underfloor heating causes black mold on skirting boards

flooringissues

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Hi,

I am moving into a new house soon, and it will have underfloor heating throughout ground floor.
System is water based, pipes embedded in concrete screed.

The builder has told us we can not put down wooden flooring of any type.
The wood acts an insulator and will cause black mold to form on the skirting boards.

He advised us that tile is best, but can even use carpet or vinyl.

I have no experience of UFH systems, but it seems strange to me that carpet is ok to use and wood is not. Especially since both choices have very similar tog values.

Has anyone experience of putting down wooden floors and then having problems with mold forming?
 
I know someone who has UFH on the ground floor of a house built about 6 years now. He has engineered oak floors everywhere except the bathrooms and has solid oak skirting everywhere. No issues with the floors or mould that I am aware of.

There are lots of articles on google about UFH and wooden floors, for example this one from a large manufacturer of wooden flooring. [broken link removed]
 
That is interesting JohnJay, as builder told us since its a new houes, a3 rating, it's super warm
and that will cause black mold to form quicker than seen in older houses.

I have found a lot of material online about it... but i don't know who to trust.
I go on to one website and it states you can't use hardwood, the next says you can.
Often the websites are sellers or have some interest in pushing their agenda/viewpoint,
so I am not sure I can take them at their word!

Go to a carpet retailer website, and they say carpet is great
go to wood one, and they say wood is fine.

One independent (seemingly) said that wood could be used but had to be very cautious to prevent moisture
damage. i.e. let the subfloor and wood acclimatise over a few weeks.

So just interested in any real world experience people have had with it.
 
Well unfortunately I can call myself something of an expert on black mould, though not in connection with underfloor heating.

"Astonish" mould remover, in a green bottle, wipe off after 5 mins. Once a year, about late January, does it for me

Its really not a big deal.
 
Well unfortunately I can call myself something of an expert on black mould, though not in connection with underfloor heating.

"Astonish" mould remover, in a green bottle, wipe off after 5 mins. Once a year, about late January, does it for me

Its really not a big deal.

You have underfloor heating with wood floors? how do you find the heat up times? any noticeable difference with tiled room?
 
That is interesting JohnJay, as builder told us since its a new houes, a3 rating, it's super warm and that will cause black mold to form quicker than seen in older houses.

Mold grows in spots where condensation forms. Condensation forms as a result of warm moisture laden air coming in contact with a colder surface. If your house is super warm, you won't have too many cold surfaces! If your ventilation is up to scratch, you should be able to keep humidity under control. I'd be worried about a builder giving you that kind of information now.

I have found a lot of material online about it... but i don't know who to trust.
I go on to one website and it states you can't use hardwood, the next says you can.

You can certainly use hardwood flooring with underfloor heating. It will act as an insulator as others have said, so it will cost you extra to run. You need to ensure your underfloor heating system can be set to run hotter in the rooms with underfloor heating to compensate. One example calculation from Junckers states that the underfloor heating needs to run at 37.5 degrees in order to achieve a surface temperature of 27 at the floor. See their technical guidance doc [broken link removed].

What is very important is the quality of the product used, and the skills and knowledge of those laying it. With the underfloor heating, there will be significantly more movement in your floor, so all joints will need to accommodate this movement, and you need to be happy that there will be small gaps between boards as they contract.

Engineered hardwood flooring will be a lot more stable.

One independent (seemingly) said that wood could be used but had to be very cautious to prevent moisture damage. i.e. let the subfloor and wood acclimatise over a few weeks.

Again, any product suitable for use will have guidelines such as the Junckers one above that will state what levels the relative humidity of the building and the flooring need to be at before installation. If the shop can't give you a copy of those, go elsewhere.

You will need to leave the new floors, and the rest of the build to dry completely, again ensuring the RH values are at or below the manufacturers guidelines, this can take weeks or longer in a new house. Then the flooring will need to acclimatise for a time in the room in which it is to be laid. After installation, you will not be able to use the underfloor heating for 2+ weeks, and then it will need to be introduced gradually over a week or so before hitting full temperatures. If the prep isn't done right, you'll end up with a mess that will only be suitable for a skip. So perhaps consider a temporary floor if you can't comfortably hit the humidity levels now and go without heating as required.
 
