Air tightness around floor joists.

[flanagaj]

I am going to be fitting the floor joists later this week and was always conscious that it's one area prone to significant issue when it comes to the air tightness test.  I have read about the 'Tony Tray' method and that certainly seems like a more reliable option than the joist end caps which still require a diligent brick layer and given we have different width joists, will probably be a faff to source.  It's a brick/block/full fill build up and was thinking that using DPC will suffice?

Is there any reason why you need to lap the DPC down the face of the internal blockwork.  So long as you have a full mortar course here, then air leakage will be negligible and you could trim flush with the wall?

I also see the term 'breathable' mentioned,  does that mean that I should not use DPC and should use another product?


 

[Redbeard]

1 hour ago, flanagaj said:

I also see the term 'breathable' mentioned,

 

Where? Not in this dwg, unless I am missing it.

[flanagaj]

35 minutes ago, Redbeard said:

 

Where? Not in this dwg, unless I am missing it.

Ok, not in that one, but it is here 

http://www.tonyshouse.readinguk.org/tonytray.pdf

[Russell griffiths]

With the amount of good flexible liquid coatings available I think I would forget the pain of the Tony tray and just paint around the joists when it is all up and the roof is on. 
you could spray airtight paint around them and that would get every nook and cranny. 

[flanagaj]

17 minutes ago, Russell griffiths said:

With the amount of good flexible liquid coatings available I think I would forget the pain of the Tony tray and just paint around the joists when it is all up and the roof is on. 
you could spray airtight paint around them and that would get every nook and cranny. 

After further research, that is what I have also concluded.  Given the likely shrinkage, it makes sense to do the final sealing one it's water tight and nicely dried out inside. 

[Oz07]

I think the tray is a good idea i have some leftover air tight membrane so will be trying it. I'd be wary or using dpc its not very flexible I don't think you'd get a great seal around it.  

Edited 2 hours ago by Oz07