Inserting door into cavity wall - how to provide support?

[GavS]

Hello all - long time reader of the forum and many thanks for the information I frequently borrow.

Perhaps I could ask for some views on an issue that has come up for me?

I have bricked up an existing doorway and am creating a new door way a few feet away. Its a 1930's semi. The wall is cavity construction for the bottom 3 feet or so but then flares in to become a single brick solid.

The old door had a large concrete step built in at the bottom and the door sat on this. The new doorway, however, doe snot have this and is currently two skins of brick with an approximate 70mm cavity between - the door cannot happily sit on only one skin of the wall due to frame depth and position. What I think I need is a wide concrete cill (like the old step) which would span the cavity and create a base for the door frame. A suggestion has been made to create a form out of DPM to lap over both brick skins, with a tray or well into the cavity, filling this with concrete to create a cill on which to set the door frame.

Is this adequate and reasonably sensible or are there other options?

Thanks.

 

[noseall]

A door frame is secured to the masonry jambs and for the most part is supported by these. However in order to support the sill you can form a masonry or concrete support anyway you please as long as it does not create form a thermal bridge i.e. that you take steps to ensure a thermal break between the masonry of the sill and the internal floor etc. Would not a brick special be a better idea?

Sash windows use a similar principle in that they are located on the inner leaf and require a masonry sill construction that deals with the window set-back position. I'm sure there are design details which deal with this.