Browse Forums Building A New House 1 Dec 16, 2019 9:59 pm Hi all. Noticed these large holes in floor joists for air con ducting. Cut out is almost the complete height of the joist so there's not much left holding up the floor. Is this normal? I'm guessing/hoping they'll attach some steel reinforcing around the cut outs at some stage? Thanks. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ Re: Floor joist holes for ducting - normal? 2Dec 16, 2019 10:02 pm That's normal, they are engineered that way, no dramas at all. Re: Floor joist holes for ducting - normal? 4Dec 17, 2019 9:37 am Joker Always thought holes couldn't be more than1/4,1/3 of joist,to he sure keep asking , plenty of forum experts can answer . https://www.tilling.com.au/product/smartjoist/ Re: Floor joist holes for ducting - normal? 5Dec 17, 2019 9:45 am Joker Always thought holes couldn't be more than1/4,1/3 of joist,to he sure keep asking , plenty of forum experts can answer . Yeah seems like it would be severely weakened - particular as its about a 4 meter span and the whole lot of the joists in that area have the hole in same spot. I wonder what's holding the floor up if the joists have been basically cut in half in the middle. Re: Floor joist holes for ducting - normal? 6Dec 17, 2019 3:16 pm supersleuth Hi all. Noticed these large holes in floor joists for air con ducting. Cut out is almost the complete height of the joist so there's not much left holding up the floor. Is this normal? I'm guessing/hoping they'll attach some steel reinforcing around the cut outs at some stage? Thanks. Like ⋅ Add a comment ⋅ Pin to Ideaboard ⋅ In the centre of the I joist they are engineered and perfectly fine. They cant be close to the ends. I have the codes and formulas from the manufacturer so if you would like me to email them to you PM me Simeon McGovern Affordable Custom Homes, We design and build to your budget Ashington Homes www.ashingtonhomes.com.au Re: Floor joist holes for ducting - normal? 7Dec 17, 2019 3:29 pm supersleuth Joker Always thought holes couldn't be more than1/4,1/3 of joist,to he sure keep asking , plenty of forum experts can answer . Yeah seems like it would be severely weakened - particular as its about a 4 meter span and the whole lot of the joists in that area have the hole in same spot. I wonder what's holding the floor up if the joists have been basically cut in half in the middle. Volume builders all uses hyjoist. As oppose to posi strut or pyrda joists. While custom builders all uses these. Don't think they r much more expensive just that volume builders build so mnay house if each house save $1000. I guess it all adds up. Re: Floor joist holes for ducting - normal? 8Dec 17, 2019 6:21 pm Hi supersleuth The general rule of thumb is that penetration sizes should be less than 2/3rd the depth ie 300mm x 2/3 = 200mm imo that will need to be stiffened If you don't have a copy of your certified structural floor joist engineering Plans & Details I suggest you get a copy and look under notes for other requirements. Cheers Chris Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Floor joist holes for ducting - normal? 9Dec 17, 2019 6:47 pm according to page 22 seems ok depending on sizes http://www.belmonttimber.com.au/Guidlines/Wesbeam_joist_installation.pdf Re: Floor joist holes for ducting - normal? 10Dec 17, 2019 7:14 pm Those holes are CNC cut so they have obviously come from the factory like that and one would assume as Doozer1905 said they have been engineered as such. Accessible Carpentry & Cabinets accessiblecarpentry@gmail.com accessiblecarpentry.com.au https://www.facebook.com/pages/Accessible-Carpentry-Cabinets/583314911709039 Re: Floor joist holes for ducting - normal? 11Dec 17, 2019 7:32 pm chippy Those holes are CNC cut so they have obviously come from the factory like that and one would assume as Doozer1905 said they have been engineered as such. Re: Floor joist holes for ducting - normal? 12Dec 17, 2019 10:12 pm aussieta according to page 22 seems ok depending on sizes http://www.belmonttimber.com.au/Guidlines/Wesbeam_joist_installation.pdf Thanks yep that seems to clearly show a large cut out 5mm from the flange so I guess all good. Still boggles me how this doesn't significantly weaken the joist. Maybe for the distance across the hole the flanges are thick enough to stop it shearing, and the distance is too small for it to bend. Re: Floor joist holes for ducting - normal? 13Dec 17, 2019 10:17 pm chippy Those holes are CNC cut so they have obviously come from the factory like that and one would assume as Doozer1905 said they have been engineered as such. Hey mate. Yeah at first I was thinking they must have had a template and special router tool to cut them so neat, but what you say about coming from the factory like that makes more sense. Re: Floor joist holes for ducting - normal? 14Dec 18, 2019 6:44 am supersleuth Still boggles me how this doesn't significantly weaken the joist. Maybe for the distance across the hole the flanges are thick enough to stop it shearing, and the distance is too small for it to bend. You can't tell from your photo what load is on top of the I joist If there is a wall or significant load above, it requires stiffening and you aren't expected to know that.. even more reason to have the engineering drawings and ask questions hth Designer,Engineer (Civil,Const & Envir),Builder,Concrete & Masonry Contract.Struct Repairs Re: Floor joist holes for ducting - normal? 15Dec 18, 2019 8:45 am Can I say this type of joist used by 99.9% of volume builders and there are tens of thousands of houses in the last 20 years at least. We have read of many new houses which have various issues none related to floor joist failure. And mind u. I reckon minority of contactors would also simply cut when they do their plumbing and electrical rough ons. I think OP should concentrate on other parts of the house. Since his joists are so nicely cut at factory. Assuming you've modelled the TB8, TB10, TB12, TB2 & J1 joists/LVLs there, it appears as per drawing to me. There maybe should be an additional J1 between TB10 and T12 if… 3 31816 1 10131 Seconded; we just used these last weekend to build a small deck. They worked perfectly as we have bluestone in the area where we wanted to build so digging down was not… 8 9063 |