Do heated floors last longer (drier - less rot)?

doughpat

I am considering doing electric radiant heated floors in a bathroom remodel that is used by short term renters (Airbnb etc.). One of the downsides to renters, as we all know, is they don't care about long-term structural damage. It is very common to find water pooled near the shower door, obviously preventable with proper use of a shower curtain (or even door), but again -- either through ignorance or apathy, the water ends up there.

I am wondering if the heating of the floor (and, in particular, subfloor) would have a substantial impact on the oh-so-common rot associated with wetness in bathrooms. Obviously the toilet area and shower/bath areas are the 'hot-spots' where rot begins.

On a side note -- since wax rings need to be kept cool, they can't benefit from the (theoretical) drying improvement. Therefore it'd be wise to consider a non-wax ring (several manufacturers now making rubber version). That way the radiant coils could go right up next to the toilet base, helping dry water that pools near there.

So what do you think -- is the drying effect significant? Do I have it all backwards (perhaps warm & wet encourages rot more than cold & wet??)?

If you can't tell, I'm looking for justification to spend too much money on an upcoming remodel....

bucksnort

Mold grows better when it's warm and damp. Wood will rot at any temp when wet.

doughpat

bucksnort said:

Mold grows better when it's warm and damp. Wood will rot at any temp when wet.

I suppose the critical question here is-does the heated floor result in a drier floor/subfloor?

If the floor is warm and wet for a short period, but overall the average moisture content is lower than it seems like it would be less hospitable for rot.

Jamie Hall

I think you will be best served by making sure that the underside of the floor is freely ventilated, and using a seamless heavy duty vinyl floor covering extending completely under the stool and shower. The stuff comes in a wide variety of designs and colours (to put it mildly!). Supplement it with a seamless vinyl baseboard molding, carefully caulked all around to the flooring and the wall.

doughpat

Jamie Hall said:

I think you will be best served by making sure that the underside of the floor is freely ventilated, and using a seamless heavy duty vinyl floor covering extending completely under the stool and shower. The stuff comes in a wide variety of designs and colours (to put it mildly!). Supplement it with a seamless vinyl baseboard molding, carefully caulked all around to the flooring and the wall.

Would you mind giving a couple of examples of this type of product?

Jamie Hall

Take yur pick...
https://www.homedepot.com/b/Flooring-Vinyl-Flooring-Vinyl-Sheet-Flooring/N-5yc1vZar9y?NCNI-5&searchRedirect=vinyl sheet flooring&semanticToken=d00r20r01122000000_202103052332449411231615958_us-east4-lqj7 d00r20r01122000000 > cnn:{0:0} cnp:{10:0} cnd:{4:0} cne:{8:0} cns:{5:0} cnx:{3:0} cnq:{0:0} cnw:{0:0} cnv:{1:4} st:{vinyl sheet flooring}:st ct:{vinyl sheet flooring}:ct tgr:{No stage info} qu:{vinyl sheet flooring}:qu

doughpat

Youngplumber said:

You need air to dry water. The warmth could help or hurt depending on air circulation. Jamie said it best once again, seal that **** up.

What about dry rot. Have you ever laid your eyes on wood that is so dried out that you can brush it apart with your fingers? I have.

It's all a balance, the rot you've seen is from something that was out of balance. 

Youngplumber said:

You need air to dry water. The warmth could help or hurt depending on air circulation. Jamie said it best once again, seal that **** up.

What about dry rot. Have you ever laid your eyes on wood that is so dried out that you can brush it apart with your fingers? I have.

It's all a balance, the rot you've seen is from something that was out of balance. 

I dont actually think I understand "dry rot" terribly well. Are you saying that just heat alone (without moisture) can cause wood to crumble?

I had always thought that some amount of moisture was a crucial part of the equation...

KC_Jones

All rot is from fungus, dry, wet, however you want to describe it, it’s always a fungus.

Jamie Hall

The wood must be moist, at least at times, for rot to occur. It's referred to as dry rot because it occurs in wood which is not in fact wet. In fact, wood which is truly wet and kept that way will not rot, as the fungus also needs oxygen and carbon dioxide to function. Wood which is kept truly dry -- below about 15 to 20 % water content -- won't rot either.

There is another form of damage to wood -- pyrolysis -- but that requires only higher temperatures -- generally quoted as above 200 F.

GroundUp

The wax ring fear is nothing but a farce. Maybe 40 years ago when everyone was running their radiant at 180 degrees all the time, but in today's world with 80-90 degree surface temps you'll never melt a ring. Think about it: how often do you see a building abandoned, foreclosed, simply unconditioned even, where the entire space is 100+ degrees? Is it a mad dash to replace wax rings every time? They won't melt until 120+ degrees which should never be attained

doughpat

Good to know about the wax ring, and yes that absolutely makes sense. Though to be honest I still think I'd consider one of the rubber alternatives. "Seems like" a superior material.

doughpat

Jamie Hall said:

I think you will be best served by making sure that the underside of the floor is freely ventilated, and using a seamless heavy duty vinyl floor covering extending completely under the stool and shower. The stuff comes in a wide variety of designs and colours (to put it mildly!). Supplement it with a seamless vinyl baseboard molding, carefully caulked all around to the flooring and the wall.

By "freely ventilated" - I would think that fiberglass batt insulation up against the subfloor (by far the most common material used in my area) would allow a small amount of air movement -- enough for water vapor to diffuse out of the cavity. Drywall, plywood, siding etc. block bulk air flow, but are probably permeable enough to allow for gradual drying.

