Tony Halmarack wrote in message . ..
snip

Tony,

Thanks for the reply, yes we have no underfloor access, I should of
course have pointed out that the rising main is under the window that
we intend to chop out to make an entrance to the proposed extension.

I'm going to try and contact the builders to ascertain the nature of
the suspended floor. Some of them I think use concrete beams that are
infilled with blocks. In that case I shouldn't need to worry about the
hole, as long as I drill through a block and not a beam )

My initial thought was that the floor itself was made from
pre-stressed slabs, a bit like lintels. Drilling a wide hole in one of
those would presumably relieve the "stress" and thus allow the whole
"lintel" to fold.

I'll let you know what I find out from the builders.

cheers
Mitch