Tag Archives: pex tubing

PEX and Rebar Hairpins

PEX and Rebar Hairpins

Reader BRIAN in LEROY writes:

“I want hydronic floor w/ PEX embedded into concrete slab on grade at MN-IA area. Blogs show rebar through holes in poles that are bent into the concrete at about 45 degree angles presumably to tie all elements of building envelope firmly together. In this area, code is for post holes to be about 4′ deep and with R10 foam 2′ down at the edges. Is the rebar into the slab still necessary? Advisable? If yes, for a 3.5″ slab how do you recommend aligning the PEX tubes with the rebar? I assume the rebar needs to be roughly centered in the slab to have the intended strength. PEX is recommended about midway in the slab, too. Even if PEX were below the rebar, is there some risk of future leaks due to proximity or direct contact between PEX and rebar?”

Rebar hairpins are specified for eave sidewall columns only, in order to create what is known as a constrained condition (read more here: https://www.hansenpolebuildings.com/2018/11/importance-of-constrained-posts/).

On your particular building, if your order is placed assuming “no concrete floor”, your building dimensions are such as for wind shear loads to not be an issue and plans will be engineered without hairpins.

In answer to your question about future leaks due to PEX and rebar being in close proximity or touching – rebar can have some sharp pieces potentially damage PEX. PEX can be tied to rebar in such a way so it doesn’t come in actual contact with rebar. Once slab is poured and everything is locked in place, all should be good even if PEX does contacts rebar. Always pressurize PEX with air prior to pour and leave pressurized until system gets purged and filled with water to make sure PEX doesn’t get damaged by any other trades during construction phase. You are more likely to experience damage to PEX if you don’t properly sleeve where PEX goes through control joints and these open up enough to cause problems later. PEX should have a 200-300 year life expectancy in a concrete slab according to PEX companies.

Running in Concrete Slab PEX Inside Large Tubing

Running in Concrete Slab PEX Inside Large Tubing

Credit for writing this guest post goes to my friend and radiant floor heat expert Les Graham www.RadiantOutfitters.com. If you prefer your DIY radiant floor heat to be right, rather than cheap, call Les 1.320.212.0863.

Question from Mike the Pole Barn Guru: Is it beneficial to place radiant floor tubing inside a larger diameter tubing in concrete, so the actual heating tubing could be replaced in the event of a leak?

Les: In my thirty some years in radiant floor heat I don’t remember ever getting this question before. I thought I’d been asked all that could be asked related to radiant floor heat.

My quick answer is “NO.”

There are several things to consider here:

  • I strongly assume a person would find it VERY difficult to actually place a smaller tube inside a larger tube!
  • I don’t like Big tubing in concrete as it could weaken concrete.
  • With plain Pex products and their poor “Coefficient of Linear Thermal Expansion” (regular Pex grows like crazy when you increase its temp with boiler water) will the movement of the inner tubing cause thin spots eventually in itself? There could also be the threat of “Noise” from plastic fighting plastic from the movement.
  • Many plain Pex products have their O2 barriers on the outside of their tubing. Again as above, the movement of regular Pex would sacrifice their outer O2 barrier.
  • Whether dealing with a Pex-Al-Pex tubing or plain Pex you want the tubing in direct contact with the concrete to give you the best “Heat Transfer.”
  • I highly doubt with all the 90 -180 degree turns, that pulling the inner tubing out later would be possible, let alone getting the replacement loop back in!?
  • Future leaks in floor tubing happen VERY rarely. Drill bits are the main culprit. Most people chisel down and place a coupler in to fix it. Sometimes you can simply take that loop off the manifolds and still heat the project successfully.

These answers come from my personal experience/opinions. I have never seen any trade articles or been to any radiant floor training that covered this subject.

Building After a Burn Down

Building After a Burn Down

Western United States wildfires have been featured on network newscasts and seen in our air for months. My own Auntie Norma’s home was a victim of California’s 2018 Camp Fire – where she lost all of her worldly possessions.

