Engineered Hardwood and conductivity over radiant heat
We’re planning replacing the current carpet & Pergo floor finishes in the first floor of our house with engineered hardwood. This floor has staple-up (with heavy aluminum plates) radiant heat under the 3/4″ plywood subfloor (and over a crawl space).
There seem to be three choices for installing the engineered hardwood: stapling/nailing it to the subfloor, “floating”, or glued down.
We’ve installed staple-down engineered hardwood in a prior house, and it worked well. But, we didn’t have to deal with tubes full of water under the subfloor. I assume that any nails/staples would (or might!) go through the subfloor and endanger the pex tubing.
Floating floors tend to be installed over some sort of cushioning material to avoid noise, but that will add insulation in a spot where we specifically don’t want it (between the radiant heat system and the room). I also worry that the floor won’t have the “solid” feel that one expects from a wood floor.
Gluing down the floor should give it a more solid feel, and might help with heat conduction, but I’m concerned that the glue will prohibit the flooring from expanding and contracting with temperature changes.
So…how does one balance the pros and cons of the various methods? What’s the recommended way to install engineered hardwood over a staple-up radiant system? Does the answer vary depnding on the brand of flooring? We’re willing to spend a bit more on higher quality flooring if it will make a difference in the finished product.
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Replies
The answer is...
Does the answer vary depnding on the brand of flooring?
...yes. Install it as specified by the manufacturer.
If you do a floating floor, the padding is a non-issue. It's very thin and has almost no R-value. Make sure it is approved for use over heated floors.
Several comments
Staple-up radiant floor heat is the least prefered (and least efficient or effective) way to use hot water and a large flat surface for comfort heating. If during this remodel, you have the option (and the know-how, time and money) to put the tubes above the plywood, I would recommentd doing so. Depending on the design of your boiler, being able to lower the supply temperature may greatly improve the efficiency (a condensing boilker is most efficient if the return water temperatures are below 120 deg), it also may cause extra difficulty (for a non-condensing boiler, i.e. cast iron, the lower required temperature may require a mixing valve and piping changes to prevent the unit from condensing on a regular basis).
All that said, do not put staples or nails in the subfloor. Floating the floor is the prefered method. The "pad" is a small fraction of the insulation of say carpet. Also small compared to 3/4" of plywood. As recommended, check with the specific manufacturer for their recommendations.
I wouldn't hesitate to staple it down.
You aren't at risk of pentrating 3/4 inch subfloor stapling down 1/2 inch flooring with a 1-inch staple. I have had them come back around on me from deflecting off the plys in the plywood, but haven't ssen them come through the bottom.
Figure the height to the top of the staple from the bottom of the subfloor as 3/4-inch, plus 3/16-inch, for 15/16.
Now figure penetration of the 1-inch staple at the 45-degree drive angle. The cosine of 45-degrees is 0.707. So, 16/16 multiplied by 0.707 equals 11.3/16. Use 12/16 for the depth of penetration.
Then subtract the 12/16 from 15/16, for 3/16.
So, shooting the 1-inch 18 or 20-guage staples designed for engineered flooring installation, out of a dedicated engineered hardwood flooring stapler, you will be at least 3/16-inch away from the bottom surface of the subfloor.
Your call, on your place. But, I wouldn't hesitate to staple down and engineered floor in your situation. Particularly if the heating system you have is the one where the tubing slips into a track in the aluminum. I think the aluminum is thick enough to deflect the staple at an angle. Particularly in the thckened section, that holds the tubing.
PS Check on ebay and Craigs list for a good used stapler. I bought mine off ebay for around $100 dollars with shipping, and it shipped with almost 10,000 staples that the previous owner hadn't used in his install.