Air-tightness and wall plates (rim joists)

[ToughButterCup]

Sometimes you bump into really interesting stuff online..... like this  (scroll down to the section headed Wall-Plate)

Here's the relevant passage

'...In order to make the house air-tight, the wall plates have been installed over a polythene membrane, which is shown tacked down until the construction has proceeded to the point where it can be folded up and over the plywood which will soon cover the ends of the joists. Ultimately it will seal against the plywood decking which will be laid on top of the joists....' (https://edinkist.wordpress.com/diary-of-the-build/)

 

To ensure air-tightness at the wall-plate roof interface, is this method (putting the wall plate on top of a polythene membrane) common? 

 

I feel some phone calls coming on.

[MikeSharp01]

19 minutes ago, recoveringacademic said:

To ensure air-tightness at the wall-plate roof interface

This will depend, one guesses, on where your air tight layer is. If on the inside of the Durasol and not including the roofspace then you might run the membrane under the roof joists, if above then the joists need to be included so you need to go around the ends but that also means a messy junction unless you go up and over the trusses with your air tight membrane. IIRC your internal floor / wall junction has something like it. I guess if you go this way then keeping the membrane out of harms way while the roof goes on.

[Ian]

@recoveringacademic

I think the idea originally came from

Tony Cowling as the "Tony Tray":

http://tonyshouse.readinguk.org/tony.htm

 

Edited March 9, 2018 by Ian

[ToughButterCup]

1 minute ago, Ian said:

@recoveringacademic

I think the idea originally came from

Tony Cowling as the "Tony Tray":

http://tonyshouse.readinguk.org/tony.htm

 

 

Yer a star! Cheers!

Ian

[Jeremy Harris]

Yes, definitely a "Tony Tray", but there is another method available in the US that looks like it could be useful if it ever comes over here: http://aerobarrier.net/

 

They have an interesting video showing how it works:

 

 

[Ian]

@recoveringacademic

The main commercial alternative is using joist caps but they are more expensive and not as good:

https://www.wickes.co.uk/Wickes-Safety-Fast-Joint-Cap-SFJC305-50/p/215030

[ToughButterCup]

Thanks very much indeed. .....

Ian

[ProDave]

Our builders used the same method to endure the air tight membrane went around the ends of the joists, though they did not know it as a "Tony tray"

[ToughButterCup]

I'm bumping this because I have a piccy or two for ya.

 

I have mocked up my Tony Tray thus : taking a sparrow's view along the wallplate....

 

 

and from the outside it looks like this

 

My chippy (very nice man, very very nice man) hasn't seen a Tony's Tray before (well that makes two of us). And as I suspect there are more than just two of us I thought I'd write this post. This is the original article which for members considering Durisol will be of interest.  (scroll down to 'wall plate' ) It illustrates the concept of wrapping the ends of the rafters in polythene. I wish the author had done a before and after shot.....

 

The chippy's question was: Do we seat the wallplate  and plastic sit on top of a layer of mortar as usual to ensure the wallplate is level? 

Of course I didn't know (what do you expect?) My instinct says  yes  because there's no point in a wonky wall plate is there? The architect says the wall plate must be anchored to the concrete core. Quite how isn't specified.

This where I found the idea

• Do we bed the wall plate and plastic on mortar?
• How do we fasten the wall plate to the concrete core? Top- down, or with wall straps? Or both?

(PS, the forest of KwikStage standards were erected by yours truly, now past master and lone scaffolder - got the bruises to prove it)

[bissoejosh]

Watching with interest as this is my job next week on our first floor joist wall plate. I was planning (until someone says otherwise) to use mortar & straps for the wall plate, then airtight membrane over the top of the plate but under the joists which sit on top thus making the wall plate 'outside' as such. Perhaps I should be doing the same as you and have the membrane beneath the wall plate.

 

Curious to see the thoughts of others...

