Undertile insulation

josip

We're insulating an existing house before we move in. The only weak spot left are the kitchen tiles on the concrete floor and I had thought to put tilebacker boards under them, the type that are used under electrical underfloor heating system. I've been quoted 53 Euro/sqm inc VAT however for a 10mm sheet of the best known brand on the Irish market. That's more than we're paying for the tiles! Can I get away with putting 12mm of ply under them instead?

Buford T Justice

Why can't you tile directly to the concrete?

Antiquo

IMO waste of money going for tilebacker if you're not going for the heating mat. Wouldn't bother with the ply it will be a bitch to fix to concrete. A tile on ply/insulation is as cold to walk on as the tile laid on concrete. If you really want a warm tile go for the elec heating option.

Merch

Antiquo wrote: »

IMO waste of money going for tilebacker if you're not going for the heating mat. Wouldn't bother with the ply it will be a bitch to fix to concrete. A tile on ply/insulation is as cold to walk on as the tile laid on concrete. If you really want a warm tile go for the elec heating option.

But surely unless you insulate under that the majority of heat will be lost through the floor to outside?
Also elec isnt the cheapest way/rate to heat anyway.

Antiquo

Merch wrote: »

But surely unless you insulate under that the majority of heat will be lost through the floor to outside?
Also elec isnt the cheapest way/rate to heat anyway.

Heat rises and I'm assuming the floor is already insulated. As for the elec mat is only on for a couple of hours in the early morning and late aftenoon to take chill out of tiles and acts as storage heater for some time after turning off.

Merch

Antiquo wrote: »

Heat rises and I'm assuming the floor is already insulated. As for the elec mat is only on for a couple of hours in the early morning and late aftenoon to take chill out of tiles and acts as storage heater for some time after turning off.

Yes, heat rises in air, due to convection, but under the floor that heat will also be transmitted by conduction to the colder surfaces below it. Assuming its insulated some of that loss will be negated and further so if it only switched on briefly. But if its not insulated then I'd guess it would soak heat away?? thats how I'd see it? but Im not an expert.

josip

Merch and Antiquo, thanks for the replies and you've identified my 2 issues with the floor tiles. One is that they will be a source of heat loss from an otherwise well insulated house: A-windows, drylined, airtightened, HRV. The rest of the downstairs floor will be solid wood which will insulate well. The second issue is that they will feel cold to walk on unless I have something with decent soles.

As regards how much heat would be lost, that's debatable. The surface area is quite small. Heat does rise, and going back to my Young Scientist days the difference in temp between the ceiling and floor in a room is on average 6C. Which is why I would have liked UFH, but retrofitting it into a 30 year old house would have been too much. Would a 30 year old semi-d have any insulation in the floor btw? Anyway back to the heat loss issue. Assuming that the room is a solid envelope, the initial loss of heat from a room must take place via conduction. What determines how much heat will be lost, will be the temperature gradient on either side of the material and the thermal conductivity of the material. Here are some thermal conductivity values

http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html

The ones that concern us are the concrete (1.7), porcelain (1.5) and polyurethane (0.02)(drylining boards). I won't go into any formulas that I myself haven't understood for 20 years but these numbers show that even with a smaller temp gradient between the flor and the ground than the walls and the outside air, the stone floor sucks heat out at a terrifying rate.

But even if I do put in a plywood layer, I think the tiles will still feel cold unless they are heated for the same reasons I've just outlined. But the difference in price between a few sheets of ply and the CAPEX and OPEX of electrical UFH would pay for slippers for life for my whole family.

Ramble over

antoinolachtnai

Half an inch of plywood isn't going to provide much or any insulation.

I would be concerned about ventilating the plywood too. If it's not ventilated, and it gets even slightly wet (from damp rising from under the subfloor if there is any fault with the dampproofing, or from even a small leak in the kitchen, or from condensation, it will rot.

It's really a matter of comfort rather than expecting insulation that will return value based on today's energy prices. In general that is the situation for any insulation retrofit, especially windows, for example. The purpose of the backer board isn't so much to insulate the building as to accelerate the rate at which the UFH heats up and cools down.

If I were you, I would just put down underfloor heating for the circulation areas. If you need it for comfort, you can use it. If you don't want to use it, you don't have to.