As for the vinyl floor covering....I'm not familiar enough with it to know better, but it looks like it'd be pretty low-end on the aesthetics side of things relative to tile, no? Kinda reminds me of a modern version of linoleum?

Jamie Hall

The vinyl flooring is not really low end -- although one can get low end material in vinyl. The better ones, with cushioning and a thick vinyl layer, are very good indeed -- at least the equal of tile. I wouldn't hesitate to use the material.

In a sense they are a modern version of linoleum. Which, itself, was not to be sneered at. One of the places I care for has a linoleum kitchen floor which was installed -- over wide board single layer wood floor, not plywood -- in 1893 and is still holding up well.

Tile is all very well, and looks elegant. And is never, ever waterproof after a year or two, unless laid on a rigid surface such as concrete. Even if you manage to keep the grout lines clean -- which isn't all that easy to do, either -- it doesn't look any better than quality vinyl. That said, it can hold up well enough (unless something is dropped on it and cracks the tile) if the floor is made especially rigid -- two layers of 3/4 inch plywood on joists half again as deep as standard for the span and spacing, for instance. Also, I would hasten to add, there are places where tile is to be preferred: high traffic areas, such as entrance halls, for instance, as it does take heavy traffic better and water resistance is not a factor.

Freely ventilated does not mean fiberglass insulation up against the subfloor, unless there is an air space between the insulation and the floor. Fiberglass insulation is a sponge, and -- at least in my experience -- will hold moisture for a long long time. Leaving an air space -- or better, not insulating at all -- will do just fine to keep things dry, though. If you do use fiberglass, there are products -- usually made for roof insulation, but usable here too -- which are channels and staple up between the joists which keep the insulation away from the wood.

doughpat

Jamie Hall said:

The vinyl flooring is not really low end -- although one can get low end material in vinyl. The better ones, with cushioning and a thick vinyl layer, are very good indeed -- at least the equal of tile. I wouldn't hesitate to use the material.

Tile is all very well, and looks elegant. And is never, ever waterproof after a year or two, unless laid on a rigid surface such as concrete. Even if you manage to keep the grout lines clean -- which isn't all that easy to do, either -- it doesn't look any better than quality vinyl. That said, it can hold up well enough (unless something is dropped on it and cracks the tile) if the floor is made especially rigid -- two layers of 3/4 inch plywood on joists half again as deep as standard for the span and spacing, for instance. Also, I would hasten to add, there are places where tile is to be preferred: high traffic areas, such as entrance halls, for instance, as it does take heavy traffic better and water resistance is not a factor.

Freely ventilated does not mean fiberglass insulation up against the subfloor, unless there is an air space between the insulation and the floor. Fiberglass insulation is a sponge, and -- at least in my experience -- will hold moisture for a long long time. Leaving an air space -- or better, not insulating at all -- will do just fine to keep things dry, though. If you do use fiberglass, there are products -- usually made for roof insulation, but usable here too -- which are channels and staple up between the joists which keep the insulation away from the wood.

Lots of things learned from this post. I had no idea tile wasn't waterproof. I had assumed it was. Is the grout the weakpoint? And wouldn't tile laid on a bed of thinset that is on top of a material such as Schluter or Dietra basically providing a secondary waterproofing layer?

Cool to hear Linoleum can last that long.

I still think fiberglass insulation would allow a heated subfloor to dry. I know fiberglass is vapor permeable....part of the reason poly vapor barriers are used under drywall in cold climates -- the humid air will move through the drywall, through the fiberglass and condense on the back (cold) side of the sheathing.

Larry Weingarten

Hi @doughpat , I think @Jamie Hall had it right when early on he suggested essentially making a waterproof pan of the flooring and base so that the water couldn't ever get to the wood in the first place. Once it's wet and rot starts, it's hard to stop and fix, unless you have good access to it. It might not hurt to put some white roof coating down before your finish flooring as a way of sealing things even better. I think going a bit overboard to keep water out is going to do a better job than trying to ventilate or give it a way to dry from underneath, although belt and suspenders won't hurt anything but your wallet a little in the short term.

Yours, Larry

Jamie Hall

" Is the grout the weakpoint? And wouldn't tile laid on a bed of thinset that is on top of a material such as Schluter or Dietra basically providing a secondary waterproofing layer?"

Basically, yes -- the grout. The problem is that neither tile nor grout (nor thinset) has any appreciable tensile strength, and the bond between the grout and the tile is very weak. Any flexing (which is why I mentioned a very stiff floor!) and it will crack -- not a great visible oh my goodness crack, but a crack. And water will get through it. Yes, something like the products you mention will work -- but they will be the primary waterproofing membrane, and so must be installed with great care. The thinset will also crack.

Fibreglass is vapour permeable, as you note. But that's vapour -- not water as it might be from a leak. It will hold an astonishing amount of moisture, and unless there is good air circulation it will stay damp for weeks, even after only one decent soaking.

hot_rod

Here is what I will use on my next project, it decouples and water proofs the subfloor.

Even with a waterproof vinyl top flooring water will still get under base trim and into the sheetrock if it is puddling on the floor. In that case the entire bathroom would need to be "panned"

Or a swimming pool liner wrapped up the walls

A good quality bath mat can hold a gallon of water that splashes.

https://www.schluter.com/schluter-us/en_US/Membranes/Uncoupling-(DITRA)/Schluter®-DITRA-&-DITRA-XL/p/DITRA