Running PEX through ceiling joists

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rustic_philosopher

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Hi,

I live in NE Texas, had a house built out in the country a few years ago and I always have issues with freezing pipes in the winter. My plumbing is PEX and the main runs are in the attic. The PEX is run over the top of the joists and under insulation but there is enough insulation between the drywall and the pipes so that when we have several days below freezing, the pipe fittings will freeze and sometimes leak.

I put a wireless thermometer as a test at 2.5 off the drywall during our last cold spell and was able to confirm that at 2.5 inches off the drywall (but still under the insulation of course) the temp stayed around 50 degrees despite the attic being 10 degrees. So my plan is to re-run the pex in the attic through the joists so I can keep the pex close enough to the drywall to benefit from the residual heat from the drywall to prevent freezing fittings.

So, questions:
  1. Do anyone see a problem with the plan?
  2. Are there holed brackets that I can use to install on the joists to reinforce the location where I drill a hole for the pex to pass?
Thanks in advance
 
Residential water piping holes don't need reinforcement if you leave 2" of wood structure on the drywall side. Hole size for pex doesn't need a ton of extra room.
 
Residential water piping holes don't need reinforcement if you leave 2" of wood structure on the drywall side. Hole size for pex doesn't need a ton of extra room.
I assume you see no structural risk with what I am describing then?

If I wanted to be paranoid though, are there good brackets I could use to just offset the hole with addition strength? Some people keep telling me to not drill into the truss which I don't believe this is - just a ceiling joist but I am no expert hence my questions here :)
 
Below is a roof rafter system. The ceiling joists are usually 2x8s. These joists can be drilled keeping 2" of wood between the edge of the hole and the top and bottom of the joist.
1707701364132.png
This is a truss and often made out of 2x4s for all components. The components of a truss should not be drilled without reinforcing.
1707701993634.png

The best/easiest reinforcing is steel plate. Without doing any calculations, for a 2x4 member, I would recommend using a 3/16" plate, 3 1/2" wide and 16" long on each side of the member for like a 1" diameter hole. Use ten #10 x 1-1/2" Strong-Tie Connector Screws in each plate, staggered along the plate.

Something similar can be used to reinforce the ceiling joists if you want. A wider plate and something thinner, like 12 gauge can be used.
 
Thanks for the info!

I checked with my builder and the ceiling joists are 2x6 and he said drilling 5/8" holes in the center should not be a problem for running the 1/2" pex through.

He didn't think I needed to add reinforcement but I lean toward over engineering so I will likely look at adding reinforcement plates so it's not a point of concern as you suggest.
 
Hi, Follow up on this if I may. So I realized (I knew it but didn't really call it out I guess) that in most of the joists in question I need to drill 2 and sometimes 3 holes for the different pipes (cold, hot and mainline). For context on the mainline thing, the house has a north side and south side mainline water line with independent shut off so we can shut off south side to do work and keep water on the north side - that is why in some places there is a cold and hot line along with a mainline going to the other side of the house.

Anyways, the questions are:
  1. Does drilling the extra holes (2 or 3 - 7/8" holes vs a single hole) cause a structural concern and is there a rule around spacing between other holes?
  2. I was wondering if applying 12" mending plates / straps to the joists would be a good idea? If so, any advice on how to apply them in terms of how many, location, etc? Should I put one on each side to sandwhich the joist - or one on top only or on just one side? Does top vs bottom matter?
For additional context, the attached photo is an example of one of the areas during framing that I am intending to re-run lower through the joists.plumbing.jpeg

Thank you so much in advance for the help as I try and clear up this mental picture in preparation for me doing this the right way the first time.
 
It depends. Is that a hallway that will be finished, or a storage area, or just an attic space. And what is the spacing between the joists? It looks like it is at least 24".
 
What size are the joist. They look like 2x4 in the picture. If that's the case I would not recommend drilling without an engineering approval.
 
What size are the joist. They look like 2x4 in the picture. If that's the case I would not recommend drilling without an engineering approval.
See #5. "I checked with my builder and the ceiling joists are 2x6 and he said drilling 5/8" holes in the center should not be a problem for running the 1/2" pex through."
 
To the question about the joists - there are all 2x6.

I was mistaken partially - some of the holes needed would be 7/8 to account for 3/4 PEX. Some holes needed in some places would be for 1/2 PEX so the holes would be 5/8.

For context, that picture is back during construction - the house is done now for several years. The photo was taken from upstair in the attic during construction looking at the south end of the house along the main plumbing "artery". You can see the south side hot and cold lines terminate and turn into a bathroom on the left of the photo. On the right side, there is a single (I think 3/4) clear PEX line (ignore the numerous empty insulation sheaths) running past where the photo is to provide a cold water supply to the north side of the house.
 
