"Andrew Mawson" wrote in message
...

"AndyM" wrote in message
...
Hello all,

I need to replace a 22mm pipe under the kitchen floor. The original
one, it
appears, was put in when the house was built as there is no way I
can get a
length under the joists.

The joists are 4" x 2" resting on brick supports. The routing would
take the
pipe parallel to and 12" from the support.

Q. Can I cut a U shaped notch 22mm deep in the top of each 4"
joist, 12" from
the support, without seriously weakening the joist?

Thanks

AndyM

Can't answer your queston without delving into the beam equations, but the
highest stressed parts of a joist are the top andthe bottom: something
called the 'neutral line' runs through the centre, which suffers neither
tension nor compression, only the shear (45 degree) forces that beams have.
Thus, it is true to say I think, that the least weakening of the beam will
occur if the hole goes through the middle of the beam.

Andy.