dundonald wrote:
Pete C thoughtfully wrote:

On Fri, 23 Apr 2004 00:54:35 GMT, Ian Stirling
wrote:

dundonald wrote:
the top of the joist.
snip

Anyone hazard a guess as to how much a diagonal 5*7.5mm slot in a
50x75 joist would reduce it's strength?

I thought of this, and wondered if to post it.

Is this much different than a 'notch' in the joist?

Maybe.
The notch is now in some ways equivalent to the average cut-out depth across
the beam.
If the above notch was 5mm in depth, then that would sort-of convert the
5mm notch into a .5mm notch.

Take a thin bit of wood, perhaps a lolipop stick.
Cut halfway through with a knife.
Now, do the same at a sharp angle.
Compare strengths.

I would still cut out the slot in the chipboard, rather than the joist.
A circular saw, set to 5mm depth can be used for this.