Installing new hardwood over unconditioned "space"

[Diminishing Skills]

Hey everyone. New to this site and pretty new to hardwood flooring (installed once before). I'm in the process of ripping out some old crummy carpet and installing hardwood in our living room and dining room (unfinished 3/4" red oak, 2 1/4" wide). Over the living room, everything is good. I ran into an issue I'm trying to overcome when installing the hardwood in the dining room.

The dining room (11'x13') is over an unconditioned "space." It's not a crawl space. I have no access to it normally (I cut away a small section of subfloor to stick my head down there to see what is going on). I have concerns that humidity/temp may be an issue (floor is pretty cold compared to rest of house, now that carpet and padding are removed). I've read the NWFA guidelines and nothing really seems to cover this scenario. Here are some details:

1. House built in 1952. No idea when this 'room' was built. Looks original.
2. Subfloor is 5/8' ply over 1x6 planks. Both run perpendicular to joist. (There is layer of roofing felt or something similar between planks and plywood). Subfloor looks pretty good. Don't see any mold growth, warping, cupping, etc. This stuff has been here awhile.
3. The area under the room is filled with a lot of debris (I would imagine 7-8 yards of dirt, concrete, etc. The floor is not level. Just a bunch of stuff piled in the area. Removing this stuff is not really an option at this point.
4. Room is above grade.

Here is my plan of attack......what do the experts think. I already bought the wood flooring and wife is set on hard wood.....so there is no going back for me . I've hired a contractor to come sand and finish the floor (they come beginning of March and I have a lot of work to do until then)

1. Get down into the crawl space and air seal the rim joists. That is where a lot of the cold air is coming into the space. I think this will help a lot with the temp (I'm in NE Ohio, so it is pretty cold right now)
2. Insulate in between joist with R-19 (backed) fiberglass insulation. I have some of this laying around from a previous project.
3. Use 6-mil black poly to seal. I know that the guidelines say to lay the poly on the dirt floor, but not possible in this case. My thought is to tape the black poly to the cinder block walls like 1.5-2' below the joist. Use tape to hold the poly in place and use caulk to ensure it stays in place.
4. Install heated floor on top of subfloor (WarmStep from Thermosoft). (NOTE: I'm still working with mfg to find moisture barrier to install directly below heat mat).

I know this is not an ideal situation, but something I need to figure out. I figure I have moisture issue mostly figured out and heated floor will keep the flooring at a pretty consistent temperature. Any big holes here? Any major concerns.

I really appreciate any/all help. This house is a nightmare and every project is 'difficult'. I guess I should be used to it by now

 

[C.J.]

If you cut out some subfloor to see what’s going on underneath, just cut out a little more so you, or someone younger/ skinnier, can fit down there. Now you can insulate between the joists, and staple the insulation paper flaps to the underside of the joists. Then when that’s done you can lay some vapor barrier down on the ground. Climb back up through the hole and patch the hole. That’s gotta be a lot easier and better than trying to tape and caulk vapor barrier to a block wall.

 

[Diminishing Skills]

If you cut out some subfloor to see what’s going on underneath, just cut out a little more so you, or someone younger/ skinnier, can fit down there. Now you can insulate between the joists, and staple the insulation paper flaps to the underside of the joists. Then when that’s done you can lay some vapor barrier down on the ground. Climb back up through the hole and patch the hole. That’s gotta be a lot easier and better than trying to tape and caulk vapor barrier to a block wall.

I'm neither younger or skinnier anymore.....but I guess it's all relative . I will plan on insulating the joists and installing the vapor barrier (6mil black). I'll either lay on the dirt (if I can level it out).

Do you see an issue with installing a heated floor above all of this? I think it should be just fine, but just seeing if I'm overlooking anything.

Thanks for the reply! Much appreciated.

 

[C.J.]

@Mark Brown has been MIA for a bit but this is one of them things that he would be able to give some valuable insight on. Hopefully he pokes his head in and has some words of wisdom for you.

 

[Diminishing Skills]

@Mark Brown has been MIA for a bit but this is one of them things that he would be able to give some valuable insight on. Hopefully he pokes his head in and has some words of wisdom for you.

Thanks. According to the manufacturer, the heat mat is designed for nail down hard wood application (and was designed with approval? of NWFA). Just trying to make sure I don't create a "bad" environment by having a heated floor (my intent is set the floor temp at 65-70ish degrees and leave it there).

 

[C.J.]

I have no experience with under floor heating underneath hardwood. Maybe Dan has something to add? Other than that I’d say to get vapor barrier and insulation in place and let er rip.

 

[Tile Tom]

Don't quote me on this but I have always went by you don't put solid wood over in floor heat....
Normally people do an engineered hardwood if it's going over in floor heat.
Just what I was taught and always went by. Not saying it's right though.

