Closing cavity below door?

[dent]

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.

[Tim W]

dent wibbled on Tuesday 13 October 2009 12:19

If below the dpc, can you just fill it with a bit of concrete?

Otherwise, how about a metal plate screwed down across the top?

I have the same scenario - I'm going to fill mine with concrete as it's only a couple of courses deep.

[Jim]

There is a cold bridging issue here, of course - insulation should be carried right the way through and upturned inside the outer leaf of masonry.

[Tim W]

Jim wibbled on Tuesday 13 October 2009 12:40

That's true. I don't have any insulation in the floor so I'm not that bothered - but I guess one could put a 25mm vertical bit of celotex against one face before infilling. Or use a wood filler (with DPC between it and the outer leaf).