Reader MATHEW in RENO writes:

“Greetings, I know I’m not the only person thinking this. Every day it is so smoky I can barely see the sun. After a house burns down, won’t the lot still have the utilities? The electrical service may need to be replaced if it is overhead, but that can be done. Water and sewage should be existing. I cannot afford to buy my son a house with the current costs, but I might be able to afford a lot with existing utilities. Do you offer a kit that is sort of like a beach house (elevated enough to park under). A elevated single story (2 bedroom, 2 bath and a big balcony) would be good. It might have paving stones for the garage floor. It might have a chain link fence with the internal slats to secure the garage. I saw somewhere that offered a concrete sleeve for poles (it was meant to keep dock pilings from rotting out), could this be used for fire proofing? Anything that is built needs to meet code. We all have seen the sad story of “Phonehenge” (youtube). If you build anything these days, you buy a “section”. Home Depot and Lowes offer prebuilt roof trusses and Zip Systems offers prebuilt 6 X 8 wall sections with framing and insulation. If I rented a LULL I could probably lift the sections in place. I would hire a experienced utility operator to set the poles. A laser level is a good friend. When I used to work, we never called anything “cheap”, it was “value engineering”. The floor joists could be “engineered wood beams”. The floor could be something like 5/8″ T1-11. I have heard ugly stories about outgassing from closed cell foam, but I think I could get about a 1″ spray under the floor to insulate. We have “earthquakes” out here and I think that vinyl flooring might survive a “shake” better than tile. PEX plumbing and maybe a solar panel or two to charge the cell phones when the fires are back. Feel free to share and use any of these ideas, I just cannot bear the thought of spending 300K for a 15 year old doublewide on a 1/10 acre lot here. My son and I have looked and even in New Mexico, there is no property that is worth buying. No Rush.”

Mike the Pole Barn Guru responds: 

Even here in NE South Dakota, over 1500 miles away, we have had days of smoky haze.

Here are a few answers to your questions: you are correct about underground utilities remaining in place however they should be carefully inspected for any possible damage prior to reuse. We most certainly do provide what are known as stilt houses. Plastic sleeves used for fear of properly pressure preservative treated wood decaying prematurely when columns are placed in ground would not protect from fire proofing. If columns were large enough (roughly a 10×10) they should resist an ASTM E119 fire exposure for an hour, however it may be less expensive (and certainly easier to work with) to wrap them with two layers of 5/8″ Type X drywall and then cover with steel trim.

Your area is in Climate Zone 5 – meaning underfloor insulation would need to be a minimum of R-30. As you will need to protect the underside of your floor system from fire, you might consider using Rockwool batt insulation (it will not burn and is unaffected by moisture) with steel panels underneath.

There is a Building Code (2018 International Wildland Urban Interface Code or IWUIC) specifically addressing areas of concern when building in potential wildfire areas. It can be found at www.codes.iccsafe.org/content/IWUIC2018/effective-use-of-the-international-wildland-urban-interface-code.

Avoid Pex Tubing When Attaching Interior Walls

Slabs on grade are highly popular for barndominiums, shop houses (aka shouses), post frame homes, garages and shops. Many (mine included) use radiant in slab heat, meaning there will be PEX tubes in the floor to be avoided when attaching framed interior walls.

Reader STEVEN in AKRON writes:

“My wife and I are looking to build if we get some land. I would like to build a barndominium. How do you know when putting up the walls that you are not going into the radiant heat in the floor?

I am sure I will have more questions later.”

Mike the Pole Barn Guru says:

This article may prove helpful as you begin your barndominium journey: https://www.hansenpolebuildings.com/2021/02/a-shortlist-for-smooth-barndominium-sailing/.

In Floor Heat System InstallationWhile I always recommend you closely follow layout plans with your tubes and take photos of tube placements prior to pouring, neither of these is a guarantee of missing tubes. You could rent a thermal imaging device to find your tubes, or do it in a more low-tech fashion: turn heat on high and once heated mop water over the entire floor surface. Areas drying first are tube locations. Use chalk to mark them. 

