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Old 06-22-2010, 09:17 AM   #16
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cutting 4" holes in 10" floor joist


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Originally Posted by Michael Thomas View Post
Give Metwood a call, if allowed by your local AHJ, they may have a engineered joist reinforcement product which will solve your problem.
May the AHJ, at its discretion, forbid the HO to use this? If so, is the AHJ compelled to say why?

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Old 06-22-2010, 11:10 AM   #17
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cutting 4" holes in 10" floor joist


You can still comply with code by having a fix engineered. If an engineer signs off on the fix (such as metwood or any other reinforcing) I don't know why an AHJ would not approve it. BTW, don't cut the holes first and then start looking for a fix.
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Old 06-22-2010, 12:42 PM   #18
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cutting 4" holes in 10" floor joist


You are on the very edge of the limits here, and the big holes go in the center of the span where you loads on the joists are purely across the top and bottom edge. Also, you would need closer to a 10" actual board depth to get that 3.5" hole you desire.

Thinking creatively, since that's what us DIY schmucks do all too well, consider a couple other options:

1. Instead of PVC, ABS, or cast iron, look at copper tube instead. Yes, it will be pricey, but with a smaller outside diameter it might be the best solution to your problem, in that you might be able to bore smaller holes that will be within the specs of your floor system. Remember though, sewer pipe needs to drop 1/4" every 12" (I think), make sure you are not violating your minimums of top and bottom clearance for that slope through your joists.

2. Instead of cutting holes, cut the joists entirely... and put new load bearing beams across the sides of the new space you are making for your sewer pipe. You would have to take the load path all the way down to the foundation, but that is pretty straightforward, and you would retrofit joist hangers onto those new rim beams to hold the existing joists.
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Old 06-22-2010, 03:10 PM   #19
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cutting 4" holes in 10" floor joist


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Originally Posted by xxPaulCPxx View Post
Thinking creatively, since that's what us DIY schmucks do all too well, consider a couple other options:
..............................

2. Instead of cutting holes, cut the joists entirely... and put new load bearing beams across the sides of the new space you are making for your sewer pipe. You would have to take the load path all the way down to the foundation, but that is pretty straightforward, and you would retrofit joist hangers onto those new rim beams to hold the existing joists.
fwiw I used a similar approach re: PaulCP on point # 2 - cut them and add structure to existing to support the new space.

when I bought my house I retrofitted the bathroom and I had similar issue (to move the toilet). I didn't care about running pipe under the joists in my crappy old basement but I didn't want to mess with the connection to existing cast iron stack, etc. so the joists were in the way.

I followed the CMHC wood frame house construction book (i love this book) which details these things in a way even a DIY like me can follow. this was the gist of it in my case - not sure if this was overkill or standard procedure, but it sure worked well here. I hope this makes sense - great diagram in the book but i failed on a quick google around to find similar to link here.

-- cut about 12" right out of the offending joists - 3 of them in my case - enough room for flange, pipe, headers, etc
-- cut 2 headers to fit between the existing "trimmer" joists (those on each side of and parallel to the ones just cut) - nail these onto the ends of the hanging (tail) joists - one on each side of the opening
-- double up these headers (nail another header piece same size right over the first)
-- nail thru the sides of the existing "trimmer" joists into the ends of the new double headers
-- nail on an additional trimmer joist (same size - i.e. sister it against the existing trimmer joist to double it up)
-- add single / double joist hangers on the ends of the tail / header joist pieces

all materials and joists 2x8 in my case.

The CMHC book describes this as a basic framing technique for floor openings for stairs, etc. - in my case the "opening" was a just space under the subfloor - wide enough to accommodate the flange and the short pipe run across to the old stack. They do recommend getting an engineered solution for a "large" openings but this job was well within the guidelines they used. They also had some threshold where the "doubling up" might not be required, but a bit of overkill in this case was pretty easy to do regardless so I just did it.

The load carries across to wall / beam via the doubled-up trimmer joists - so nothing new underneath or at stack was required to support the change.

it took me a couple hours to complete and floor is now better than how I found it (previous owners had cut part way thru one joist and left it like that - not sure why - old houses full of surprises)

on the other hand, if you have hvac or electrical to contend with that might get in the way (e.g. running through the existing joists that you want to sister) this might not be of much value. others may also see problems with this in your case or in general - just throwing it out there fwiw. good luck...

Last edited by rtoni; 06-22-2010 at 03:17 PM. Reason: on second thought....
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Old 06-22-2010, 04:25 PM   #20
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cutting 4" holes in 10" floor joist


That's the way to do it ,as xxpaul and itoni says. Besides you couldn't fish a 4 foot pipe if you had a eight inch hole in all the joist. Get a grip!

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