Not sure if its any use but i seen a test before where someone stuck down a large square of see through plastic to the ground for a few days and seen if water formed underneath it. This was to test if the room would be suitable for wooden floors.

Apparently it takes 60 days for the moisture to leave the concrete ground so should only be done after that.
 
Not sure if its any use but i seen a test before where someone stuck down a large square of see through plastic to the ground for a few days and seen if water formed underneath it. This was to test if the room would be suitable for wooden floors.

That's a handy DIY job, but any decent installer will have a meter that will accurately measure the moisture content.
 
That builder is talking nonsense. I've had engineered wood floors on top of underfloor heating for more than a decade and have never seen a hint of any mould. Where does he think the moisture to promote mould is supposed to come from?

I agree that you want your floor to acclimatise gradually after installation. However, I totally disagree with a couple of statements made up thread to the effect that "wood is an insulator so your system will be more expensive to run" and "you'll have to set the temperature higher to compensate". Where does one imagine the supposed additional energy goes (assuming one believes in the conservation of energy, the most basic of physical principles)?

What actually happens is that you get a steeper temperature gradient through an insulator. You can easily feel this with UFH wherever you have, say, a mat on the floor. Move the mat and you will feel that the temperature underneath is considerably higher. It's the same water at the same temperature as the rest of the room that is producing that. Remember, it's your thermostat that sets the temperature in the room, so the temperature gradient through your floor covering has to compensate to produce the same room temperature. The temperature gradient just sets the rate of energy release to compensate for the floor covering -- it can't possibly take more energy to heat the same room to the same temperature (unless either the floor covering itself has significant thermal mass, which it doesn't, or your subfloor insulation is deficient).

The warm-up time for wood compared to, say, tiles, is a little longer in order to establish the temperature gradient... but the warm-up time for UFH is abysmal anyway and you should not be using it in the first place if you expect to regularly need instant heat starting from cold.
 
However, I totally disagree with a couple of statements made up thread to the effect that "wood is an insulator so your system will be more expensive to run" and "you'll have to set the temperature higher to compensate". Where does one imagine the supposed additional energy goes (assuming one believes in the conservation of energy, the most basic of physical principles)?

Did you go through the Junckers calculations? It's certainly not in their interest to make those claims. The temperature mentioned relates to the temperature of the water in the heating system, not the stat temperatures.
 
Did you go through the Junckers calculations? It's certainly not in their interest to make those claims. The temperature mentioned relates to the temperature of the water in the heating system, not the stat temperatures.
Yes, I took a look. All it tells me is that you will get a higher temperature gradient through a more insulating material. That's what I'd expect. Their example uses a fixed energy flux of 70 W/m². That's the definition of your energy usage. The fact that you need a higher temperature gradient to achieve it has no bearing on the energy usage. All it means is that the water flowing through the pipes will lose less energy for a given temperature than a less insulating material -- that's the definition of insulation and is why you need the higher gradient. 70 W/m² is the same energy output regardless.
 
But you'll also get a higher portion of losses trough the system unless insullation levels are increased, so it will cost more to run, and it will be less responsive, but the latter generally isn't an issue if the house as a whole has a high standard of insulation. There'll be further complications if there are differing flooring materials, especially within a single zone.
 
Solution: get a dehumidifier or open the vents in each room to create circulation. Clean the black mould off the skirtings then spray with mould killer. Black mould on skirtings is common in areas upheated especially if the area is not well circulated with air.
 
