White Oak Floor on Heated Slab

[jlmccuan]

We are building a new earth sheltered home.  Dyed, stained and etched concrete slab cut 30" on bias, except in the kitchen, where my wife wants to use some very nice 36" x 18' logs cut for the flooring.  We would like to use radiant heat in the floors throughout, but could zone the kitchen area differently.  At this point, we can still do whatever as far as installation, quartersawn, straightsawn, thick, thin, long, short, t&g, bias ends, narrow and wide, whatever. Logs can be processed however needed.  Can we get it all?  Heat under the wood, minimum floor height differential from the rest of the great room?  The kitchen can be placed as a separate slab.  Home should be a fairly even environment in terms of temp and humidity.  No direct sun on the wood.  Would prefer no exposed fasteners or pegs at worst.  The wood part of the floor would amount to 200 sq ft or less with counters holding down the edges except for the 42" entryway.  Any and all help greatfully accepted.  I'd love to find we can use a rough finish on the concrete, glue the wood and leave the temp on that zone set on XX degrees year round.

Thanks much
Jim McCuan

[Den Socling]

You have a lot of questions that I am not qualified to answer but I'll see if I can get a discussion started. I would talk to somebody with a lot of experience with radiant heat. The wood should be 3/4" thick T&G. Some people want wide "planks" but widths around 3-1/4 are easier to work with. You may need a layer of wood between the concrete and the hardwood as a buffer and something to nail to. 

[red oaks lumber]

putting wood over cement is tricky any way let alone with infloor heat.there are ways to make it work. nail and glue 3/4 thick 1x2 g.treat every 16" , fill the 3/4  space with gypcrete, by doing this the heat from your tubes will still radiant upward thru the floor, with an air space the infloor might not work very well.
 having said all that, how long will the concrete need to cure so the moisture content is low enough so your floor wont swell ? i dont know. but, that answer is going to be very important.

[Magicman]

The only time that I have seen that done, the slab was lower in the kitchen area so that the finished Oak floor was level with the other "Scored" floor.  I saw the finished kitchen floor, but really don't remember exactly how it was done.  (maybe treated 2X4 joist which would mean that the slab was 4" lower)  It had a "hollow" sound when you walked on it.

And, welcome to The Forestry Forum.   

[jdtuttle]

Flooring contractors around here won't install directly on concrete especially with radiant heat. You need an engineered flooring specifically designed for your application.
jim

[coyotencuttin]

+1 on not on concrete with radiant heat. the better way would be to use raupanel system http://na.rehau.com/construction/heating...plumbing/radiant.heating/raupanel.shtml that the piping stays in a channel in the subfloor. very little chance of an accidential nail strike. it would be a mess in concrete that had finished flooring down and found later.

[Magicman]

OK, I got the answer on the application that I saw.  First, it was NOT a radiant heated floor.

The slab was recessed 1½".  Plyform was anchored to the concrete slab.  (Plyform is ¾" treated T&G plywood)  The ¾" Oak flooring was then nailed to the Plyform.

I guess that the radiant heat could be excluded from the Oak flooring portion if it was thought to be a problem?  Anyway, I just wanted to clarify the application that I was familiar with.

[Larry]

We were thinking about hardwood on radiant floors for a while.  I did a lot of investigation and it is doable if certain rules are followed.  The first is the heat has to come on slowly...seemed like over 3 days, than leave it alone for the winter.  The second if I remember correctly, is never to exceed 85 degrees in the slab.  I didn’t think we could live with those rules.  Our climate in the winter has wide temperature swings.  I’m gone at times and Kathy along with some of the family can be quite impatient when there cold.  They would crank up the thermostat without a thought.  Some of the better systems do have built in safeguards.

We are still planing hardwood on a slab...just without the radiant heat.

[jlmccuan]

OK, thanks for the input thus far.  If we exclude the radiant heat from the kitchen portion of the slab, and recess the slab to accomodate the wood ( both of which I'm willing to do ) could I run a small forced air system in the toekick of the cabinets to get that portion of the room to not add to "my feet are cold" syndrome?  Similar to the effect of the fridge, or are we back to the same problem?.  Kitchen/bar is part of a great room with cabinets all around the kitchen/bar except for a 48" walkway to get into the kitchen workspace.  I really like the idea of the wood being flush with the rest of the room's polished and scored concrete.  Wood is requested in the work area for ease of knees. 

  While working out the rest of the floor/heat question, I have some really nice white oak for the floors.  What would be good dimensions for sawing these for the intention of use in this floor?  Slab saw and rip, or slab, dry, then rip.  Any advantage to quartersawing for this use?  I have plenty, so the waste isn't as big an issue.

[PC-Urban-Sawyer]

Yes, you want to quartersaw the oak if at all possible. The truly quatersawn oak will expand and contract less across the width of the board than either flat sawn or rift sawn.

Additionally, quartersawn white oak is likely to have a good bit of the "fleck" pattern showing which is considered beautiful aqnd desireable by many people.

Another factor to consider is the width of the flooring planks. The narrower the individual plank the less change in width due to seasonal changes in humidity levels. Also, wider boards tend to cup more.

You should get the wood kiln dried to minimize problems as well.

Good luck.

