How can i Support structural floor on damp outside wall

[John D v2.0]

Hello everyone, I'd appreciate everyone's expertise here please!
I have a rear screen where the window is hanging at the outside of the wall, the wall is about 35cm thick (cavity filled with concrete, 25mm eps then render) see the photo below.
The rear screen has been fixed on brackets all round. At the bottom there's no damp proof course so the wall is damp in places.
My problem is the builders just cantilevered the internal plywood floor over the concrete so it was very bouncy at the edge. When I complained they just screwed diagonally into the window frames to stabilise it.
I need to make something proper to support things in the small available space, ideally without enclosing any timber that's going to rot.
Any ideas or suggestions I'm very grateful for.

 

[tomfe]

Your windows should be sat on a dpm, this could be extended up to the insulation then lay some foam and timber ontop of the dpm to support the ply floor.

 

[John D v2.0]

Thanks very much Tom, unfortunatelythe ship has sailed on the windows DPM, but I'll slot one in the rest of the width.
When you say foam and timber wedges, do you mean use folding wedges and use pu foam glue to stick them in place?

 

[tomfe]

Sorry wedges was the wrong word, just dpm and something to bring it up to the correct level, packers that's the word I am after.

Nice windows btw.

 

[John D v2.0]

Hi Tom thanks again, so I'll just cut some treated timber to correct lengths spaced as the joists, tie them all together with a long strip of ply? to stop them wandering and then fix the floor to that. Should I strap the ply/packets to the joists you can see on the left as well, just to keep it all in place while I'm screwing down the ply floor?

Can I fill the space with wool or similar, or is it best to let the air circulate somewhat?

 

[John D v2.0]

Ps thanks about the windows, they're Velfac, we had them in a flat we rented and they were great for sound proofing so we went for the same in triple glazed for here due to the A road outside.
The screen you see is 4 panels total 4.8m by 2.4m, one panel slides and one is a normal swing door, the others are fixed, as we were recommended against bi folds due to budget and the mechanism doesn't last as long as sliders apparently.

 

[chappers]

I would build some sort of framework off of the existing joists and maybe notch it under the window frames slightly and wedge it down tight to the floor so it doesn't bounce. as to the damp issues you really need to address that, but as you say you are where your're at now.
I would definitely lay some DPM in there first lapped up to the insulation, the foam under the windows should help protect the bottoms of the frames. I would cut the foam off at an angle to undercut the windows slightly, so you can tuck the membrane under slightly then build your frame. you could always foam in again once complete

 

[John D v2.0]

I would build some sort of framework off of the existing joists and maybe notch it under the window frames slightly and wedge it down tight to the floor so it doesn't bounce. as to the damp issues you really need to address that, but as you say you are where your're at now.
I would definitely lay some DPM in there first lapped up to the insulation, the foam under the windows should help protect the bottoms of the frames. I would cut the foam off at an angle to undercut the windows slightly, so you can tuck the membrane under slightly then build your frame. you could always foam in again once complete

Thanks chappers, I haven't started yet but given the depth available the framework will be thin. I'll dig out the foam completely to make space for the dpc.
Would you recommend chipping out the concrete at all to make more space for the framework?

 

[chappers]

that might be an option if you could get back to solid brick/block under the windows, you could then use the framework in place of the packers they have used under the windows if they are sat on solid brickwork.
Perspective makes it quite hard to see how much depth you have there but I wouldn't worry about how thick your supports are providing they are themselves supported sufficiently enough.
How far up the frames does the bottom of the ply come, and what distance are we taking from the timber subfloor to the windows, could you screw something to the window frames. maybe strips of ply with the concrete taking the weight

 

[John D v2.0]

Thanks chappers, I'm not sure I can do anything with the packers themselves as the windows are over 100kgs each due to 3 panes of glass around 3m² each.
The frames are 70mm tall timber sections at the bottom with around 30mm below the bottom surface of the plywood floor. Below the packers is about 40mm concrete sitting on 1 blockwork course filled with concrete, and that's directly on the foundation. I could trim back the inner leaf part of the equation, but it sounds like I wouldn't be helping really. The timber sub floor that's already there is around 300mm from the window frames at the moment.

So in summary I'd be best digging out the foam, dpc fitted in around the packers/fixings, then a framework of 2 by 2 cut to height all held in place by a strip of plywood screwed either to the window frames or the main floor.
And I'll pack round all that with wool/foam/celotex? to avoid thermal bridging. But if I do that I'm worried about leaving a humid unventilated void with timbers inside.

 

[John D v2.0]

If I get some time this afternoon I'll draw a section with rough dimensions as a picture will tell a thousand words without being as confusing to understand!

 

[chappers]

I would do your thing with the dpm, then cut some strips of ply that sit on edge on the concrete and screw them into the window frames at the relevant height so that your ply flooring will rest on them, it won't need any further support assuming it is 18mm, the 300mm span will be less than the span between joists on the main floor. If you do a decent job with the DPM you should eliminate any moisture in that void, I would fill it with wool

 

[John D v2.0]

Brilliant, makes perfect sense, I'll have a go as soon as I get time, thanks a million. John

 

[chappers]

most welcome