Airtightness of first floor void

[WWilts]

For various reasons constrained to use drylining of external walls. Trying to achieve as much airtightness of first floor void as possible, on a budget. Apologies in advance to Tony for taking liberties with a perfectly good concept.

 

Qus:

1) How can the Tony Tray concept be made to work with plasterboard on adhesive frame? Builder not familiar with this approach. Trying to draw polythene version for him (see pic)
2) How does the polythene airtightness barrier cope with the weight of blocks above? (3.6N aircrete holding up large roof trusses)

3) How would you draw the junctions between the polythene in the joist openings and the polythene over the infill blocks?
4) Is a DPC used below and/or above first floor joists? If so, below or above the airtightness barrier (visualising piercing of the polythene by rough mortar)

 

 

 

 

[WWilts]

further attempt

Might frighten the poor builder off

[Mr Punter]

You can get joist pockets for built in joists.  I have never used them so cannot vouch.

[tonyshouse]

The problem with them is leaks round them and all the other leaks between blocks etc. 
 

I would worry about plasterboard on battens becoming a ‘plasterboard tent’ cold air in the void, high air leakages 

 

I don’t use poly, usually an air tight membrane, gravity is very good at stopping things moving and once trapped weight holds everything in place 

 

if you draw a pencil line from the tray to the airtightness layer in the wall do they join? 

[WWilts]

18 minutes ago, tonyshouse said:

if you draw a pencil line from the tray to the airtightness layer in the wall do they join? 

Plasterboard with taped junctions intended to be the airtight barrier. Tray taped to plasterboard.

[tonyshouse]

Then cold air/wind will most likely be able to get into the void behind the plasterboard  ?

[WWilts]

5 hours ago, tonyshouse said:

Then cold air/wind will most likely be able to get into the void behind the plasterboard

Yes that air will be colder than room temperature. But hopefully the bonded EPS in the cavity will help that air to retain some of the room heat. And the beads will hopefully keep the wind out, when it penetrates the brick. Air is reputed to be a decent insulator (EPS beads are 98% air).

All this to console ourselves for using drylining rather than wet plaster.

Still trying to draw the details so that I can explain clearly to the builder. Danger is that my drawings will become the problem rather than the solution.

 

 

[tonyshouse]

The danger  is that you won’t be able to fix it if there is air infiltration after you move in