2×10 vs. I-Joist with underfloor radiant
I am waffling back and forth between some brand of “I-joist” and 2×10 dimensional joists. Planning on underfloor radiant system (no slab but with heavy plates). This will require R10 minimum in the floor to force the heat up.
I’ve done a lot of reading on using I-joist but can some one give me a run down on the pros and cons of each joist in this situation?
For one I realize fiberglass doesn’t fit I-joists on 16″ centers. I’d be looking at cutting XPS to fit (perhaps put in on an angle and dropped down onto the flanges).
Are I-joists really picky on drilling a few 1″ holes for PEX and wiring? Any other issues with heating these? Do they off-gas like crazy or is that a very short half-life?
How does the weight of I-joist compare with 2×10?
Thanks in advance for any insights.
John
Edited 9/21/2009 9:16 pm by JohnWalker
Replies
I joists are great. Straight, light, environmentally friendly ( made from young trees).
They out perform 2x10s in every way.
I have used fibreglass for steel studs successfully when I have had to insulate I joists at 16 centres.
I joists have no crown so you will have a strong flat floor. Since there is no crown, if you glue and screw you will virtually eliminate squeaks.
Weyerhauser's Slilent Floor allows you to drill 1 1/2 inch holes pretty much anywhere on the flange and even have pre cut knockouts every few feet on the flange.
An I joist is probably half the weight of a 2x10. I know I've carried lots of 30 footers by myself. Try that with dimensional lumber.
The only time I use dimensional lumber since 1992 is renovating to match an existing floor. Everything new has been I joist.
Have a good day
Cliffy
Here is my first-hand report on why I-joists may be preferable, for an under-deck radiant tubing situation.
The flanges of the I-joists provide the perfect stops for the kind of insulation I used to insulate the cavities in which the tubing runs. Using foil-faced 1" R-7 closed cell foam (Thermax brand), I sliced the rigid sheets into press-fit widths, and pushed the pieces tight between flanges until they stopped against the flange bottoms.
A few air-driven nails here and there to fix a piece maybe not tight enough (play with your gun here as re pressure and depth), and you are good to go, or at least I was.
Seal up the joints, end-cut to end-cut, with that silver foil tape used for doing duct joints. Not cheap duct tape. Use the real thing.
Your tubing cavities are nicely insulated and sealed, and are a consistent 1.5" depth. Couldn't ask for more.
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"A stripe is just as real as a dadgummed flower."
Gene Davis 1920-1985
I vote I-joists. You can locate the holes at the ends right below the flange and that gets you back up under the floor quicker. Drill your holes bigger than you think you need, get a helper and watch out for kinks when your pulling the pex. I don't recommend any holes directly over the support since shear capacity of the web is borderline in many I-joists. Depending on your wall and floor loading you may have web stiffeners anyway.
Besides what has already been said, I joists don't shrink in height, so you have fewer squeaks. Since they don't shrink, the rim joists must also be non-shrinking, such as LVL type rim joist made specifically for this purpose.
If the space below the floor is also a heated space then you don't need to cover the floor fastidiously with insulation. As long as you cover the metal you'll achieve the objective.