Electric radiant wire in 1.5″ concrete topping?
squamishmark
| Posted in General Questions on
Hello,
Any advice on if it is ok to simply lay radiant wire (ie Nu Heat) on ply subfloor then pour 1.5″ concrete topping? Would prefer to avoid using anti-fracture membranes to keep cost down and simple. Ply subfloor will likely have 1/4″ accousti-mat underlay to reduce impact noice to suite below.
The purpose is to provide backup heat in some living areas instead of using baseboards (main heat source is mini-split).
Thanks in advance
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Check their installation instructions. Usually systems like that go directly under the tile.
I'd also check if it can go under a wood floor, concrete makes for lousy residential floors.
Why is concrete a lousy residential floor? Polished concrete (slab on grade) seems to be a very popular floor for "Pretty Good" type homes discussed here
It's hard and unforgiving. It's difficult to repair. It gets scratched. It echoes.
Plus, concrete is one of the most environmentally damaging substances you can put in a home.
I lived with painted concrete floor (slab on grade) for a year or so. Your joints and the bottoms of your feet will hate you.
Commercial buildings nearly always have concrete floors. Since most of my work is in the commercial world, I can tell you that it is MUCH less comfortable to work all day walking around on a concrete floor. Wood floors have little bit of give, and it makes a big difference even though you don't notice it right away.
Concrete is great for foundations, basement slabs, and driveways. I'd never want to use it for a residential floor. If I had no choice, I'd probably put in a layer of rigid foam under the finished flooring materials, or at least some homesote or other slightly squishable material to make the floor more comfy to walk on.
Bill
Everyone who says that concrete is uncomfortable to walk or stand on because it's hard is wrong, which is most people. Wood doesn't compress under your feet appreciably, possibly in the hundredths or thousandths of an inch, which we can't feel.
Concrete does, however, conduct heat readily and has a high heat capacity, so unless it's the same temperature or warmer than your feet, it will suck heat from your feet which is indeed uncomfortable over time, as is standing on ice or even a cold wood floor. Adding heat to the concrete helps but your feet are around 88°F and a concrete floor that temperature would bake you out of most spaces quickly. With a concrete slab floor, you will want rugs, cushy slippers and/or other methods to keep your feet warm.
A good trick I learned here is to add in-floor heat only where you will be standing or sitting for extended periods, which allows those sections of floor to be warmer than they would if the entire floor had evenly distributed heat.
Concrete floors do have high levels of up-front carbon emissions, though if you add up everything it takes to build and install a wood or tiled floor it's not that different. The primary reason I occasionally spec exposed concrete slab floors is for cost--it's the least expensive way to get a finished floor if you're starting with nothing. Because you already have floors that are framed and sheathed, I would find another system. On a current project of mine, we used Schluter's Ditra-heat system and glued an engineered wood floor over it.
I'm going to have to disagree with you here. Walking around in concrete and steel commerical buildings all day will make for more achiness in your feet and legs than walking around in a wood framed structure will. I've done both. It's really noticeable.
It's not that the wood floor material compresses under your feet, it's that the entire structure has more give and will have a very slight "bounce" to it. Basically it's not that the subfloor material (plywood/OSB) is compressible, it's that the entire structure, the subfloor, joists, etc., has just a little give where the concrete and steel structure really doesn't have any.
I haven't noticed the heat issue, but I always have work boots on with some padded sole inserts. We're usually more concerned with how warm the air in the space is. In the summer, you have never seen such single mindedness and team spirit among the trades as you get when it's a hot summer day and you want to get the air conditioning going. ALL the trades -- electrical, structural, even the GC -- is entirely on Team HVAC those days, doing whatever the mechanical contractor needs to be able to fire up the A/C and cool down the jobsite a bit :-)
Bill
Bill, I am trained in structural engineering and in the past have done calculations. There is just no way that we would feel microscopic levels of "bounce." There is on the order of 100 times more "bounce" in our shoes than in a wood-framed floor.