Radiant heat tubing in a concrete slab needs to be closer to the slab top than bottom, normally in the upper two inches of concrete. Proper anchorage to a slab has fasteners penetrating at least an inch into concrete. If you can guarantee your pex tubing will be no closer to the top of the slab than say an inch and one-half, you could use 2-1/2″ Ramset nails.

Personally, I prefer using Tapcon screws 

What you’ll need:

  • Tapcon screws – Be sure to get
    ones with hex heads. Don’t try to use a flat-head screwdriver to drive them!  3/16″ x 2-3/4″ screws will be getting you very close to your pex tubes,
  • A hammer drill
  • Several concrete drill bits
  • A hex head bit for drill fitting Tapcon head size 

How to attach walls using Tapcon screws

  1. Drill pilot hole
  • Drill a hole through 2×4 bottom plate center, every 16″ to 20″ inches.
  • Hold the bottom plate in place by standing on it if possible.
  • Use firm pressure, but don’t push too hard. Save your body, drill will do the work!
  • If using 2 3/4″ screws, put a piece of tape on bit 3″ from tip. (Drill 1/4″ deeper than depth of anchor plus 1 1/2″ for bottom plate.)
  1. Attach screw
  • For best results use a hex-head attachment on your power drill to secure screw. (Even the correct size flat-head screwdriver attachment will slip off frequently.)
  • Start off slowly until you’re through the bottom plate.
  • Speed up drill and drive anchor deep enough into concrete so the screw head is flush with bottom plate.

Make sure you have enough drill bits on hand. You’ll go through several as tips eventually wear out or break off. Repeat this process with each wall section.

Another method of attachment entirely avoids penetrating your concrete – construction adhesive. Make sure the slab is thoroughly clean and use a polyurethane adhesive. Polyurethane works if there is any moisture in the concrete or bottom plate and it has gap filling properties.

Please reach out to me any time with questions.

PEX-AL-PEX Tubing for Post Frame Concrete Slabs

PEX-AL-PEX Tubing For Post Frame Concrete Slabs

Long time readers will recall my prior article on PEX tubing for post frame concrete slabs: https://www.hansenpolebuildings.com/2016/08/pex-tubing/.

I caught up with my friend Les Graham of Radiant Outfitters at the recent NFBA (National Frame Building Association) Expo in Louisville, who I volunteered to do a nice video in regards to better floor tubing and better floor heat.

Besides providing your complete post frame building kit package, Hansen Pole Buildings can also provide a complete kit package for your radiant floor with everything you will need to get your system into a concrete slab on grade (including layout drawings and instructions).  Talk to your Hansen Pole Buildings’ Designer at (866)200-9657.

Minimizing Excavation in Post Frame Buildings

Minimizing Excavation In Combination With Post-Frame Frost Protected Shallow Foundations

Regular readers of this column recognize a groundswell movement towards energy efficient post frame building design.

Reader (and Mechanical Engineer) DAVID in CONNECTICUT had some thoughts (after reading a volume of my article pages) in regards to FPSF (Frost Protected Shallow Foundations) and radiant in floor heat.

He writes:

Good Morning, Mike!

In regards to this post, I’m having a lot of trouble understanding just how this all fits together…


Firstly, I have read thru many (if not all) of your blog posts about foundations/slabs, browsed more than 40 pages of 80 blog list pages, as well as plenty of external references.  Thanks for all the info you’ve put up!  So trust me I’m not just trolling and looking for inconsistencies, just trying to get the best understanding possible before building and hoping to condense some of the knowledge that is spread through your blogs.  I‘m a mechanical engineer by trade but my thoughts stray into many other areas!  Because of your focus on engineering, Hansen is a front runner for getting my money.  Also, I thought maybe I could contribute to the evolution of your build process to make things easier for the insulated slab folks here in frost country!  I am in CT, frost and cold are an issue for heating my near-future garage.  I’d like to run PEX in slab, and r10 foam under slab was recommended for max efficiency. How to install PEX Tubing in a concrete slab I’ll also likely be doing at least a partial FPSF at the edges.

