Hi all,

I am building a small extension, but I'm not sure about how to close
the cavity below the door. It's a 300mm wall (100 block leaves,100
cavity). The door is 700mm off the ground, with a flight of steps and
a landing leading up to it. Inside there will be a suspended floor,
covered with narrow oak T&G boards running parallel to the door. The
door will sit within the outer leaf of the cavity wall, so there will
be support directly below the door for the threshold, but how should I
support the floor across the cavity? I will be using cavity closers
for the side and top, but these are only uPVC and not sturdy enough to
support the floor. If the floor boards ran perpendicular to the door,
then the ends could bridge the cavity cantilever-style, but this won't
work with the boards running parallel.

Is it possible to buy cavity closers which are strong enough for the
job? I can't find any online, but maybe I'm using the wrong search
terms.

I did wonder about leaving a row of blocks out below the door, and
then extending the floor joists (perpendicular to the door) into and
almost across the cavity, to provide the necessary support, and then
lowering the DPC around the bottom of these across the width of the
door.

Any suggestions gratefully received.

thanks,

dan.