Advice re bridging cavity to bi-fold doors

[Animal]

Hi all, I'm currently at the point of an extension being completed which has entailed 3 metre bi-fold doors being fitted. They are already fixed on the outer leaf (ie flush) on DPM so doesn't provide me with an option of using a cavity closer. The flooring up to the inner leaf is lined with visqueen, concrete, celotex and screed, however, there is a cavity gap which needs to be bridged as I wish to lay engineered wood flooring (this will run parallel to the doors). 

My builders take the **** out of me as they say I spend too much time Googling but all I want is to ensure things are completed correctly and mitigate the risk of damp transfer! One of the builders has suggested using wood noggins but feel inevitably this would fail over time.

 

I was looking into two possible solutions but wanted to seek someone's expert views;

 

The first possible solution is to use a combination of celotex and compacfoam but obviously needs to be sufficiently strong enough to support the weight of a person stood on the flooring. 

 

The second and my preferred option is to place visqueen in the cavity creating a sort of bathtub which will be filled with concrete, however, im not sure if I risk damp issues using this option. 

Can someone provide the correct advice in resolving this. I want to ensure there is no risk of damp tracking across the threshold or of course flooring giving way!

I have provided a library image which is almost identical to my situation.

Thanks in anticipation.

Edited November 7, 2021 by Animal
Grammatical

[ETC]

There should be insulation and an L-shaped DPC below and up the back of the cill the frame is sitting on. 

[Animal]

1 hour ago, ETC said:

There should be insulation and an L-shaped DPC below and up the back of the cill the frame is sitting on. 

Thanks ETC, yes I understand they haven't been fitted completely correctly and that's the point of my post! Are you referring to this?

[Animal]

I've just thought of a third option; fix heavy duty plates recessed into the inner leaf across the span which should spread the load across the flooring. This would be the least intrusive option in my opinion and a relatively easy albeit unconventional fix.

 

If anyone could help soonest it would really be appreciated as the flooring is due to arrive this week. ?

[Mr Punter]

Get rid of the inner leaf where the door opening is or take it down level with the slab, then run the DPM and foam all the way to the outer leaf.

[Animal]

18 minutes ago, Mr Punter said:

Get rid of the inner leaf where the door opening is or take it down level with the slab, then run the DPM and foam all the way to the outer leaf.

Thanks for your reply. I think I understand what you are saying but won't this still leave a void?

Edited November 7, 2021 by Animal

[Mr Punter]

Just take the inner leaf down level with the slab and fill the cavity with concrete level with the top of the slab.

 

[Animal]

1 hour ago, Mr Punter said:

Just take the inner leaf down level with the slab and fill the cavity with concrete level with the top of the slab.

 

 

Thanks again for this. Are you suggesting concrete (or screed) is added on top of the additional foam?  I don't want to appear ungrateful or dismissive, but can't I just put foam on the footing of the cavity without having to break down the inner leaf then put screed on top. I'm just trying understand why it is necessary and what issues may result.

[Mr Punter]

1 hour ago, Animal said:

 

Thanks again for this. Are you suggesting concrete (or screed) is added on top of the additional foam?  I don't want to appear ungrateful or dismissive, but can't I just put foam on the footing of the cavity without having to break down the inner leaf then put screed on top. I'm just trying understand why it is necessary and what issues may result.

 

Just extend the slab to the external leaf.

 

If you were to do as you originally suggested the screed over the cavity will only be supported by a thin bit of foam over a void.  You do not need a cavity in this section.