# Routing PEX through joists (?)



## joecaption (Nov 30, 2011)

No reason to not go through the joist. If this is just in a crawl space not a basement then just go under the joist.


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## dave11 (Mar 16, 2009)

Actually, its in the ceiling of a finished basement. Copper lines currently run everywhere beneath the joists, which I'd like to change, if feasible.


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## Daniel Holzman (Mar 10, 2009)

I assume you are talking about potable water, not PEX for heating. Potable water is rarely set hotter than 125 degrees F, occasionally I have seen 130 degrees F, versus hot water heat that can be 160 degrees, occasionally hotter. There is very little expansion of PEX at 125 degrees, so the hole through the joists can be slightly larger than the PEX, say 1/8 inch larger. If in any doubt, simply drop a short length of PEX into hot water, it will expand to whatever its final dimension will be very quickly, and you can test how large a hole you need.

As to the allowable dimensions for holes in joists, they are the same whether you are running wire, tubing, or just like to put holes in your joists. For 3/4 inch PEX, a 7/8 inch hole near the midpoint top to bottom of the joist should be OK, but you may want to use 1 inch to make it easier to pull. I have a fair amount of PEX run exactly that way in my basement. You can of course hang the PEX from the joists, or put it between joists if it goes that way, but if you are perpendicular to the joists and you want to hide the PEX a little, joist holes work well.


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## dave11 (Mar 16, 2009)

Daniel Holzman said:


> I assume you are talking about potable water, not PEX for heating. Potable water is rarely set hotter than 125 degrees F, occasionally I have seen 130 degrees F, versus hot water heat that can be 160 degrees, occasionally hotter. There is very little expansion of PEX at 125 degrees, so the hole through the joists can be slightly larger than the PEX, say 1/8 inch larger. If in any doubt, simply drop a short length of PEX into hot water, it will expand to whatever its final dimension will be very quickly, and you can test how large a hole you need.
> 
> As to the allowable dimensions for holes in joists, they are the same whether you are running wire, tubing, or just like to put holes in your joists. For 3/4 inch PEX, a 7/8 inch hole near the midpoint top to bottom of the joist should be OK, but you may want to use 1 inch to make it easier to pull. I have a fair amount of PEX run exactly that way in my basement. You can of course hang the PEX from the joists, or put it between joists if it goes that way, but if you are perpendicular to the joists and you want to hide the PEX a little, joist holes work well.


I mentioned expansion loops only because I found several reports online of plumbers being dinged by the building inspector for not using them, even on potable lines. 

I guess I'm still unsure of the relative pros and cons of drilling all those holes in the joists, versus running all those runners. Neither one sounds appealing. Was hoping someone who had done it could say which was preferable.


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## TheEplumber (Jul 20, 2010)

I use 1 3/8 holes for water piping up to 1"
Then I use these in the hole after the pipe is in. Wrap them over the pipe and pound them into the hole- thats why us plumbers call them pound-ins :laughing:
http://www.siouxchief.com/Support/Supply-Hangers/EZ-Glide-Tube-Insulator.80P0X


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## dave11 (Mar 16, 2009)

TheEplumber said:


> I use 1 3/8 holes for water piping up to 1"
> Then I use these in the hole after the pipe is in. Wrap them over the pipe and pound them into the hole- thats why us plumbers call them pound-ins :laughing:
> http://www.siouxchief.com/Support/Supply-Hangers/EZ-Glide-Tube-Insulator.80P0X


I had seen those pex supports and wondered about them. Seems like putting multiple 1 3/8 inch holes in every joist though would weaken them at least a little.


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## Daniel Holzman (Mar 10, 2009)

As long as you put the holes in the correct location, which is in the middle third of the joist (top to bottom), the holes hardly weaken the joists at all. This is because the middle of the joist is the neutral axis of the beam, and carries no load. A small hole centered top to bottom has a negligible effect on the strength of the joist. You can of course put the lines below the joist using hangers, but the advantage of putting them through the middle is they are less likely to be damaged by impact, and they do not reduce headroom.


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## jagans (Oct 21, 2012)

You can put a hole one third the width of the joist dead center without loss of strength. The top of the joist is in compression. The bottom is in tension. The middle is neutral. The Bang ins look nice, but not really necessary, except at the end of a run. IMO. 1/4 inch larger than the pipe OD seems fine to me. If you are going through the joists you are going to want t milwaukee right angle drill and augers with lead screw, or you will struggle. A piece of scrap 2x jiffy clamped to back up the hole allows the lead screw to pull right through the joist. Really cuts down on the sweat.


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## dave11 (Mar 16, 2009)

Are those inserts required by Code for joist penetration? It seems to me that the smooth hole left behind by a hole saw would be no rougher than the inside of those inserts. Why not let the joist support the pex on its own?

That way a smaller hole could be used (?)


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## TheEplumber (Jul 20, 2010)

dave11 said:


> Are those inserts required by Code for joist penetration? It seems to me that the smooth hole left behind by a hole saw would be no rougher than the inside of those inserts. Why not let the joist support the pex on its own?
> 
> That way a smaller hole could be used (?)


When I started apprenticing over 20yrs ago my jman handed me a hole hawg with a 1 3/8 bit(we call them water bits) and said go dill out the 3rd floor of that apartment complex. Been using one ever since.
The plugs are needed to avoid vibrations and abrasions. There are other styles too- like suspension clamps
I don't use them on every hole-


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## pexmania (Mar 11, 2021)

dave11 said:


> I had seen those pex supports and wondered about them. Seems like putting multiple 1 3/8 inch holes in every joist though would weaken them at least a little.


My thoughts exactly. I was worried about weakening it.


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## FrankWC (Nov 19, 2020)

The "pound-ins" prevent the attic or basement from having ghosts in the night. 😀


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