Flat Warm Roof, Steel Beams and Cold Bridge

[BallyT]

Hi all - first time poster here and hoping I can get some help. My house is currently under construction, I have no building experience whatsoever but I'm now starting to think we have some issues.

We have a single storey, with a warm flat roof that adjoins a two storey block which is supported by 2 steel beams - 1 for the outer leaf and 1 for the inner leaf and concrete slab between ground floor and first floor. I've roughly drawn what I believe our detail to be below. 

Since we poured the screed flooring about 6 weeks ago we have had water pooling under the airtightness membrane near the steel. Obviously this is caused by condensation. My engineer is saying this will subside once the floor fully dries out. 

 

I have 2 concerns:

 

1. I'm pretty sure with the way it's built we will always have a terrible cold bridge on the beam supporting the outer leaf? Is there anyway to remedy this at this stage to ensure we minimise the risk of condensation going forward?
2. Is the warm roof build up correct? From researching myself, I see there should be a vapour control layer inserted directly below the insulation. The engineer is telling me the airtightness membrane further down serves the same purpose - but I'm not so sure.

 

Any advice would be much appreciated. Particularly on the actions we can take now to make the best of a bad situation (if my concerns outlined above prove to be valid).

 

Thank you.

Edited January 2 by BallyT

[Russell griffiths]

I would want both those beams fully enclosed in insulation of some sort, then wrapped in the fireproof system you are using. 
it might be a case of some sort of blown in insulation now if you can’t get to the webs of them. 
 

if the flat roof isn’t finished then pull the insulation up and insulate first then re install insulation on the roof.

what is stopping the cold in the cavity getting into the void above the false ceiling. 
 

I hope the ceiling isn’t up yet. 

Edited January 2 by Russell griffiths

[BallyT]

Thanks Russell, that's helpful.

 

The flat roof is finished unfortunately, but the ceiling isn't in yet. 

 

So I'll do the following:

 

Spray insulation into the webs. This will also close up the cavity (is that enough to stop the cold?).

Box the beams off internally with PIR or Aerogel.

Finally, wrap the whole lot with fire proofing. 

[Russell griffiths]

Do you have a cavity tray installed 

there should be a tray above those steels to prevent water dripping down the cavity. 
 

if you can’t get get the beams encapsulated in closed cell foam that would be excellent in my opinion. 
 

but let’s see what others say. 

[Redbeard]

What did your plans say about the Warm Roof build-up and about insulation and fire-proofing of the steels? Got any pics so we get more 'context'?

[torre]

@Russell griffiths I was literally typing cavity tray when I saw your reply. @BallyT you should be able to see weep holes all along the lead flashing over your upstand. Is your upstand insulated? Presumably you've some firrings to add a reasonable slope to this flat roof as well