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Old 02-10-2015, 09:00 AM   #1
Teri-Lee
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Layering up a radiant heated tile floor

Hello I'm a DIY weekend warrior and I've been a huge fan of this forum for many years. It's helped me figure out four bathrooms (with 2 tub surrounds and 2 custom showers) as well as 2 kitchens. Currently working on another shower, but I digress.

Hubby and I would like to do a major reno of the old half of our current home. That half was originally a cabin from the 50's. Un-insulated floor over dirt crawlspace. One challenge is that the existing tiles just clear the exterior doors, so height is a concern.

Whilst working on the current project we decided to pull up some tile to check the condition of the subfloor. All dry, no rot. But we were a bit surprised by the layers (see pic)
1x6 planks sitting on joists (joists 24" apart)
Tar paper
5/8" tongue and groove hardwood
1/4" mystery pressboard
2 layers stylin' linoleum
3/8" plywood
Tile

We would like to instal hydronics (gas heater for costs and energy efficiency). The planks seem rock solid. We were thinking of going down to them and building up like this:
1x6 planks (original)
1/4" plywood (to deal with gaps)
PEX 1/2" (does it come any narrower?)
SLC to cover + 1/2"
Modified thinset
Decoupler
Un modified thinset
Tile

Will this fit or am I dreaming? We have 2" to work with if we go down to the planks. I've never done a heated floor, nor have I ever had to worry about height.

Also, not sure if this is structurally sound enough, or how insulation might possibly fit. We're in Vancouver, Canada - rain forest, fairly mild winters. Surviving without insulation so far. Don't want to spend a lot to heat the crawlspace though.

We would like to go hydronics and then continue this through to the newer side of the house over time.

What do you think?
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Old 02-10-2015, 09:06 AM   #2
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why not run the tubes in a "nail up" from the under side between the joist?
That could save you some dollars and space.You would add insulation from below.
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Old 02-10-2015, 09:42 AM   #3
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Welcome back, Terri-Lee.

If you'll add that geographic location to your User Profile it'll remain in permanent view to help in answering some types of questions.

The absolute minimum you must install over your board subfloor is nominal 1/2" exterior glue plywood with no face of grade lower than C. And with your joist spacing I'd recommend it be thicker.

Your plan to put hydronic tubing covered with SLC is only recognized by industry standards for joist spacing not to exceed 16" on center. You could elect to use it anyway (gonna be spendy) if you want, but..........

But before you decide on anything I recommend you evaluate your joist system to see if the floor will even qualify for a ceramic tile installation without some help. You'll be adding a good deal of dead load to that floor with your planned installation.

You can enter information into our Deflectolator in the dark blue bar above to get you started on that.

My opinion; worth price charged.
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Old 02-10-2015, 10:30 AM   #4
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ASSUMING your structure doesn't quite meet L/360 for ceramic or L/720 for stone, an idea might be to pull up the solid wood planks and then see if you can put joists between your existing 24" oc to get 12" oc

Once the solid wood planks are gone, you could go with an appropriate 3/4" plywood or OSB over your new joist structure.

This will give you a nice solid foundation to build upon.

Even if your joist structure is okay, it might not be a bad idea to pull the solid wood planks anyway...you'll gain some extra height to work with I think. No tile or stone or hydronic systems like solid wood floors because they move too much.
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Old 02-10-2015, 11:19 PM   #5
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Thanks for the suggestion about installing the PEX from the bottom. I've read a number of other posts about that approach. It would work under the "newer" part of our house where the crawlspace is 4' high. Unfortunately the older part has very little clearance (less than a foot from bottom of the joists to the dirt). We spent a weekend tunnelling under it when we hooked up to city sewer - I was lead mole pushing the dirt back and my husband dragged it out. Worked for a run straight in, but I sure as hell wouldn't want to try to cover the whole floor that way!

I'll have to check out the deflectolator, CX. I have a hunch I'll need to add support. Sigh. At least I have time to figure it all out.

Chris, would Douglas fir planks move much? My husband is pretty sure that's what is down there.
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Old 02-10-2015, 11:32 PM   #6
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Teri-Lee, are the planks perpendicular to the joists or do they run diagonally?
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Old 02-10-2015, 11:43 PM   #7
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Planks definitely run perpendicular to the joists.

Ran the numbers through the Deflecto machine, and it spit out L/511. Good for ceramic but not natural stone. Where does porcelain fit? And assuming it could take the weight, if we wanted to go stone would we add another layer of subfloor, or would we have to beef up the joists themselves?
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Old 02-10-2015, 11:58 PM   #8
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If you use porcelain, it's the same as ceramic, so the minimum is L/360.

For natural stone, you'd need to meet L/720, so the joists would definitely need some strengthening.

