I am running radiant pex in a 50 year old house. In the unfinished
basement the floor joists are exposed. They are 2x8.
I will have to drill a number of 1.5" holes near the ends of the
joists so that I can snake the pex around. In a new house I would not
worry about this sort of drilling.
Should I sister (maybe 3 foot spans of 2x8) the joists that I am going
Unless you plan to finish the ceiling, or lack head room, why not just
run a 1x4 across the joists and use the approved staples / hangers for
the pex to attach it to the board. Seems much easier and wont damage
the structure. And what size PEX are you using to need a 1.5" hole?
Most PEX is 1/2" or 3/4".
I'd avoid drilling if at all possible. 1x4's are cheap enough and the
job will be easier than drilling all those holes with a slow hole saw,
plus you'll likely need an angle drill to get between the joists.
You could also use copper pipe and not need any boards, just use a
pipe hanger every 4 to 6 feet.
By the way, is PEX approved for radiant heating? I'm just asking, I
have never installed radiant heating, or used PEX for anything. I
only use metallic pipe for plumbing. They claim PEX will last years,
but I'll wait to see if their claims are true before risking a flood
in my house. Plastics prove to be a poor lasting material for most
other things, so I wont use it. I'd rather spend the extra $ and get
something that I know will last for years, like copper pipe.
3/8" pex. It is a loop and runs back and forth. So this means 3/4"
of pex. I do not want to have squeaks.
There is a headroom issue in that the ceiling is fine but not super
high. You are right about an angle drill.
I'm kinda waiting to see what happens with all the Fire Sprinklers installed
in these new houses in California. They use plastic and it's under very
high pressure. I have drilled through it and what a pain to get it fixed
and find the shut offs. Even the water valve/meter at the street didn't
shut it down..
"You can lead them to LINUX
but you can\'t make them THINK"
Pay attention to your pex (papers) any inside radius turn is where you
make the bend, Not some big hole in the lumber. Mouse told the
elephant - if it don't fit don't force it.
Study the install methods, minimum.
A joist is a beam. Sistering means you put another beam in parallel for
the full length.
If you suspect there will be a structural issue why not have someone
take a look?
You made a good choice with the underfloor radiant. I installed it in
our house and it works great. Its a pleasure to walk on a warm floor on
a cold day.
In general a 1.5" hole in a 2x8 is okay IF dilled in the center
(verticle) of the joist and near the ends. However, an old house with
2x8s may have been underengineered to begin with. Any doubts ask your
For 3/8" pex, you don't need a 1.5" hole, a 3/4" hole should be fine.
If you need to cross a joist twice, use two holes, side by side. Two
3/4" holes side by side impacts the strength of a beam less than a
Prescriptive rules for wood framing would certainly allow a 3/4" hole
in the proper location on a 2x8 joist. The proper location means away
from the bearing ends laterally (say at least 12" from the supports)
and within the middle half of the height of the joist. So that would
likely be fine.
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