Concrete floors virtually always draw heat from your feet, in any season, which gets uncomfortable over time. The same thing happens if you stand for extended periods on gravel--which I did in my younger years when parking cars at fairs.
I'll defer to you on "bounce levels", as I'm an electrical engineer :-)
The aches tend to be in joints (knees, and in feet), so I'm not thinking it's from heat loss. Just going on general feel though, residential wood floor systems seem to deflect more than commercial concrete/steel floor systems if you stand in the middle and jump. I only have empirical evidence though, I've never actually tried to calculate anything. I can tell you that the Dr Scholls inserts seem to help somewhat.
Maybe I just need to spend more time doing designs and less in the field, but it's nice to get away from the desk and office...
Bill
There's more to it than that.
I think of a friend who works in a woodshop with a concrete floor, and says he knows it's time for a new pair of work shoes when his back is sore at the end of he day. I know long-distance runners who insist that concrete is harder on their joints than asphalt.
There's also a fair bit of research that standing on a heated floor all day is bad for your feet, it causes the blood to pool.
an exception to placement of radiant heat is bathrooms. It's not a place where you are standing or sitting for a long time. However, even if the ambient temperature is comfortable, the warm floor provides immediate gratification to the toes during winter months.
Thanks all but my question is about electric heating wire in concrete topping.
I am building a small multi unit building and the concrete is for sound, which will be ground flat and engineered wood on top.
Since we are talking about concrete as a flooring option - I built a mixed use building in 2005 on same property all with exposed concrete skim coat (without heat). It is a rental building and the concrete has held up beautifully. Had I used wood or another material I for sure would have had to replace it by now.
Is tubing + glycol not a better option in your case? I'm not sure what systems you're planning on, but it does seem like electric radiant heat tends to be significantly more expensive to operate in most places than using hot water.
Seconding DCcontrarian, but checking the installation instructions for your specific product is the place to start. I've only ever used those electric mats with a thinset bed.
It depends on how you're heating the water. If you're using electrical resistance to heat the water, it's the same energy cost to run wire under the floor. Wire is cheaper to run and you don't have to worry about increasing the floor thickness.
Perhaps a bit more info on the project is in order. The project is an infill building (approx 2300sf total over 4 storeys). 1st floor is open air parking, 2nd floor a 1 bedroom unit, 3rd & 4th (mezzanine) floor is a larger 2br unit. We are next to the ocean and the 1st floor is below current Flood Construction Level (FCL) requirements. No 'critical' mechanical systems can be located below the FCL but the only place for me to locate the outdoor heat pump unit is on the first floor (below the FCL). We have a mild coastal climate and our building envelope is robust (2x6 r22 walls + 2" Roxul comforat board 80) therefore our heating loads are low.
My plan is to provide some form of simple secondary heat to the units that will be located above the FCL and act as the 'critical' heat system in case downtown Squamish fills up with 12' of flood water. Our F280 room by room heat loss calcs indicate the 2nd floor unit needs 1500w and upper unit 3000w of heat in order to maintain code minimum interior design temperatures. I could do this easily with a couple of baseboards but I am pouring a concrete skimcoat anyways for sound attenuation so am thinking to add some electric heat instead.
Water/glycol system way to complicated/expensive for this application. Am doing in-floor heat in bathrooms anyways - so maybe add a matt in the kitchen area
I have done pretty close to this but with pex.
I would check with the wire mat manufacturer about direct over-pour install, I don't see how this would be much different than thinset. You can also ways thinset the mat first and do the over-pour later.
Things to watch is when the concrete gets poured there will be a lot of heavy traffic, not sure how the matt will fare. Instead of a mat, an in slab cable based setup would hold up much better.
One detail I recommend is instead of embedding the temperature sensor into the slab, run a small pex pipe (1/2" or 3/8") from near the thermostat to where the sensor needs to be and push the sensor wire into the pipe. This way if the sensor ever fails, you can simply pull it out without having to rip up the concrete.
P.S. spec double bottom plates on all walls otherwise there won't be anything to attach drywall to after the pour.