For example:

http://www.underfloorheatingmats.co.uk/category/economy-floor-heat---matting-system---200-w

Keeping the chill off the floor can reduce the amount of space heating you require, so it isn't all a loss. If you can run it at night, on a night rate, it's not an awful lot more expensive than gas.

Joey the lips

In all my experience i have never seen any tile on concrete floor being insulated enough. If you run heat mats its un economical. Heat matts are not efficent and only advised over short distance. If you ply back the floor the tile will still hold and retain the cold. The only reason it does not upstairs is because of the riseing heat element.

If you want a warm floor in tile buy marble. It will be a lot less colder but will still be cold. It breaths however in a kitchen and hall you need to seal it so it wont breath.

If you want a warm floor buy wood. Its cheaper to replace and the replacement cost will still be less than the wasted electricity on the matts.

heinbloed

@Josip:

How much space is there available for insulation?

Carlow52

Conductivity is all very well but it ignores thickness of the material in question
so

http://www.engineeringtoolbox.com/heat-loss-transmission-d_748.html

shows the effect of thickness via the R value

personally I would go with some floor mats and tile onto the concrete

IMO 1/2" ply is a waste of time and effort

I would have a standard towel rad and a wall mounted elec fan heater, the rad to maintain temp at 16 or so and the fan to bring it up to what ever is required, it also doubles as a hair drier

josip

heinbloed wrote: »

@Josip:

How much space is there available for insulation?

Hi Heinbloed,

The parquet block in the living room that the kitchen tiles will be adjoining is 22mm thick. The tiles are 10mm. I'd rather have a minimal step up or down so I think 10 to 12mm.

heinbloed

Well, with 10mm space the effort of putting insulation down isn't worth it.
There is 10mm strong insulation available, on rolls (EPS), more packaging material than structural material.
But the loadbearing quality is rather poor.
What you still could do is to place a good quality water/vapour barrier there.

A standard UFH would be in such a situation a no-go, at least if you have to pay for the fuel. An alternative could be a micro bore (8-10 mm) UFH fed with solar thermal energy, a low thermal harvest can be expected on any winter's day.
Contrary to what many ST installers say.
The disadvantage of the micro-bore systems is their tendency to sludge-up as previous posters have said already. Install a sludge trap to overcome this, install an easy access flushing valve in case it happens despite the sludge trap.
Such an installation wouldn't be cheap (price per available/harvested kWh), if it is worth it depends on on the alternatives.

If you plan for a ST system anyhow install a seperate storage tank only for the UFH, this would avoid the mixing of the low temperature ST winter harvest with the central heating energy. A mixing that would cost to much of the paid fuel.

Another (fuel cost demanding !) alternative would be again the micro bore system running on a very low temperature, achieved with a mixing valve. The idea is to raise the natural floor temperature by only 1-4 degrees and covering the bulk of space heating demand as usual with wet radiators or whatever.
The UFH would be there for more comfort, not because it would be an economical way of heating the room.

Contact an energy advisor or heating engineer for a calculated design.

Good luck!

Antiquo

Carlow52 wrote: »

I would have a standard towel rad and a wall mounted elec fan heater, the rad to maintain temp at 16 or so and the fan to bring it up to what ever is required, it also doubles as a hair drier

Just trying to get a vision of what you get up to in your kitchen:D

josip

heinbloed wrote: »

Well, with 10mm space the effort of putting insulation down isn't worth it.

...
A standard UFH would be in such a situation a no-go, at least if you have to pay for the fuel. An alternative could be a micro bore (8-10 mm) UFH fed with solar thermal energy, a low thermal harvest can be expected on any winter's day.
Contrary to what many ST installers say.
The disadvantage of the micro-bore systems is their tendency to sludge-up as previous posters have said already. Install a sludge trap to overcome this, install an easy access flushing valve in case it happens despite the sludge trap.
Such an installation wouldn't be cheap (price per available/harvested kWh), if it is worth it depends on on the alternatives.

If you plan for a ST system anyhow install a seperate storage tank only for the UFH, this would avoid the mixing of the low temperature ST winter harvest with the central heating energy. A mixing that would cost to much of the paid fuel.

...

Good luck!

Thanks Heinbloed,

We've just had a ST system installed but with a solar cylinder where the bottom half is the thermal store and the upper half is coheated by Gas boiler. I'll check if there's an outlet from the cylinder at the halfway point that can be used and will enquire about the microbore if there is.

Josip.