Ceiling Joists - remedial work required??

bwbm

Hi all - this is my first time so go easy!

I am starting a house renovation, first element being a full re-wire. Having removed the old kitchen ceiling, it appears many of the ceiling joists have been weakened by previous electricians / plumbers cutting notches (for pipe work) and drilling holes (to thread wiring) – my electrician is concerned they have been overly weakened and is unwilling to start drilling more holes without my specific say so (or required remedial work undertaken to strengthen them).

Technical detail is: house is c. 100 years old. Joists are 5 by 3 inches. Worst case is a c. 1 inch deep notch has been cut in the top (for water pipes to pass under floorboards), with a 25mm hole drilled directly underneath (to thread wiring) thus reducing the solid joist depth at that point by approx. 40%.

These ‘plumber’s notches’ and ‘electrician’s holes’ (!) are all over but nowhere worse than worst case above. My wholly uneducated opinion is that it’s not ideal but - as it’s a low traffic bedroom above and any load is shared over the joists via the floor boards – expensive remedial / strengthening / replacement work is not necessary… but very happy to be advised otherwise by people less ignorant than myself…

Apologies for the long post and thanks in advance for your advice…

Doozergirl

Are you getting any 'bounce' upstairs?

bwbm

Not that I recall (though will assess this evening). The floor of the bedroom above definitely has a slope along the length of the joists (internal wall to external) though this is unrelated to the 'weakening' described in original post - though I am considering laying a new floor on top of the existing one to level it (though much further down the renovation line)...

jaywhoopee

The answer will depend on the spacing of the joists and the span they cross unsupported. There's a table in building regulations but an abridged version is here: http://www.diydoctor.org.uk/projects/load-bearing_walls.htm

I'm not an expert but my understanding is that notches top or bottom could weaken a joist more than a hole in the middle (the load on the top of the joist translates into the top of the joist being in compression along the length of joist and the bottom being in tension, while the middle is somewhat more neutral).

Could the sparky not use existing holes to at least not worsen the situation?

Beware of adding extra weight (leveling the floor above) without adding strength and if in doubt consult a builder or structural engineer.

googler

Google a technique called 'sistering' - basically bolt on engineered lumber each side.

iamcornholio

Don't worry too much about excessive notches ....



LOL

If you are worried, you can strengthen joists over notches by bolting another section of timber to one side, or possibly easier and better, glue and nail some plyboard each side of the joist