[Construction Channel]

I would say you have got to bed the plates ( for our BCO you definitely would,)

 

having never done it I can only speculate but I reckon I would bed both down, mortar / plastic/mortar/ wood leave that to go off, then screw it down,

 

you probably could get away with just straps but i don't like the idea of it, normally we would use concrete screws but as you are looking for airtightness it might be better to use a nylon plug (the big grey ones) as that will expand a bit and fill any voids, 

 

you will definitely need straps for regs but it brings a whoole new issue of whether to VCL before or after the straps, 

 

before means, you can have a continuous VCL going up the wall and out over the rafters but you get all the fixing holes to contend with (probably how id do it then tape over the while strap)

 

after means, you don't get any fixing holes but there will be a joint in the VCL at plate height you will need to tape and a strap in the way  that you would need to seal around somehow.

 

 

have you decided on the airtight layer for the walls yet as that may have an impact on the decision, 

 

[ToughButterCup]

38 minutes ago, Construction Channel said:

I would say you have got to bed the plates ( for our BCO you definitely would,)

[...]

but it brings a whole new issue of whether to VCL before or after the straps, 

[...]

have you decided on the airtight layer for the walls yet as that may have an impact on the decision, 

 

I'm finkin'. 

Loads of reading to do....

[RichS]

I always assumed that the air tight membrane would go underneath the rafters and then lap down and be sealed onto the internal wall face. Doing it this way it wouldn't go anywhere near the wall plate.

Am I missing something??

[bissoejosh]

I agree with @RichS. This is normally only an issue for floor joists at 1st floor level where they have to protrude outside of the airtight layer.

 

@recoveringacademic on your build the parge coat / plaster is your airtight layer I think? This would therefore be on the inside face all the way up the wall to rafter level meaning the roofing airtight membrane can sit under the rafter and be bedded into the wall face as suggested above. This would all be inside of the wall plate I think.

[ToughButterCup]

22 minutes ago, bissoejosh said:

[...]

@recoveringacademic on your build the parge coat / plaster is your airtight layer I think? This would therefore be on the inside face all the way up the wall to rafter level meaning the roofing airtight membrane can sit under the rafter and be bedded into the wall face as suggested above. This would all be inside of the wall plate I think.

 

Exactly. But in this process  is, for me, just-in-time-learning. I really do not know what I am doing - but I do understand the reasoning behind it.

I am also parging the outside of the building as you can see above. A la @Nickfromwales belt and braces job.... 

The strong cross-light in the photo emphasises the outline of the blocks.

37 minutes ago, bissoejosh said:

[...]

meaning the roofing airtight membrane can sit under the rafter and be bedded into the wall face as suggested above. 

[...]

 

So easily said. But.

Quite how I am going to get a sand and cement parge coat to stick to the plastic inside the wall I don't know. It was drafty here yesterday, so I couldn't  photograph the membrane on the inside of the wall (It was flapping about). I'll try and take a photo today to illustrate the point.

(And I thought I was retired, this is just like being back at work, but in this case the only line manager is an accurate cost-to-completion spreadsheet)

[bissoejosh]

For the link between membrane and plaster I was going to use something like this, as although I’m using it on a different element of the build to you the principle is very similar...

 

https://proclima.com/products/bonding-agents/contega-pv

 

My understanding is it sticks to the membrane on one edge and the other can be plastered over.

Edited April 6, 2018 by bissoejosh

[ToughButterCup]

Thanks. Yer a star @bissoejosh

I'm going to use this weekend to do some thorough research into the detail of how, where, and how much. The YT videos point to the tape being made in Germany.

Vorsprung durch Technik and all that. There's very little stuff in our build that can't be traced back to Tchermanee. 

[bissoejosh]

This might help further. You can do final plastering etc at a much later stage once the shell is sorted.

 

http://passivhausrefurb.blogspot.co.uk/2011/02/

 

 

[bissoejosh]

Did you get this done in the end? What did you use for your airtight membrane as I need to get mine ordered.