How to finish off cavity and run floor up to new installed bifold

[Osman]

Good evening everyone,

 

I wonder if I can get some help/thoughts on how to finish the below:

 

I recently got a room renovated in my 1930s house, at the end of the room an extension was done sometimes in the 50s/60s, the extended part has a patio door which was recently replaced with a new bifold sitting on the outer leaf.

The workman put down new joists (suspended timber floor) and the joists was run resting on the inner leaf of the masonry as in picture.

Also, telescopic vents were installed under the bifold which crosses between outer and inner wall to help with subfloor ventilation.

 

I now have the cavity to finish, so I can run the floor (chipboards/plywood bords) going all the way up to the bifold door, the workmen suggested no need for cavity closer when they did the work. I am unsure how to finish off the cavity up to the bifold to avoid cold bridging and any damp. I am concerned the plywood/chipboard in that area will build up mould.

 

What is the best approach in this situation, all thoughts are much appreciated.

[Big Jimbo]

You could wedge a piece of pir across the cavity. Either 50 0r 100mm if you have room. Then your ply, then your wood flooring. That is providing that your new floor joist have all been extended over the cavity to support the ply.

[Redbeard]

1 hour ago, Big Jimbo said:

That is providing that your new floor joist have all been extended over the cavity to support the ply.

 

Ah, there's the rub. If I am seeing pic. 2 correctly then at least 1 joist (and how many more?) does not extend across the cavity. (a 'missed trick', perhaps,  as the OP says (I think) that it is a newly-laid floor). Looks as if some brickwork and floor will maybe have to be removed in order to be able to 'sister' a new oversailing piece of joist alongside.

 

Not knowing the nature of the sub-floor (is it moist, for example?) I would not risk suggesting some sort of load-bearing/insulating fill to that cavity.

[Iceverge]

Get some EPS200 and wedge/hammer it down until it hits something solid. Make sure you don't block any ventilation for the floor. 

 

Foam it in place with illbruck FM330.

 

Trim the top of the EPS flush with the top of the joists. 

 

Stick the plywood to the top of the EPS with stixall or CT1. 

 

Apply masking tape to the door and floor before you do this as the foam and sealant will be hard to clean off. 

[Redbeard]

13 minutes ago, Iceverge said:

Get some EPS200

 

I don't know EPS200, so I don't know for certain whether it wouldn't 'suck' at all in adverse conditions. XPS definitely doesn't, though, AFAIK.

[Osman]

3 hours ago, Iceverge said:

Get some EPS200 and wedge/hammer it down until it hits something solid. Make sure you don't block any ventilation for the floor. 

 

Foam it in place with illbruck FM330.

 

Trim the top of the EPS flush with the top of the joists. 

 

Stick the plywood to the top of the EPS with stixall or CT1. 

 

Apply masking tape to the door and floor before you do this as the foam and sealant will be hard to clean off. 

Thanks for all the steps here, very helpful, should a DPM be installed at any stage here to wrap the EPS? and would PIR also work as Big Jimbo suggested in his comments? 

[Osman]

6 hours ago, Big Jimbo said:

You could wedge a piece of pir across the cavity. Either 50 0r 100mm if you have room. Then your ply, then your wood flooring. That is providing that your new floor joist have all been extended over the cavity to support the ply.

Thanks, would I need to wrap the PIR in DPM or would the foil be enough?

[Iceverge]

3 hours ago, Redbeard said:

 

I don't know EPS200, so I don't know for certain whether it wouldn't 'suck' at all in adverse conditions. XPS definitely doesn't, though, AFAIK.

 

EPS can soak water but that's typically only when fully immersed and then worst case is only 5% or so.

 

The amount wicked up by capillary action from damp ground is typically negligible as the capillary network between the EPS beads is far larger than brick or soil. 

 

If you're concerned, a capillary break like a shovel of gravel below the EPS would certainly solve it. 

 

On the other hand if you have some XPS to hand that would work equally well in this situation if it has sufficient compressive strength.