Expensive hardwood over radiant heat questions

Jason Horner

We're working with a client who wants to install old reclaimed first-growth hardwood plank floors over radiant heat.

We're talking about 3/4" thick x 4"-8" wide plank flooring cut from logs salvaged from river beds that sank there over 100 years ago, at about $20 sq. ft. installed.

We've never installed radiant under wide-plank antique wood before and have no knowledge of what to expect with old wood like this other than what the hardwood supplier has told us.

We're proposing a 0.5" PEX embedded in 1.5" thick gypsum layer with slab sensors, and with wooden sleepers for nailing. We think, based on our research so far, that 75F-80F will be ok surface temperature. A couple of the hardwood suppliers around have said that they'd also recommend glueing the wood down.

So my questions are:
1) How does old wood behave over radiant?
2) What do you think about wide-planks at low slab temperatures?
3) What about the effect of glue on the wood/gypsum interface?
4) Any other caveats and installation techniques?

Anybody here have experience with a long-term successful installations of this sort? I hate to be on the hook for $40,000 worth of warped hardwood.

Al Letellier

hardwood

Jason, it sounds to me that you're doing all you can to insure the life of that floor. Gather all the information you can and include it in your contract. Then, disclaim the heck out of it. You can only do so much with the information you have. Give your customer all the pros and cons of using that type of flooring and let THEM make the discission and assume the liability. Sounds to me like you're a pro who really cares about his work and your customer's comfort and satisfaction, so take it the extra mile and protect yourself. We can only do so much...

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Mark Eatherton1

The key to hardwood installations....

is to make DARNED sure that the wood is as dry and acclimated as it can be before you put it down, AND that the moisture content within the dwelling is as low and stable as possible, meaning that the gyp must be at a minimum as dry as the background humidity content.

Even with all these precautions, you can expect to see some dimensional changes in the wood. It's unavoidable unless you will have COMPLETE control over the relative humidity within the space. Generally speaking, the wider the plank, the more shrinkage you will see. Warping and cupping are a seasonal thing if you have no control over the ambient humidity within the dwelling.

If panelization takes place, as it probably would with gluing, you will end up with one BIG crack on one side or the other of the playing field. In some places, you could lose a small animal/child in some of the crevasse'...

The other problem with gluing is that gypcrete in particular is not real conducive to adhesives. It powders real easily.

As a possible alternative, I have seen the sleepers put down, then 3/4" of kiln dried plywood, THEN the wide plank hardwood floors applied. This adds an additional .75 R factor, but if you're doing tube at 8" OC in gyp, it shouldn't be insurmountable.

Another possible alternative would be to use a product like WarmBoard that has a relatively high conductivity, and or Radiant Engineering' U fin at 8" OC. In any case, protecting his wood floors is going to be a money intensive project. I'd be sure and have him sign a liability release as it pertains to the dryness of the wood. Especially if it came from the bottom of a river...

Have you considered radiant ceilings? Seriously!

ME

steve_26

humidity control

I would consider a floor system such as Stadler climate panel or Rahau I think that's how it's spelled.I've used Stadler with great results.Gypcrete much harder to control humdity it sucks up moisture in summer, use vapor barrier.
Use dehumidifier in summer through A/C sytem via Honeywell stat I think the M# T-8900 with C-Board & reheat.
Add steam humidifier for winter 40%rh.....and sign that Disclaimer.....As stated before put the floor in the space for a month.
Steve

kevin coppinger_4

flooring choice

I just did a similar job for a customer using the wirsbo quick trac system...They had old growth pine also by Carlile 14" -19" wide! I had the wood acclimate to a min of 70F for about a month and got the floor going for 3 days at no more than 82F floor temp. Carpenter installed over3 days NO tar paper, red rosin. It been running for over 1 month...they love it and no problems...thank God. I was very clear to tell they to assure that the moisture level is less than 5%...moisure and steady heat are key...god luck, it will look great I am sure..get us some pictures! kpc

