New 1st floor extension - improving air tightness help?

[rh2205]

Morning,

 

Probably a bit late in the day to be posting this but our architect didn’t really have much knowledge of the area & our builder just does things the old way (much more common in the refurb area than new build I know)!

 

The new roof & 1st floor is a warm roof formed of 100mm PIR between the rafters with 50mm air gap & roof membrane & then 50mm phenolic insulated plasterboard below rafters. For the walls it is 70mm PIR between the studs with membrane, then 70mm PIR externally with another membrane on top before the cladding. Outside walls & roof etc done but insulation still exposed on the inside/not finished as pretty big area for them to cut between. Anything we can do internally at weekends at this late stage to improve airtightness?

 

We have ended up going with a air source heat pump as no gas but are now concerned we should be doing more on airtightness as nothing else other than the description above put on the drawing so I presume it won’t be particularly air tight hoping others have some suggestions as really struggled with information on what we can do to reduce leaks?

 

FYI downstairs is a refurb with 90mm EWI & 50mm EPS cavity fill we are having velfac windows set out using lugs into the insulation but doors/patios are another leaky conundrum and have to be set on the bricks (not even in line with cavity due to some old steel lintels we hadn’t considered & render not being able to go over these). We know this is a cold bridge issue but window orders are done so cannot bring insulation into the reveals now & velfac sashes have no fixed frame it all moves so cannot overlap at all externally. Would some Xtherm 20mm insulated plasterboard on the door internal reveals make this situation any better or is this just throwing more money after bad? 

 

These are all things we requested to be added on insulation wise with architect but really we are not experienced in this & have just been trying to make sure we could get it built quickly given we are renting so our ideas may be somewhat of a halfway house.

 

Basically we think other than the downstairs door screw ups we had some kind of insulation plan just execution might now not be right as I get the impression from reading it’s actually the details that matter especially to stop air leaks?