Thanks. Shoot, that sucks. So have to fully replace?

Would screwing or nailing down help at all? If the boards didn't move maybe the putty wouldn't come out the gap as easily?

Radiant and solid very rarely mix well. Live with it or redo it all, including the radiant.

So the gapping is normal for wood in a DRY home. Absolutely normal. So normal it is almost boring. Wood is hydroscopic. Which means it swells and shrinks in the presence/absence of moisture. Relative Humidity (RH) readings = airborne moisture (water vapour in the air). Most hardwood floors require a range of 35% - 60% RH forever, and ever and ever. Like, every day...all day. For 100 years.

Did you notice the word "DRY"? Excellent. Now for the GOOD news. Your reading of 38% is inside the 'allowable' range but it isn't in the HAPPY range. You want 'happy'. That means you want to increase your RH (using your whole home humidifier which is part of your very expensive HVAC system that we assume you have) to 45% (or so).

This is where in-floor radiant heat is a HUGE PITA. Many homes that have whole-home in-floor radiant heat (ie. the ONLY heat source for the home) do NOT have air vents. Which means they do not have the ability to use/add on a whole home humidifier. Nuts! Who thought of that!? Right?

And to make matters worse, heat is a DRYING force. Heat forces moisture OUT of things...this is why a 'dryer' works to quickly dry your clothes. So you have a SOURCE of heat within 1/2" (or so) of your hardwoods. And I mean every inch of your hardwood floors is sitting DIRECTLY OVER TOP of a heat source. That means every stick of moisture you put INTO the wood (by raising the Relative Humidity levels) will be forced out by the heat source sitting just below the surface of your floor.

What to do? This is where it gets painful.

1. Turn off the radiant heat in the flooring

2. Use a traditional form of heat (such as forced air or wall radiators)

3. Add in humidity throughout the home to raise the RH to 45%

OR:

1.A. Remove hardwood and replace with tile, concrete or carpet.

If you do all three things, the wood *should stop it's shrinking. The putting is still going to come out, it's just going to do it slowly. But that's what putty does.

dforootan , here are some diagrams to explain Rift & Quartered grain. Even with R&Q grain I would still suggest Engineered as a replacement. Plain Sawn grain Solid is a bad idea over Radiant Heat.

Educational Plank Flooring Examples · More Info

Educational Plank Flooring Examples · More Info

@dforootan

Sorry I missed your second question: "Would screwing or nailing down help at all? If the boards didn't move maybe the putty wouldn't come out the gap as easily?"

The method of install probably wouldn't have offered much difference. I'm assuming these floors have been glued down? The photo of the cross section is difficult to interpret.

You do NOT want to nail/staple/screw these down. Why not? Because you have radiant in-floor heat. If this is a whole-home system, you likely have hydronic tubing (water/oil/gel) sitting SOMEWHERE below the floor. If you spike that floor with pointy metal things, you run a MASSIVE risk of penetrating the tubing and causing one HECK of a mess (probably not covered under home insurance).

If you have electric radian heating wires/mats, you do NOT want to poke the floor full of holes. Why not? Because you run the risk of piercing the wiring which would cause an electric short which would either short out the system/grid (best case scenario) or cause a short that burns down your house (worst case scenario). And that would DEFINITELY not be covered under home insurance (something about homeowner negligence causing damage).

The gapping is being caused by:

1. Wrong product used (wrong cut - should have been rift sawn)

2. Wrong product used (wrong 'type' of hardwood - should have been engineered)

3. Wrong product (used in-floor radiant heat under wood)

4. Wrong type of installation (should have been floating, not permanent)

4.b. *might be the wrong adhesive used at time of install (must be viable with in-floor radiant heat)

5. Low Humidity

Since you cannot fix the first 4 1/2 issues (1-4 + b) very easily, you might as well try adding humidity. If the wood is throughout the home then you will want a whole home humidity system.

"So have to fully replace?"

No. Sorry, but it's ridiculous for an expert to state that you got the wrong wood because an area shrunk 1/32". Rift or quarter sawn wood would expand and contract less but plain sawn is perfectly acceptable. Your humidity is a bit low, close to the lower limit of what's acceptable. Will it get lower in the winter? If so, you'll need to look into a system that adds humidity to the air.

I'm Floridian so as you might expect, I'm not versed in what types of wood are acceptable over radiant heating.

Engineered is what is acceptable over hydronic radiant. Not solid. And only some engineered is allowed. Plenty of companies won’t allow that at all. And no wood at all is acceptable over electric radiant heat. It gets too hot. Hydronic only. Low temp hydronic only.

Since you wrote "Outside temp has been 70s-80s lately", I assume the radiant heating isn't currently being used. Is that correct?

Thanks all.

@Johnson Flooring Co Inc it gets cold at night so on 3 hours or so during nights

So it could possibly be a factor in the shrinkage if I'm reading correctly. Do you have alternate forms of heating? If so, maybe the floor heating should be turned off for a while. What's the outdoor humidity?