Alan Bright

exotic hardwood$

9 years ago we did 1700 ft2 of radiant floor for on the main level of a 100 year old house in Denver for an old friend (YIKES). His new wife just had to have Brazilian Cherry for the
finished floor or she would just die(?), many $$$ more than the heating system(double yikes). Was on the property just a couple of weeks ago and it still looks like new (YEA). As mentioned above dried and acclimated on
site is a must! We always have floor operating 85 F water temp minimum when wood floors are going down even in summer (installers love to have heat on in July). Precise and frequent nailing with ringshanks (3" - 5"), save your money on adhesives, I have not seen any that would adhere to the dust layer that is always present even after cleaning that
seems to appear on masonary underlayment products, a product we have been using of late seems to be an exception to this conditon LEVELROCK. PL400 maybe applied to just the sleepers but can lead to outgassing when system is at design operating temps. We have almost went to blows about wood moisture content before installation begins, has to be 5% or less when installation
begins even if the average moisture content will rise after
installation, when if anything it will swell to tighten the
slats. It came to a peak several years ago when I bought my
own digital moisture meter just to protect out projects. I have
seen some oak coming from big box stores as high as 12% and
we operate in a pretty dry climate. The biggest problem is
select KILN dried hardwoods are pricey and lot's of people
in the construction chain are always trying to shave a buck
or even a nichol. I would be very careful of using any slats exceeding 6 inch in width, I would like to see the job mentioned above in 5 years with 16" & 18" planks. Sell the homeowner on a quality whole house humidifer for
winter use and get that DISCALIMER. As competent radiant installers we really have to look out for MANY OF THE FACETS OF THE JEWEL to protect our selves, the project and the end consumer.
Thanks AB

hr

I'm not sure

over gyp would be my favorite choice. The sleepers can be a hassle. The will absorb lots of water during the gyp pour, then guess what. Good chance they will shrink, cup, split, twist. etc. As any 2 by material does these days.

I, too, think the wood to Warmboard or Thermofin would be the best approch. The materials are more compatiable, and it allows much more nailing potential. As opposed to having to "hit" nailers. Nailers can be hardwood wasters, if you want joints to fall on them.

Send the owners to ALL the online hardwood sites for a good sampling of the pros and cons of hardwood over radiant. Let them hear it from the wood flooring experts.

Getting the hardwood acclimated is half the battle. keeping in in that "comfort" range, specfically humidity levels, is the challange. Wood moves in response to humidity changes. Much more so than radiant heat caused movement.

Mickey Moore at www.NOFMA.org is one of the most knowledgable hardwood techs and troubleshooters on the planet. Have the owners chat or e-mail with him.

Also www.NWFA.org

www.hardwoodcouncil.com

www.hardwooddistributors.com

hot rod

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Jason Horner

Thanks for all the great advice.

I had considered the moisture absorbtion of the sleepers - we were planning to wrap them in 6 mil poly before we laid them - we have this nifty heat sealer that would allow us to create what amounts to be a long skinny plastic bag into which we'd slide the sleepers into. We'd then screw the sleeper to the subfloor right through the 'bag' - that way all surfaces of the sleeper would be protected from moisture during the gypcrete pour.

We were spec'ing LevelRock 3500 from USG (http://gypsumsolutions.com/application.asp?app=Flooring) - USG has approved dealers install this and they warranty the installation against problems over and above what the installers provide. I like the idea of a company like USG (deep pockets) standing behind their product that way.

However the Wirsbo Quicktrak sounds like a viable option instead of gypcrete. It will have a little more 'give' too, which is a bit easier on the legs than gypcrete.

Getting the uninstalled hardwood to 5% moisture makes a lot of sense - install it snug and then let the rise to normal humitity levels in the house take care of the rest of the wood expansion. Having my own wood moisture meter is a real good idea as well - any recommendation on a make/model for one of these?

I suppose that I should have mentioned that this house is on a lakeshore, so humidity will always be present as long as the windows are open. The place will be heavily dehumidified in the summer and properly humidified in the winter. The foundation is going to be double-layer waterproofed on both the sides and under the concrete floor.

