ProDave Posted May 31, 2016 Share Posted May 31, 2016 Whoever does come back, make sure they know what the correct rules are regarding drilling joists, but to make the No 1 objective to route cables and pipes to avoid drilling the joists if at all possible. Link to comment Share on other sites More sharing options...
Jeremy Harris Posted May 31, 2016 Share Posted May 31, 2016 That's good news, means there is plenty of reserve in the trusses. I'm still a bit amazed that the electrician didn't consider the implications of drilling holes like this. IIRC, there was a bit back when I did the 15th Ed ticket, 25 odd years ago, that related to the safe areas for cable holes, spacing of them etc. I can't believe that this has changed much since, and it has to be still within the current regs somewhere (I don't have the 17th Ed here on this machine, but will check later). Link to comment Share on other sites More sharing options...
Declan52 Posted May 31, 2016 Share Posted May 31, 2016 Might not have been a spark who done the drilling. An apprentice maybe could have got that nice job although he might have been only following marks left on the truss. Who knows. Link to comment Share on other sites More sharing options...
Shell820810 Posted May 31, 2016 Author Share Posted May 31, 2016 There was an experienced electrician and a younger Polish guy. Not sure who was responsible for it but it appears everyone but those two knew that you should not be drilling trusses to that extent. They were only there two days and had done that and set all the boxes with bonding which is also apparently a big no-no. These will have to be taken out and re-set. Not sure if they are taking shortcuts because they are being subcontracted in and don't care, or if that is the general quality of their work. The electrical contractor will be given the chance to put his own men on the job, or else I assume they will look for a new contractor. ETA: the only reason the joists remain viable was because they were 8" x 2" joists. If they had even been 7" by 1.5" it wouldn't have been as clear cut. Link to comment Share on other sites More sharing options...
tonyshouse Posted May 31, 2016 Share Posted May 31, 2016 What engineer has said that it is OK is this the one from the truss manufacturer or is it a general engineer (Get the letter fast) this is normal advice http://dwbgroup.co.uk/Limits_for_Cutting_Notching_and_Drilling_Of_Trussed_Rafters.pdf Link to comment Share on other sites More sharing options...
ProDave Posted May 31, 2016 Share Posted May 31, 2016 1 hour ago, tonyshouse said: What engineer has said that it is OK is this the one from the truss manufacturer or is it a general engineer (Get the letter fast) this is normal advice http://dwbgroup.co.uk/Limits_for_Cutting_Notching_and_Drilling_Of_Trussed_Rafters.pdf I don't think anyone has said this is "okay" as in general guidance. Only that in THIS case they have "got away" with it because they were over sized. P.S thanks for that link relating specifically to attic trusses. I have never seen that before and that will now ovveride the normal 0.25 to o.4 span rules. 1 Link to comment Share on other sites More sharing options...
tonyshouse Posted May 31, 2016 Share Posted May 31, 2016 There is a general point to make here and that is "trusses are not the same as joists" different rules apply. 1 Link to comment Share on other sites More sharing options...
Jeremy Harris Posted May 31, 2016 Share Posted May 31, 2016 41 minutes ago, tonyshouse said: There is a general point to make here and that is "trusses are not the same as joists" different rules apply. That's a very good point, as I'll bet that it isn't common knowledge that trusses have significantly higher stresses in the timbers, because they work as a composite frame, with loads distributed throughout the truss. Using joist rules of thumb for making holes in trusses is inherently deeply flawed, but it's easy to see how the lower member of a truss could be considered to be "just a ceiling joist" by some, when it's not at all in terms of the loads it is carrying. 1 Link to comment Share on other sites More sharing options...
Guest Alphonsox Posted May 31, 2016 Share Posted May 31, 2016 52 minutes ago, tonyshouse said: There is a general point to make here and that is "trusses are not the same as joists" different rules apply. For completeness what rules typically apply for drilling joists ? Link to comment Share on other sites More sharing options...
ProDave Posted May 31, 2016 Share Posted May 31, 2016 55 minutes ago, tonyshouse said: There is a general point to make here and that is "trusses are not the same as joists" different rules apply. +101 to that. The thing is, I heve never before this seen any specific guidance on drilling the bottom chord of an attic truss. All the normal electricians on site guides etc make no mention of a truss being any different. I suspect I and countless other electricians have just treated them as an ordinary "joist" and lacking any proper guidance have drilled them within the limits for a "joist" which we now know is not the case. P.S for ordinary joists you must only drill them in an area between 0.25 and 0.4 of the span, only along the centreline of the joist and no more than 0.25 times the depth of the joist. Link to comment Share on other sites More sharing options...
tonyshouse Posted May 31, 2016 Share Posted May 31, 2016 We always drilled joists 2/3 of the way up and never notched them. And holes only 1/8 joist depth .2 to .4 out. always drill square, we piled the joists on top of each other humps same way round and drilled through the lot before fitting them. http://www.diydoctor.org.uk/projects/Notching_joist.htm Link to comment Share on other sites More sharing options...
daiking Posted May 31, 2016 Share Posted May 31, 2016 8 hours ago, Shell820810 said: They were only there two days and had done that and set all the boxes with bonding which is also apparently a big no-no. Just out of curiosity, not personal worry, what's the reason for this? Link to comment Share on other sites More sharing options...
Nickfromwales Posted May 31, 2016 Share Posted May 31, 2016 The wet dab rots the box for one . Link to comment Share on other sites More sharing options...
daiking Posted May 31, 2016 Share Posted May 31, 2016 14 minutes ago, Nickfromwales said: The wet dab rots the box for one . I thought I'd seen it advocated before for airtightness in a block build where chasing is required for boxes. Link to comment Share on other sites More sharing options...
tonyshouse Posted June 1, 2016 Share Posted June 1, 2016 Yes, probably by me. In the old days used to standard practice, followed by a cut nail the next day! I like parge or bonding behind chased in boxes on outside walls, generally galvanised boxes don't rot in dry plaster (any more than angle beads do) and this improves air tightness for those with OCD Link to comment Share on other sites More sharing options...
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