Hello,

I think this is the most appropriate forum for this question... please redirect me if not.

We are planning using a solid strip-style hardwood floor over a radiant heat system. For the most part this would be a DIY installation (of both heating and flooring). We are considering oak or maple for durability, understanding that maple has more response to moisture changes and so could be considered more risky; hence our attempt at paying close attention to details in advance.

Our location is central NY State and our house is not air conditioned. (It gets humid but not absurdly hot).

I've been reading about some of the challenges and best practices for this kind of install and wanted to share my conclusions to see if I am way off, or on the right track, and hear any useful feedback!


Here's our plan:

Construction layers (bottom up):
1. Existing concrete slab (20+ years old)
2. Moisture barrier (polyethelyene sheet?)
3. Rigid insulation + lumber sleepers / "joists" (10" OC?)
4. Aluminum heat transfer panels accomodating recessed heating tubes (something like Warmboard). This may not neccesarily require plywood subfloor, if we recess the pipes right into the insulation.
5. Hardwood floor nailed to sleepers
6. Finish (water based poly? - specific product to be determined)


Plan of action:
1. Get the radiant heating installed and run it to dry out the sleepers, subfloor, and other materials to what should be the equilibrium moisture with the normal RH for the time of year. (Not sure when this will take place but likely late summer.) Use moisture meter to track progress.

2. Introduce the flooring to the room once most/all excess moisture is out of the room and let the wood acclimate. Track drying with moisture meter.

3. Install flooring once moisture level is sufficiently close to subfloor materials (within about 2% if possible)

4. Use washer rows to form expansion joints with frequency to be determined by moisture levels at time of install (using guidelines published by NFWA for selected wood species).

5. Start in the middle and work both ways to ensure expansion towards both parallel walls.

6. Leave expansion gap under baseboard molding.

5. Sand & finish.


One specific question is whether we should prime the 5 unseen sides of each wood strip before installing, and if so, with what. Polyurethane would seem to be a plausible choice. But I have two concerns with this approach:
1. Might risk trapping moisture in the wood, or at least cause differential drying before installation since the face would not be primed, and
2. Might affect mechanical joint between adjacent boards.

Even with all the correct details, are we still taking a risk with solid floor, maple in particular?


Critiques?


Thanks so much!

Dave

PS: I guess you can tell I like lists. Hope that isn't too hard to read :}

looks good.

I will suggest the following"

1) Polyethylene Over sleepers not under

2) glue and nail sleepers.( I assume 1x4's)

3) NO MAPLE WHATSOEVER

4) strips under 31/4 if you want to nail direct to sleeper..Plank requires underlay and the wider you go the more reaction to the heating.
5) I would go Rift and quartered and you are golden.
6) no need to seal all sides, but no ill effect if you do..the moisture will be equalized already through acclimation and exposure to heat.

7) inexpensive way to prep slab will be with Karnak wood block adhesive and asphalt sealer/primer...for sleeper.
8) use 4 foot sections staggered for sleepers..not full strait runs..offset them.

9) use polyurethane...not required but theoretically better.

Hi James - thanks very much for your detailed feedback and comments! The notes about the sleepers are particularly useful as this is not something I have found much material on.

A few follow-up questions...

#6 - makes perfect sense to me. Seems like there is no point to priming/finishing whatsoever (ie not even the downward-oriented face0?

#3 - There's something about maple I don't understand. It seems to have a reputation for moving a lot and making for more difficult installations or less predictable outcomes. I'm not at all suggesting that reputation is ill-deserved; but I'm not sure I understand why it happens either. Or rather, what about maple makes it worse than oak.

I was just reading NWFA document A100 where they list a couple dozen species in order of the amount of dimensional change resulting from moisture. Maple, white oak, and red oak are all right together on that scale, the oaks in fact being slightly worse, yet I had the impression that the oaks were more favored than maple? Even cherry, another common flooring species, is only about 15% better than maple. So, is there some property other than dimensional change due to moisture that is a factor here in causing problems for maple?

(Seems like ash might be a good substitute for maple, given its better stability but roughly similar appearance...)

Thanks again

Dave

Maple runs wild in situations like this..so does cherry when it comes to under floor heating.

giv en every situation perfect there are always exceptions..follow the masses.

Maple is not ideal over radiant.

I would go quartered white.

listen.

because guidelines say one thing doesn't mean it is gospel..it means this will equate successful.

If you install by guideline your failure rate is reduced to virtually nothing.(is anything a guarantee?)

Certain wood despite hardness have inherent properties that favor situations.

Doug fir and pine favor framing lumber and exteriors..do you want oak studs and joists?

yet...oak was commonly used for building ship hulls back in the day.

so what is correct?

I can tell you maple will have a shrinkage issue over radiant..but directly to sleepers? well acclimated..all structural lumber dried.. you may prove it wrong..just live with it if your wrong.

ladtly

the reasons why tight celled lumber is bad is because their rate of loss and gain of moisture is too great..they lose it quicker than they can pull it..