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Thread: Question About Running Pex

  1. #1
    DIY Junior Member philwgreen's Avatar
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    Default Pex and Engineered Joists

    Getting ready to run my supply lines on a new addition. I'm using the Uponor pex and fittings and I had a question about running them in the joist bay.

    I've attached a picture below showing roughly where one of the runs will go. I'm branching off my 3/4" main supply for hot and cold...I have one bathroom on a second floor and a utility sink in the first floor garage. A typical run will have the 1/2" line run parallel to the joist for about 5' from the far wall to where it's teed from the 3/4" line.

    My first thought was it would be easier to run my 1/2" lines down the middle of the joist bay - to get me in the right spot for the lav - but I don't know how to support the line in the middle of the joist bay. If I run the 1/2" along the joist itself how would I insulate the line when it's up against the joist? Also, with these being engineered i joists - I'm not sure how to properly fasten the PEX to the joist. I can't seem to find any info on the manufacture's website.

    Or am I missing something obvious and is there an easier way to run that line? Just curious how everyone else handles running lines parallel to engineered joists.

    Name:  joist_bay.jpg
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    Last edited by philwgreen; 07-30-2013 at 02:53 PM.

  2. #2
    Moderator & Master Plumber hj's Avatar
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    What kind of insulation and how thick? You need "straps" which will fit over it nailed or screwed on to the web.
    Licensed residential and commercial plumber

  3. #3
    DIY Junior Member philwgreen's Avatar
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    I was assuming I had to put the foam insulation sleeves around the pex, but I'm not sure how thick that is.

    The bottom side of the floor will be sprayed with foam insulation - but only 5" thick so the pex will more than likely be exposed.

    I just wanted to make sure the straps could be screwed/nailed into the web. I wasn't sure after reading the manufacturer's instructions.

    It seems like the best way would be to secure to the joists, correct? That way I can secure every 4' - I wasn't sure how to do it otherwise.

    Another random question. When I add a tee from the 3/4" line how can I keep that fitting tight up against the hole in the joist? Do I just drill a hole in the joist big enough for the uponor ring to also fit through?

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    Forum Admin, Expert Plumber Terry's Avatar
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    It looks to me that you have a non vented p-trap in the flooring. What does that serve?

    PEX can be installed in bundles. That means you can drill a larger hole and put both the hot and cold together.
    My normal drill bit size for water supply is 1-3/8"; unless I'm combining.
    I sometimes use some closed cell foam and then plumbers strap to hold it.

  5. #5
    DIY Junior Member philwgreen's Avatar
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    Quote Originally Posted by Terry View Post
    It looks to me that you have a non vented p-trap in the flooring. What does that serve?
    That p-trap is for a shower. It's kinda hard to see the vent but it's there. It's to the right of the trap - in the next joist bay over. You can just barely see the pipe in that bay.

    Did another quick drawing just to sketch out an example hot supply line. Looks like from what I've read here I am ok to strap the pipe to the web of the I joist.

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  6. #6
    Plumbing Contractor for 49 years johnjh2o1's Avatar
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    As far as the shower vent it can't run horizontal unless it's 6" above the flood rim of the fixture.
    John

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    In the Trades Tom Sawyer's Avatar
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    The second floor bath will need separate hot and cold feeds, with shutoff s in the basement. In other words, you need to isolate 2nd floor piping from 1st floor.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  8. #8
    DIY Junior Member philwgreen's Avatar
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    Tom, yes I will have hot and cold with shutoffs - I just didn't draw them in the sketch.

    As far as the shower vent goes, it looks like it's wrong. I actually had a 'master' plumber do the DWV system and I wish I would have checked with the forum beforehand. Luckily, it's not too late to correct anything. My question is: since the shower is a center drain, how do I avoid a horizontal run on the shower vent? Attaching a new picture to show how it's currently run.

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  9. #9
    Nuclear Engineer nukeman's Avatar
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    Typically, the best way to handle the shower is with a wet vent. If that vent was actually the drain for the lav and if it was 2" pipe, then it would be okay. It looks like it reduces to perhaps 1.5" before going up, so my guess it is a dry vent. Since it is flat before 6" above the flood rim, it is not allowed.

    The other common option is to run the trap to the nearest wall (without connecting to anything else) and then take a vertical vent off at that wall. For 2" pipe, you can run between 5' and 8' (depending on code) before you have to vent.

  10. #10
    DIY Junior Member philwgreen's Avatar
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    Ah, I see what you're saying.

    You're correct, it's currently a dry vent and transitions down to 1.5". We had debated putting another lav exactly where that vent goes up through the roof.

    It sounds like if I go ahead and put a lav there on the second floor and make it 2" I'd be ok and that would become a wet vent. Also, if I add a wye for a new lav, can the vent above that continue to be 1.5" or do I need to replace that section with 2" also?

    Am I thinking that through correctly?
    Last edited by philwgreen; 07-31-2013 at 07:56 AM.

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