Herb

[John Mc]

I know of a bunch of houses with radiant heat under a hardwood floor in my area of Vermont, but I don't know of anyone using Oak. We used White Ash at the recommendation of our builder. This was on our first floor, with a basement underneath. We wanted a slab for thermal mass, so laid foam board on top of the subfloor for insulation, then had sleepers nailed perpendicular from how the flooring would run (so we'd have something to nail the flooring to. Laid the tubing in between the sleepers, then poured lightweight concrete over the tubing up to the level of the top of the sleepers (I'm thinking this was about 1.5" thick??)

It has worked well for us. We do have to run the radiant heat fluid in the zones under the hardwood at a lower temp than where we have a bare slab in the basement or where we have tile over the lightweight slab. There is a thermocouple in the slab that keeps it from dropping below a preset temperature. This is tied into the thermostat on the wall which regulates room temp.

I don't see why the same thing won't work on your concrete slab, if you can figure out how to get something to nail into (glue would not be my choice, but I know some people install the "prefab hardwood floors with glue).

One of the keys is to pick the right species of wood for the flooring. That's why we used white ash... we were told this is one of the better hardwoods to go over radiant heat floors.

I'd bet a good radiant heat company would have a solution for you... but maybe Oak is a species that doesn't work too well? I don't know enough about it to comment.

John Mc

[jlmccuan]

Thinking out loud again, and please chime in with any thoughts.  If the section of concrete under the kitchen is a separate slab and heat zone to bring it up slowly and keep it there (if you're hot, move your feet) during the heating season.  And if recessed 1.5". Could we glue in one .75" layer of floor perpendicular to the finish grade level floor, then nail the finish grade as usual? Or would this make the whole thing worse?  Really, the floor could perhaps be treated as a rather large work mat and maybe even not run it under cabinets in this case.  Maybe I should think of this in terms of a large butcher block ?

[John Mc]

Wood is an insulator. You don't want two layers of wood. You need to find a way to get your wood flooring to lie directly on the slab. Little or no airspace, and no other layers between the floor and the slab.

There are people who are experts at this who have no doubt already solved this problem (and who could tell you whether Oak is a species you should even be considering over radiant heat in the first place). Our builder did not design the radiant heat. He went to a company that specializes in it, and they told him "this many loops of tubing in this area (different when under tile vs wood, I think) - they even told him what temperatures to set the heating water at in the various zones.

We do not leave our heat on all the time. We set it for what we want, and let the thermostat and in-floor thermocouple handle the rest. We've had no problems. I don't recall that we were even told to do anything special the first time we fired it up... we just set the temp and that was it. (Our builder was rather particular about who he bought the hardwood flooring from. He wanted to make sure it was dried properly and stored properly until we were ready to use it.)

[mooses]

I used White Oak on my Radient floor and on the ceiling/floor for the second floor, which also is Radient. But my floor was on joists. Stapled to the 3\4 ply with foil over the tubing , 10 " of ins. over the foil and 1\2" ply over the ins. I have the thermostat set at 68 and my floor moved about 1\8" to 3\16" during the winter and back to being tight during the summer. Talk to people who have instalded it, that's were I got all my questions answered and it turned out great with no problems.

[John Mc]

My white ash floor over a lightweight slab nailed to the sleepers I mentioned above stays tight year round.

[Holmes]

Radiant heating your entire slab will work. For the kitchen area if you want to make the floors the same height drop that floor 1.5"  put 3/4 sleepers down every foot and nail your floor to the sleepers. The air space under the floor will have little effect on temperature. PC- Urban-Sawyer is right on about the wood.
The concrete heat will need to be on for a few weeks to dry out the slab. You must have a good vapor barrier under the concrete slab not to mention at least 2" of solid blue or pink foam board insulation.Do not use the foil backed foam board insulation . Foil bubble bubble foil insulation can be used also, I would use it with the white vapor barrier up first,  then the foam board, 2  1" layers perpendicular to each other , wire mesh then wire tie the tubing to the wire mesh. The 5'x9' flat wire mesh panels go down easier a make for a neat pipe installation usually 12" on center.   
    1" of wood has a r value of.8 . That is not a problem for radiant heat. It is best to keep the thermostat tinkering to within 3 degrees, but you can set different zones to different temps.
   Radiant heat does not shrink floors. Lack of humidity shrinks wood.    Narrow quarter sawn wood is the best to use.
 You could put sleepers into the concrete as it is poured,that might be the easiest way to do it. I think what you want to do will be the most comfortable way to heat your house.  Holmes

[Hilltop366]

  Wood is requested in the work area for ease of knees. 

I don't think you will find wood over concrete will be any better on the knees than concrete unless there is something else in there to let the wood floor move.

Did a apartment renovation of a building a few years ago that had unheated concrete floors where the biggest problem was dampness caused by condensation from warm outside air condensating on the cooler floor even though the floor was covered with vapour barrier and carpet, we ended up using 1" blue foam with 1 x strapping over it and a layer of 3/4" t&g ply then carpet or vinyl flooring. This cured the condensation and cold floor problem with the added bonus of a very forgiving floor on the joints.

[jdtuttle]

Have you thought about staining the concrete?
http://www.concretenetwork.com/staining-concrete/
jim

[jlmccuan]

The rest of the great room will be stained and scored.  Lot's of good input folks, thanks.

Jim

[Handy Andy]

  Gymnasium floors are laid over concrete.  They use rubber pads to give the floor some "give".  I saw one laid one time, they put down the pads about every 3 feet, then 2 layers of plywood, offset, then nailed the hardwood down which held the flooring to the 2 layers of plywood,as the plywood wasn't nailed beforehand.