In your blogs there seems to be a little bit of conflict on what you recommend for site prep. 

  1. Here, in the “thoughts” section at the bottom,  https://www.hansenpolebuildings.com/2011/11/soil-compaction-how-to/ you recommend the gravel go in after the posts, but that seems to require plenty of back excavation to get the recommended gravel depth.  How is the builder supposed to remove 6+ inches of ground from underneath and not disturb the soil under the skirt board?  Plus, in the case of the people to do have gravel put in, you just spent all that effort putting it in and compacting it now you have to dig it out?
  2. What I read at the “concrete slab -3” link above seems to indicate that I do organic removal, use at least 6”of properly compacted crushed processed stone to bring it back to (or just above) the previous grade, build the structure with skirt/splash board on that grade.  Then for a 4” slab, re-excavate down 2 more inches for the insulation/ vapor barrier.  That might be fine, but you also mention “prior to pouring (concrete),” use 2-6 inches of sand/ sandy gravel below the vapor barrier and 3-4 inches of sand above it.  That would be a minimum of 5 additional inches (+2 for foam= 7”) of internal excavation after building!  Or did you mean the first layer of sandy gravel would go on-grade and be built on?  That’s still 5 total inches of post-build excavation (3 more of sand + 2″ of insulation board).  Something still doesn’t quite add up.  Not to mention the effort/ difficulty of re-leveling and re-tamping the internal excavated surface again!
  3. You specifically mention in several places never to exceed 3.5” up the 2×8 skirt board, which is also fine, but what if we look into deeper slabs and less work to excavate?  What if we did all the gravel/sand down 2” from FINAL grade, and used a 2×10 ground contact skirt board? Then there would be no interior excavating.   I designate “final” grade because the area would be leveled, then building built and 2” backfilled against the skirt.  OR in the case of a FPSF, the vertical insulation would be there anyhow.  If there must be 2” of sandy mix above and below the vapor barrier you could use a 2 x12 skirt, right?

4. Also this article recommends against sand pre-pour.  https://www.concreteconstruction.net/how-to/site-prep/subgrades-and-subbases-for-slabs_o Thoughts on that?

5. Lastly, I had an idea to more easily prep the area for both insulated slabs and FPSF. This also prevents disturbance of the sub-grade area during the install of the FPSF external insulation.  Please see the illustration below.

6. Prep the area with appropriate sub-base compacted gravel but at a lower than “finished grade” level.  This would be an area consisting of the building size plus 3 to 5 feet in each direction.

7. Install the poles and footers.

8. Install the 2 x12 skirt board on surface of the lower than final grade area.

9. Trench the outside for the vertical and horizontal FPSF insulation,

Backfill in lifts, compact, and re-grade the area outside the skirt board insulation.  This supports the subgrade area UNDER the skirt board and behind the insulation so you don’t accidentally leave voids behind it.

THEN you add and compact the material inside the skirt board like sand/ stone-dust, vapor barrier, insulation foam, rebar and PEX tubing.  This prevents weakening of the material under the skirtboard as well, because it’s never disturbed!

Last you pour 4” of concrete leaving a 3.5” reveal and you have the same  post length, siding material and eave height/ clear height as before.

Can you even get 2 x 12s treated that might work in this application?  Is UC-4B needed as it’s not exactly structural, right?  Plus it’s surrounded by foam and well drained soil.

I know this is long, I apologize again, but I appreciate your careful review and answer in advance! 

Thanks, and I can’t wait to hear your thoughts!  Feel free to edit/ take snippets out for another FPSF blog post if it’s helpful.  The post to end all FPSF/ slab prep/ frost blog posts!  Honestly, 80 pages of blog post lists is very cumbersome.  I’m thinking a digest of some kind is in order!

Mike the Pole Barn Guru responds:

Tune in to our next episode for a thrilling (and simple) conclusion!