Since your planks run perpendicular, you could get by with a layer of 1/2" ply on top of them, but 5/8" would be best since you have 24" joist spacing.
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Old 02-11-2015, 07:04 AM   #9
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Quote:
Originally Posted by Teri-Lee
Un-insulated floor over dirt crawlspace.
...gas heater for costs and energy efficiency
Seems to me you might want to start with a thick layer of appropriate insulation. Which might affect plumbing, hydronic heating, and ventilation.
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Old 02-11-2015, 10:47 AM   #10
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Thanks for the suggestion of 5/8" ply, Kevin. I think hydronic heating is out because of the height issue plus the extra load is a big question mark.

Now leaning towards electric radiant. I really like the idea about pushing heat cable through Ditra that I read about in this thread:
http://www.johnbridge.com/vbulletin/...light=Hydronic

Larry - for insulation I can't get under the joists. I have seen posts about putting down a layer of cork. Sounds like it might be thin. Not sure about cost. Would this be a good option? And I'm not sure where it would go

So here is what I'm thinking now in terms of layers:
1x6 planks (original)
Vapour barrier (nothing currently down there)
5/8" plywood
Cork insulation???
Do I need another layer of ply here?
Modified thinset
Ditra with heat cable (per other post)
SLC
Tile

Would love to hear your thoughts on the question marks!
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Old 02-11-2015, 02:07 PM   #11
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Now that you think your height issues are mute, you could leave your 1x6 planks down. BTW, to address your question, solid wood moves MORE than plywood or OSB regardless of the species. That is the nature of solid wood. That kind of movement is not appreciated by items that dry hard and stiff like cement and thinset and tiles unless steps are taken to isolate them from moving wood. Adding plywood on top of the solid wood is a step in the right direction, as Kevin suggested. The thicker you can go with the plywood, the better for your floor so if 3/4" could fit, consider it.

Ditra-Heat is awesome. I have it in my master bathroom. Feel free to peruse the link below my signature. Ditra-Heat is 1/4" thick plus thinset.

So for your floor, I think I would do:

1x6
Not too sure about your vapor barrier here...I don't think this is the right place for it but I could be wrong. The best place is actually on the soil in your crawlspace or under the 1x6 planks. This is also the best place to put insulation. Maybe you should still remove the 1x6 and insulate under them and then replace with 3/4"?
3/4" OSB or appropriate plywood (C face or better, exposure 1 rating) or 1/2" or 5/8" depending upon height constraints or if you removed the 1x6s.
SLC if you need it.
Modified thinset
Ditra-Heat
Unmodified thinset
Tile
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Old 02-11-2015, 03:04 PM   #12
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Quote:
Originally Posted by Teri-Lee
I have seen posts about putting down a layer of cork. Sounds like it might be thin.
It depends on which website you believe but it doesn't appear that cork is much better at insulating than plywood. Which implies you would be better using thicker plywood so you could get some marginal gain in stiffness and probably save some cost.

Looks like an inch of plywood has an R-value around 1 (maybe a little more). Oak Ridge National Laboratories has a calculator for recommending R-values here. Based on Blaine, WA (almost Vancouver) and not thinking about the details too closely, it looks like they recommend R25. That sounds really far away from your existing conditions. Don't forget to consider moisture and air flow effects when considering insulation.
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Old 02-11-2015, 05:48 PM   #13
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Terri Lee, you do not want any sort of "vapor barrier," nor anything else for that matter, between your board subfloor and the added plywood subfloor. If you have a moisture problem you need to deal with that below the subfloor structure as Chris points out.

I agree with Larry about the cork.
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Old 02-12-2015, 09:22 AM   #14
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No, CX, there are no moisture issues down there. It just seemed odd not to see any vapour barrier. Unless that's what the tar paper was supposed to do.

We have thought about the alternate approach of sealing off and insulating the crawlspace itself (treating it like part if the indoor space). More scope creep. But this would be the time to do it!

Thanks for the info about cork and the link for R values, Larry. Good thing we have time to figure that angle out. I was wondering why the floor wasn't colder given the current lack of insulation - but now that I've seen how many inches of material is layered down, I can see that it provided a degree of insulation.

Chris, that's an amazing bathroom reno - absolutely stunning. And I've looked at ditra heat, but we're willing to spend time with a spool of wire and regular ditra if we can save some money. Cheap and cheerful, and if my tootsies are warm in the end I'm happy! Besides the other part of our major reno will be new kitchen cabinets. Not cheap.
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Old 02-12-2015, 09:26 AM   #15
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It is common to use roofing felt or builder's paper between the subfloor and nail-down hardwood flooring to help allow independent movement and prevent squeaks, Teri Lee, but for structural subflooring you don't want anything in there.

My opinion; worth price charged.
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