But you'll also get a higher portion of losses trough the system unless insullation levels are increased, so it will cost more to run, and it will be less responsive, but the latter generally isn't an issue if the house as a whole has a high standard of insulation. There'll be further complications if there are differing flooring materials, especially within a single zone.
This is the bit I don't understand. How do you figure that? Those Junckers calculations aim for a given temperature at the floor surface. Assuming adequate underfloor insulation (without which UFH wouldn't work at all) the heat losses in your room (through walls, windows etc., being measured in W/m²/K) only depend on that surface temperature. Differing floor materials in different zones make no difference. The thermostatic controls simply ensure that a zone with a more conductive floor material cuts out quicker, giving the same floor surface temperature and same energy flux. As I've said, I've been using UFH for more than a decade, with a mixture of wood and tiled floors, and the temperature stability in all zones is to within a very impressive couple of tenths of a degree.
 
No insulation is 100% effective, with thermally efficient floor coverings, you will only have small losses via through the sub-floor insulation as the heat generated passes easily through the floor into the room. The higher the insulation value of the floor covering, the higher the percentage of heat energy will be lost through the sub-floor insulation into the ground.

To deliver a set amount of heat energy into the room, the slab will have to be heated to a higher temperature. Initially, this will result in a higher energy use to get it up to temperature, how much more energy this will consume over time will depend on the rate at which this built-up heat energy is being lost at and how often and for how long the heating is running.

If you have very deep/ effective insulation under the floor and very careful attention was given to eliminating thermal bridges during the construction, then losses will be minimised, but you will still have losses.
 
No insulation is 100% effective, with thermally efficient floor coverings, you will only have small losses via through the sub-floor insulation as the heat generated passes easily through the floor into the room. The higher the insulation value of the floor covering, the higher the percentage of heat energy will be lost through the sub-floor insulation into the ground.

To deliver a set amount of heat energy into the room, the slab will have to be heated to a higher temperature. Initially, this will result in a higher energy use to get it up to temperature, how much more energy this will consume over time will depend on the rate at which this built-up heat energy is being lost at and how often and for how long the heating is running.

If you have very deep/ effective insulation under the floor and very careful attention was given to eliminating thermal bridges during the construction, then losses will be minimised, but you will still have losses.
Note that additional energy to get the floor to temperature is not "wasted" as this will all come out through the floor surface (including during the matching longer cool-down times), minus any additional sub-floor losses. The rest is undoubtedly true, but it is worth calculating a realistic magnitude of the losses. The Junckers examples linked earlier gave a temperature difference (ΔT) of 4 degrees to overcome the thermal resistance of 14mm boards (similar to what I have) at a normal 50 W/m² output. That rises to 9 degrees with 22mm boards at 70 W/m². As you say, real world effectiveness of underfloor insulation depends on factors like thermal bridging but these can be taken into account (assuming a quality installation) by considering the ratio of floor area to perimeter length. Here are tables for various ratios and thicknesses of Kingspan TF70 insulation: http://www.kingspaninsulation.ie/getattachment/5fdd04b2-e58e-4622-97bb-5861799ab02a/Therma-TF70.aspx and for "Kore Floor": [broken link removed]

Insulation values of 0.2 W/m²K are easily achievable and 0.1 W/m²K is possible. Taking the Junckers figures ranging from ΔT=4K at 50 W/m² to ΔT=9K at 70 W/m², this gives losses ranging from 0.8% to 2.6% compared to a floor covering with zero thermal resistance. Since even porcelain tiles don't have zero resistance, I'd expect the actual differences in running costs to be less than 1% in the real world. That's negligible, especially compared to the real cost factors such as making sure that heating times are synched to your actual needs and not heating zones unnecessarily.
 
The additional energy used to get the slab up to temperature is wasted unless the cool-down time is so long as to maintain the temperature above what it naturally falls back to before the heating is switched on again.

As you say, a quality installation (of both sub-floor insulation and of all piping runs) minimises losses, but it still stands that it will cost more over time and be less reactive, and anyone considering such flooring should be aware of that.
 
The additional energy used to get the slab up to temperature is wasted unless the cool-down time is so long as to maintain the temperature above what it naturally falls back to before the heating is switched on again.
Apart from subfloor losses (which are negligible) that has to happen. Where would the energy go otherwise?
 
It's lost through the insulation, it's impossible to achieve zero losses.
 
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