We are going to be installing a few Venmar AVS Duo 1.9 units (http://www.venmar-ventilation.com/english/avsduo.html) for heat recovery and ventilation along with their best control unit, and we'll be using hi-velocity a/c in the summer, both running with Sanuvox UV lights to kill any possible mold.

For heating, DHW, snow melt and outdoor pool heat we are using 2 ganged Viessmann Vitodens 200 boilers connected via a low loss header and the Viessmann controls to automatically rotate boiler firing.

During construction we'll be installing a hydronic air handler to heat the structure once the basement floor slab is poured (in the winter too). That way we won't be pumping the building envelope full of water vapor as is typical when using propane heaters, so the structure should be drier inside when the flooring material finally arrives on-site.


We're doing all we can to ensure that our client gets the results they want. We are actively looking at providing a strip of granite flooring in front of all the large window areas in the 'great room' and a few other rooms, isolated on their own zones from the hardwood loops, and drive the water temperature up under the stone perhaps not even having to really 'heat' the hardwood but to just warm it.

This is an ICF structure with R60 in the roof. With half a dozen people in this house and the stove going, there's probably enough heat from that alone to keep the place warm in the winter!!!

Construction will take about 6 months. I'll post pics along the way.

Keep those ideas and tips coming.

Thanks again.

GMcD

Wood floor on radiant

Instead of trying to operate a radiant floor in some really constrained conditions, why not think about installing the radiant heat in overhead panels? You get the same comfort conditions without the fear of dealing with an insulating wood floor that isn't really compatible with a heated floor system. Capillary tubes imbedded in plaster ceilings, or even suspended radiant panels integrated into drywall ceilings can be an effective solution in this case. Radiant doesn't always have to come from the floor....

Steve Whitbeck

The biggest problem I have seen with nailing down a wood floor over sleepers is the flooring guys seem to miss the sleepers on a regular basis. ( usually where you go from one row to the next.) i have a customer with an expensive cypress floor and he has had two repairs already from nail damage.

Mark Eatherton1

Avoid the 'noids...

I too used to have a lot of problems with the floor guys hitting my tubes where they went in and out of a given grid, until I got smart and started running the home runs BELOW the sub floor. They can't hit what you don't leave hanging open for them...

We use a machinists 1/2" shank 3/4" twist drill bit, drilling directly into the floor, then turn the bit sideways (while its still turning) and create the perfect entry/exit path for tube while maintaining a low profile that allows the tube to traverse without kinking or humping up out of the gyp.

It works great for WarmBoard applications too!

Some times ya just gotta be trickier than the trades you're dealing with:-)

ME

Mark Wolff

Extremely Dry

We make the flooring guy wait. After the gypcrete has been poured and set for 3 days, turn the heat on to the loops, letting the gypcrete dry out (make sure the drywall is on, obviously so the insulation doesn't soak up the moisture) and let the house sit for 7 days. Then bring the wood into the house and set it on stickers to allow the humidity to go down and the temps to even out. Then install the wood and if you put it in a little on the tight side, you should never have any problems.

As for fastening, don't waste your time with glue, it won't stick to the gypcrete (the gypcrete isn't strong enough and will come up like powder). Instead, if you need, you can set furring strips on the floor at nail patterns to keep your tubing out of the way and nail direct to them once the tubing is installed. This allows for more secure fastening than any other way, but even plywood under your hardwood will work fine.

Dry and acclimated to temp slowly are the keys to keep that wood from splitting. I would also have a disclaimer in your contract to limit liability should the above time periods not be followed.

Troy_3

Gyp,sleepers,hardwood

The way we do this is sleepers with a high strength gypsum pour. Sand the gyp and sleepers even after drying. It is a pain but the floor guys insist on a flat surface. With wide planks the floor guys around here insist on glue and nailing into sleepers. If you are concerned about dusty gyp then seal the gypsum concrete. All the gyp man. have sealer. Almost every house we do has this application. No problems yet. Sanding the gyp floor is a dusty process- beware! The #1 issue is get the moisture out before the wood comes in. And tell the floor guy it will cost $250 per repair for every tube hit. They tend to pay better attention.