"marvin" wrote in message
...
I'm putting an 12ft RSJ in, one end into a cavity wall.

What sort of cavity wall. RSJs require strong mounts.


When I have opened the wall there is the end of a wood lintel that is
supporting the inside wall over a window.
If i cut the wood so that the RSJ sits on brick that would only l;eave about
3-4 inches of the wood left sitting on brick.

Not allowed. Must be 6 inches minimum.


Alternatively can I sit the RSJ on the wood beam (with the packing
slate in between), but even then I would have to take some of the wood
off for it to fit.?

Probably not. Your Building Control Officer has final say so see what he
wants.

Few queries here.
1) How thick is the wall?
2) What will be the loading of the RSJ?
3) What does the lintel support?
4) What is the span, and size of the lintel?

I'd be rather concerned at supporting an RSJ on a single brick wall without
a pillar and a concrete load spreading pad. Maybe the answer to the lintel
support problem is to replace the lintel with a piece of angle iron, which
would enable the rsj to be fitted above it.
Regards
Capitol