame, airtight vapor layer, 25mm battens and then the plasterboard.

 

You don't have to have OSB on both sides. You do on twin stud walls and in some other cases but if you've only a 140mm stud then you generally don't need it. Obviously check with your engineer. The reason I'd go this route with the airtight vapor control layer is you can see it and patch it. eg if an electrician drills a hole for an external light you can seal the penetration or if an area wasn't taped correctly you can easily see and repair it. If you use an internal OSB layer as the airtight layer, then have PIR and the battens forming the service cavity you'll have to rip a chunk of the PIR off to enable you tape the electrical cable to the OSB or repair the poorly taped joint, etc. Also the airtight vapor control layer is a lot cheaper than an additional unnecessary layer of OSB.

 

As a separate item I'd consider 35mm battens otherwise wider battens if using 25mm eg 65x25. When overlapping two sheets of plasterboard you're adding a lot of screws and the thin batten can split. It needs a bit more rigidity as it's the 50mm PIR between it and the main timber support structure. 

That’s how I see it- wondering now about the ‘Tony tray’ around the joists before the 50mm pir board ??‍♂️