Hmmm. The duration of 'on 3 hrs at night' gives me the impression this is electric. Hydronic heating is SUPPOSED to be 'on' for the entirety of its life. It is possible to turn hydronic 'on and off' but it is to be done SLOWLY. That means 5 C per 24 hour period (or 9 F once per day).

If it 'clicks on' for only a few hours per night, I'm going to hazard a guess this is electric. Please confirm.

Do you have another form of heat for the HOME?

@SJ McCarthy - it's a water system, the thermostat kicks on the zone valve, opens it to let water circulate and then triggers the boiler to heat the water to 120 degrees. When it's off, the water is basically not circulating.

There's no other form of heating unfortunately. @Johnson Flooring Co Inc

Today outside humidity is 71% and inside 41% and temp 60 degrees

Open the windows and let the humidity in.

Is there any way to measure the temperature at the 'wood-subfloor' interface? Most floor products do NOT allow anything warmer than 85F at the subfloor-floor interface (the temperature found between the two products).

The 60 F INSIDE temperature is quite low. It is just on the very edge of "indoor living temperature". Most warranties (paint, carpet, hardwood, baseboards, doors, drywall, cabinets, etc) must have consistent indoor living conditions. The building industry has a definition of indoor living conditions (which are to be maintained throughout the life of the home...regardless if someone is home or not).

Relative Humidity: 35% - 65%

Temperature: 55F - 85F

Your indoor air temperature is only 15 Celsius. That is VERY cool. The lower temperatures have a harder time 'keeping' moisture in the air. That's why you find dew on the grass during the chill of a spring morning. The grass is colder than the air. And the air is already quite chilly. The air has a hard time 'holding on' to the water vapour. The cooler blade of grass is JUST ENOUGH to cause a water droplet to form - pulling the water from the air and onto the earth.

As the air warms up, the vapour is HAPPILY stuck in the air. That's why you have hot-sultry areas (like NYC in the summer time) and you have cold DRY areas (like Mongolia in winter). It's how the laws of physics work.

I would tip up the heating a snick and OPEN THE WINDOWS to pump up the humidity. I would bet the closer you get to 50% RH and 70 F (20 C) the better your floors will look.

Somehow you need to get the humidity and the temperature up AT THE SAME TIME.

Thanks a lot for all the comments.

So I think the takeaway here is that the wood is going to expand and shrink, and it's just not a great option for the radiant heating system. I'm not sure why it was selected in the first place. It's going to be an expensive fix having to replace it but I suppose it is what is if I'm looking for something permanent. Else sounds like monitoring temperature and humidity is the patch.

That covers the issue of the gaps forming, which on their own aren't great. But then there's the issue of the movement up and down. I feel like dealing with the gaps would be a lot easier if the boards didn't move around this gap.

Any ideas on the how to stop the movement up and down? I'm not sure why each of the floor board would go down in this area around this where the other areas don't.

The vertical movement is most likely caused by a wonky subfloor. If the previous homeowner did not PAY to have the subfloors dealt with (are you on concrete slab or over a joist system?) then the contractor would not have leveled it out. A wavy subfloor = floor that moves like a roller coaster.

Some times it is *possible to get adhesive squirted into the area where you have movement. If enough adhesive is used, it can create a build up of material underneath the wood so that there is less chance the wood will move (both the 'glue' form stops movement and the 'build up' prevents movement).

The caveat to this approach = you need to know the original glue used during install (sigh). The reason: one person's adhesive is another person's solvent.

First things first: get the temp and the humidity up and leave it there for the next two weeks. Let's see if we can get this floor to stabilize. Once the gaps close up a bit (they may never close completely...which is why there is putty there in the first place), you can then reassess what can be done to reduce the vertical movement...if anything.

Do you have extra planks of this product?

How old is the floor? If it's newish, it may still be moving due to acclimation, though wood does continue to change dimension with humidity variations. And again, the wood in your picture has probably shrunk 1/32". That's not abnormal.

@SJ McCarthy Unfortunately I don't have any extra plants.

The building was new construction in 2009. I don't know why subs wouldn't have been stabilized.

@Johnson Flooring Co Inc It would be from 2009 - still acclimating? Funny enough a bunch of other units in our HOA started having the same issues just this past month.

I think the shrinking causing the gap combined with the movement is really what's causing the headaches. The putty will probably crumble out again if I putty it back up since the wood moves up and down.

FWIW, I've been in several homes and apartments in South Korea, where underfloor heating (usually hydronic) is the standard. I assume that Korean builders know their trade, and I don't recall ever seeing a wood floor in any of those houses. I've seen lots of sheet vinyl and tile, and some carpet, but so far, no wood.

"Newish" to me would mean this would be the first time the floor has undergone seasonal changes.

You're correct about the filler not being able the stick to a moving board.