can any one tell me how much i can safely notch out of a 8 inch joist, i have always worked on the 33% rule...
notching joists.
- Thread starter rob1976
- Start date
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Do you need to notch the joist? Can't you drill a hole in the centre instead?
The guidelines (as an electrician) are that the notch should be no more than 1/8th of the joist depth and the notch should only be cut between 7% and 25% of the joist length from both ends.
So an 8 inch joist can only have a 1inch deep notch and if it is 5 metres long between supports then the notch can only be cut 35cm-125cm in from both ends.
The guidelines (as an electrician) are that the notch should be no more than 1/8th of the joist depth and the notch should only be cut between 7% and 25% of the joist length from both ends.
So an 8 inch joist can only have a 1inch deep notch and if it is 5 metres long between supports then the notch can only be cut 35cm-125cm in from both ends.
rob1976 said:
definitely not heard of this rule!
i concur with davy.
Depends on where you're notching it. If you're doing it near the bearing (and it's not already notched) you might be able to go quite deep - but it'd need to be checked. If you're doing it at the midpoint, you shouldn't be doing anything!
In steelwork there's a requirement to keep a connection within 60% of the depth of the beam, and I think there's something similar in the timber code (could be where your 1/3 is from). If that's the case, it's definitely only at the ends i.e. maximum notch at the ends to suit bearing connections.
I've seen too many jobs where we've been called in to sort out a big mess caused by an electrician or plumber hacking away floor joists. I like the sound of Davy's rule - it sounds perfectly reasonable - if only everyone followed it
In steelwork there's a requirement to keep a connection within 60% of the depth of the beam, and I think there's something similar in the timber code (could be where your 1/3 is from). If that's the case, it's definitely only at the ends i.e. maximum notch at the ends to suit bearing connections.
I've seen too many jobs where we've been called in to sort out a big mess caused by an electrician or plumber hacking away floor joists. I like the sound of Davy's rule - it sounds perfectly reasonable - if only everyone followed it
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This may be helpful:-
http://www.eastdevon.gov.uk/txt/bc-guidancenote7-notchingofjoists.pdf
http://www.eastdevon.gov.uk/txt/bc-guidancenote7-notchingofjoists.pdf
I think the 1/3 rule referred to is the middle third rule. This doesn't relate to notches but to holes that must be in the mid-third of the depth of the beam or joist. In any beam supported at both ends there are compressive forces in the top edge and tensile forces in the bottom edge. These cancel each other out at mid-depth. So we can drill a hole at mid-depth without reducing a beam's strength.
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