For additional context, attaching a few extra photos. To understand the floorplan photo:

  1. The previous photo is looking toward the south (right side of the floorplan image)
  2. The orange line is the south side water which has a cold and hot line
  3. The purple line is a single clear cold water line running toward the north side
  4. The green line is where the clear pex line turns into a blue cold water line that splits to feed the second water heater and the regular cold water line running to the two bathrooms fed by that line
floorplan_modified.png

Looking at the "purple line" transitioning into the "green line":
landing_looking_east.jpg

Picture of the main hallway (below picture looking up at where the original photo was taken in the attic) - "orange line" on the right, "purple line" on the left:
fireplace_hallway.jpg

Picture of the master bath area (far north side of house, end of the "green line" from the floorplan drawing) from the attic landing:
master_bath.jpg
 
Just an FYI, 5/8" and 7/8" is the OD of 1/2" and 3/4" pipe. Those holes would be squeaky tight and you will most likely get noise if they even pull through. Normally we drill 1 3/8" holes and use 1/2" or 3/4" pipe insulators. If you don't want do that I would drill 3/4" and 1" holes minimum.
 
Still don't know the spacing of those joists, but as long as that is not an occupied floor, the following should provide you adequate guidance.

Holes bored in joists shall not be within 2 inches of the top or bottom of the joist, and the diameter of any such hole shall not exceed one-third the depth of the joist.

So just note that a 2x6 is 5 1/2" wide, so a 1 3/8" hole that GReynolds929 is correctly suggesting essentially needs to be centered in the 2x6.
 
Just an FYI, 5/8" and 7/8" is the OD of 1/2" and 3/4" pipe. Those holes would be squeaky tight and you will most likely get noise if they even pull through. Normally we drill 1 3/8" holes and use 1/2" or 3/4" pipe insulators. If you don't want do that I would drill 3/4" and 1" holes minimum.
Fair enough, I will plan on 1" and 3/4" assuming people here don't see a structural issue with that which is my main concern with this thread.
 
Still don't know the spacing of those joists, but as long as that is not an occupied floor, the following should provide you adequate guidance.

Holes bored in joists shall not be within 2 inches of the top or bottom of the joist, and the diameter of any such hole shall not exceed one-third the depth of the joist.

So just note that a 2x6 is 5 1/2" wide, so a 1 3/8" hole that GReynolds929 is correctly suggesting essentially needs to be centered in the 2x6.

I am pretty sure the joists are spaced 24" apart but I can double check later if needed.

When you say occupied floor, you mean the attic being a living space? Yeah, the attic is just blown insulation at this point so other than maintenance traffic in the attic, there is no living space up there.

"Holes bored in joists shall not be within 2 inches of the top or bottom of the joist, and the diameter of any such hole shall not exceed one-third the depth of the joist."

But what about the spacing from one another per my question about the multiple lines and holes? Can they be 4 inches from one another, a foot, etc in the same board?
 
I assume this is a designed house. I personally don't like 24" spacing, but if it was designed and not just a carpenter building it from scratch, then it is OK. And as this is just an attic with blown insulation, that is good.

First, it is best to drill the holes with smooth sides, no splintering. and centered in the joist. If you maintain 2" of wood between the edges of each hole, that will be fine provided the edges are smooth without any cracks. If you use a spade bit, I'd increase the spacing to 4" between the edges of each hole.
 
I assume this is a designed house. I personally don't like 24" spacing, but if it was designed and not just a carpenter building it from scratch, then it is OK. And as this is just an attic with blown insulation, that is good.

First, it is best to drill the holes with smooth sides, no splintering. and centered in the joist. If you maintain 2" of wood between the edges of each hole, that will be fine provided the edges are smooth without any cracks. If you use a spade bit, I'd increase the spacing to 4" between the edges of each hole.
By designed you mean custom? We worked with a builder to design the floorplan and the builder then used that floor plan to build it. Sorry, I may being obtuse in my understanding.

BTW I did confirm the 24" spacing - also put my leg through the ceiling in the process :/ Been one of those days...
 
First, it is best to drill the holes with smooth sides, no splintering. and centered in the joist. If you maintain 2" of wood between the edges of each hole, that will be fine provided the edges are smooth without any cracks. If you use a spade bit, I'd increase the spacing to 4" between the edges of each hole.
So to be clear:
1) Keep 2 inch from top and bottom edge of joist
2) Keep 4 inch from other holes on the horizontal plane

Is there a guide sheet you are referencing? Where does the 4" spacing come from?
 
The 2" from edge of hole to top and bottom is an established guide. The 2" from edge of hole to edge of hole I mentioned above is to provide adequate support between the top and bottom of the joist. I simply doubled that to determine the 4" edge to edge as a safety factor based on non-smooth hole.

There is a question that is often asked of engineering students. "What is the purpose of the web in an I-beam?" The answer is, "To keep the upper and lower flanges apart." In other words, the strength of an I-beam is based on the top and bottom flanges. Translating that to a joist. as long as you can keep the integrity of the top and bottom areas of the joist intact, and the center part of the 2x6 such that it maintains the separation of the top and bottom areas of the joist, you are good.
 

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