I have spent the last few days running my pex loosely in the floor joists with some friends. My plan was to staple up in place to the subfloor from below by myself in the evenings. But my builder said I should fasten to the joists 2” below the subfloor to avoid getting a nail puncture, (engineered I beams). What I’m wondering is, if I mark all of the floor joists and/or the tubes what is the experience of the forum with hitting a tube and needing to repair? I don’t think I want to compromise the system efficiency this much. As a potential saving grace to the joist attachment method I’m sure any potential for thermal stripping would be eliminated.

tubing 1" below subfloor, in a 2" airspace, has nearly the same output as stapled directly to the subfloor. stapled direct doesn't have enough contact area to really help very much. and in fact don't use staples: over time the tubing can chew itself up on the metal staples. You need a good standoff hanger. we like watts' "lockdown" clamps.

Thanks, good to hear from such an experienced user. I will attach to joists at the top of the web. My system was designed and laid out by a design consultant from Rehau but we didn't discuss these "details". I am using Rehau O2 barrier pipe, (low friction exterior coating) with their Talon hooks, (they are a poly hook with a nail on one side). Should go a long way to prevent tube damage and reduce noise. FYI I have 4 zones, 3/4" tube run 16" o.c in a "skip a joist" pattern. Heated and insulated finished basement below with R-12 under the tubes in the joist cavity.

that's a horrible plan. use 1/2" tubing 8" on center. You'll get better output for not much more money and it's way easier to work with.

from experience Rob seems to be quite knowledgeable........ why not recommend the plates to increase efficiency or at least lower water temperature. i have 16 inch center joists with 8 inch center 1/2 pex. with the plates i do sense a bit of "heat stripping" but who cares??? i run a GEo at about 106 degrees
and as per Rob use the "heavy plates"

ah, plate usage depends on heat load, he might not need them. but if it's a regular heat load, it's probably a good idea.

House is well insulated, modern construction. I have limited glazing on north, significant glazing on south and west sides, none on east. The house is also backed into a hill and has plenty of windbreak from trees on three sides. I don't have the loading information in front of me to give specifics but they were "calculated". I have electric heat in the basement, two propane stove inserts (one upstairs and one down in each main living space). The HDD for my house is 4200 to give an idea of the area. The intent of the radiant was to take the "chill" out of the house and keep the kitchen floor warm, using the propane stoves as the peak load offset.

   
   If you mean the top of the plywood web, you just added 1 1/2" of wood (the top flange of the I-Joist) between the heat  pipe  and the space you are heating!