Hi all

I am currently renovating a back room at one end of which there is a bar (as
in for serving drinks).
Above the bar area is a lowered "ceiling" section, basically timber frame
with wood cladding.
An extension was built by the previous owner above this bar with an en-suite
and associated plumbing.
Removing the box cladding below shows that the plumbing has been carried out
in plastic pipe which hangs below joist level into the space above the
boxwork.


So, to allow for a level ceiling throughout the downstairs room, can I notch
the underside of the joists for 15mm plastic pipes or will this introduce
serious weakness?

The joists seem quite substantial (can't remember dimensions off hand) and
span about 3m.
Are there rules about notching underside of joists? I've seen rules for
cutouts in tops of joists eg position and depth as a percentage of overall
joist depth.
I would consider putting metal straps across the notches to avoid any
plasterboard nails hitting the pipes.

TIA

Phil

TheScullster phil-at-dropthespam.com wrote:
Hi all

I am currently renovating a back room at one end of which there is a bar (as
in for serving drinks).
Above the bar area is a lowered "ceiling" section, basically timber frame
with wood cladding.
An extension was built by the previous owner above this bar with an en-suite
and associated plumbing.
Removing the box cladding below shows that the plumbing has been carried out
in plastic pipe which hangs below joist level into the space above the
boxwork.


So, to allow for a level ceiling throughout the downstairs room, can I notch
the underside of the joists for 15mm plastic pipes or will this introduce
serious weakness?

The joists seem quite substantial (can't remember dimensions off hand) and
span about 3m.
Are there rules about notching underside of joists? I've seen rules for
cutouts in tops of joists eg position and depth as a percentage of overall
joist depth.
I would consider putting metal straps across the notches to avoid any
plasterboard nails hitting the pipes.

Undersides is worse.
Is it possible to do a hole through the middle of the joist, and
thread the pipe through it?

Ian Stirling wrote:


Undersides is worse.

I'd think so - the load's from on top, the deflection puts the top in
compression and the bottom in tension. A "notch" will open up more
readily if the side it's on is being stretched rather than squashed, I'd
guess; certainly, the round-portholes arguments (sharp corners = stress
concentration = crack propagation) say that if you *do* notch, you're a
*lot* better off drilling a 15mm hole and cutting down to its sides,
than just making two cuts and chiselling out the waste.

Is it possible to do a hole through the middle of the joist, and
thread the pipe through it?

That'd be better - the phrase "neutral axis" leaps to mind (since the
top's in compression, the bottom's in tension, stands to reason that a
band in the middle is under not-much stress). Sparkies get told to drill
through in preference to notching (but much more to avoid cables running
within typical-nail-length distance than for structural reasons), to
limit notches to 1/8th the joist depth and make them within 0.1 and 0.25
of the span (i.e. close to, but not at, the ends), while holes shoudl be
on the centre line, no more than 1/4 the joist depth, and towards but
not at the middle (between 0.25 and 0.4 of the span), and no hole within
3 diameters distance of another: hopefully those guidelines are relevant
to this situation too...

HTH - Stefek

Is it possible to do a hole through the middle of the joist, and
thread the pipe through it?

If you do so, and it is the correct way to proceed, then use plastic
pipework (unless gas!), as it is far easier to thread through than rigid
metal and doesn't require accurate hole positioning, or multiple joins.

Christian.