Bridging cavity solution please

[Multibez]

So we are having a new set of bifold doors fitted to the rear of our circa 1925 house where an existing window was.

After the window has been removed and both inner and outer leaf are brought down to DPC level I am going to be left with a gap from the cavity from where my original floorboards butted upto inner leaf, ie floorboards run parallel with wall. So my Q is how do I cover this threshold from existing flooring to track of bi fold doors over inner leaf/cavity approx 2 floorboard widths without causing damp/thermal problems etc....

hope that makes sense

mark

 

[themiddleagedun]

The easiest way would be to knock of the top course of internal brick, and line the cavity with visqueen, and fill with concrete level to the top of your floorboards. I wouldn't worry about the thermal issue...

 

[Multibez]

Thanks for the reply but the void underneath is about 3 feet!!!

 

[John D v2.0]

have you any insulaton in the cavity?
We had the same issue on a new opening on a similar age house. I had a struggle due to missing DPC and no ventilation and little under floor space so I had to follow a different solution but similar to the below.
In your case I'd knock off the top rows of bricks, bed a wall plate onto a dpc there if possible without it getting damp, take up the floorboards adjacent to it, extend the joists slightly and rest on the new wall plate if it was possible, if not cantilever them by bolting together and replace the floorboards with a sheet of flooring plywood.

 

[JohnD]

can you see the dpc in the inner and outer leaves of the wall?

In the old days the cavity used to be filled only to dpc level, and finished with a slight slope to the outside in case of rain penetration.

I imagine your cavity is only a couple of inches wide so it wouldn't take many barrowloads.

Outside the UK I have also seen sub-grade cavities filled with Foamglas, which is damp-proof, but (currently) almost unobtainable here unless you order a lorryload.

You'll need to include plenty of ventilation, and it's vital to prevent damp reaching your joist ends, which I suppose are built into the inner leaf, or an additional dwarf wall.

 

[Multibez]

can you see the dpc in the inner and outer leaves of the wall?

In the old days the cavity used to be filled only to dpc level, and finished with a slight slope to the outside in case of rain penetration.

I imagine your cavity is only a couple of inches wide so it wouldn't take many barrowloads.

Outside the UK I have also seen sub-grade cavities filled with Foamglas, which is damp-proof, but (currently) almost unobtainable here unless you order a lorryload.

You'll need to include plenty of ventilation, and it's vital to prevent damp reaching your joist ends, which I suppose are built into the inner leaf, or an additional dwarf wall.

have you any insulaton in the cavity?
We had the same issue on a new opening on a similar age house. I had a struggle due to missing DPC and no ventilation and little under floor space so I had to follow a different solution but similar to the below.
In your case I'd knock off the top rows of bricks, bed a wall plate onto a dpc there if possible without it getting damp, take up the floorboards adjacent to it, extend the joists slightly and rest on the new wall plate if it was possible, if not cantilever them by bolting together and replace the floorboards with a sheet of flooring plywood.

cheers Guys,

There is no insulation at the moment, and we are looking to add some , the cavity is 50mm,

when you say "can i see the DPC" i can see the air bricks from the inside,

having done some more research, im thinking of running cavity closers all around the cavity perimeter, would that work