 

[Diminishing Skills]

I have no experience with under floor heating underneath hardwood. Maybe Dan has something to add? Other than that I’d say to get vapor barrier and insulation in place and let er rip.

I tend to overthink these types of things a bit. Not wanting to make an expensive mistake. But I do think it is time to do my best and let it rip......thanks

 

[Diminishing Skills]

Don't quote me on this but I have always went by you don't put solid wood over in floor heat....
Normally people do an engineered hardwood if it's going over in floor heat.
Just what I was taught and always went by. Not saying it's right though.

Here is the product I intend to use WarmStep Mats In-Floor Heating | ThermoSoft It is not cheap by any means ($10/ft2), but think it is my best and easiest option. There are also retrofit kits that are installed under the floor (between the joists), but the prices are pretty close and I think this one is easier to install.

According to the manufacturer this product is approved for use with hard wood (including nail down). In addition, I read the NWFA's guidelines and Section 4, Appendix H covers radiant flooring. My product is going to be 2 1/4" Red Oak, so I would anticipate this being pretty stable. I will have the flooring acclimating in my house for at least 2 weeks prior to install. I don't anticipate keeping the temperature of the floor above 65-70s in the winter (Since this is directly above an unconditioned "space" the floor can get pretty cold). I'm in NE Ohio right now and with the carpet gone, the plywood subfloor is around 59 degrees give or take depending on where the temp is taken). The floor was always cold even with carpet, I can only imagine when it is just floor.

I've been talking to the mfg of the heating mat on identifying a vapor barrier to install below the mat, but not 100% satisfied with the answer just yet (I figure it needs a vapor barrier as it is above an unconditioned space. Once I get that figured, i'm guessing it will be time to pull the trigger on the mat and go for it.

 

[Steve079]

Is that mat going to be on the subfloor, but under the solid hardwood? I see you can see the wires and can nail between them, but its always been engineered only, and then on a hydro setup, not electric mat. Even with the engineered, there's only a few species that are stable enough to work.
The kicker is, that wood over floor heat is not efficient. Usually in a stained slab or with ceramic. Wood insulates, ceramic radiates...
But hey I could be wrong, and like you said, you're gonna pull the trigger and let it rip. What's the worst that could happen?

 

[Tile Tom]

Exactly! I have never heard of solid hardwood over in floor heat. I just can't picture a wire mat being under a nailed down wood floor.

I agree with what's the worst that could happen given no shop/installer is on the hook for this. It's a diy so what the hay?

 

[Diminishing Skills]

Is that mat going to be on the subfloor, but under the solid hardwood? I see you can see the wires and can nail between them, but its always been engineered only, and then on a hydro setup, not electric mat. Even with the engineered, there's only a few species that are stable enough to work.
The kicker is, that wood over floor heat is not efficient. Usually in a stained slab or with ceramic. Wood insulates, ceramic radiates...
But hey I could be wrong, and like you said, you're gonna pull the trigger and let it rip. What's the worst that could happen?

I know, it sounds weird. I’ve talked with the company and it is designed for use with hardwood. Also, radiant heat guidelines are included in NWFA.

and yes, heating mat will go directly under the hardwood. And it will take me a lot of patience to not mail through the wires too…..which I don’t usually have.

I don’t need a lot of heat. Just enough to keep the floor warm for winter months. Worst case scenario is I lose $1500 (cost of mat). Just hoping it doesn’t damage the hardwood…..fingers crossed

 

[Steve079]

I know, it sounds weird. I’ve talked with the company and it is designed for use with hardwood. Also, radiant heat guidelines are included in NWFA.

and yes, heating mat will go directly under the hardwood. And it will take me a lot of patience to not mail through the wires too…..which I don’t usually have.

I don’t need a lot of heat. Just enough to keep the floor warm for winter months. Worst case scenario is I lose $1500 (cost of mat). Just hoping it doesn’t damage the hardwood…..fingers crossed

Well, our shop has a job in the works with a floating LVP, over radiant heat. My first thought was, that's a really bad idea. But with their hydro based system, (given proper temp regualation) it will provide a very stable surface for the product. I've seen what happens to LVP in homes, such as vacation homes, where there are wide swings in temp.
With that in mind, it should provide the same for your hardwood, as long as you cant maintain a consistent humidity to go along with the stable heat, well, it sounds good in theory. I'd avoid a wall to wall install of the heating mats,(that's probably in their specs) as the start and ending rows may involve adhesive and nails in places where it may prove difficult to miss the wiring. Just make sure you are very familiar with their warranty and what it does, and does not cover. Perform due diligence in acclimating the floor, in the room, with the heat on, etc, etc, Good luck with your project