UFH laid between joists - a matter of weight.

[Pet]

Hi All, I queried the matter of UFH in an up-stairs floor a few months ago and was given lots of advice Thanks. The next dilema I have, is, I have been advised the most effective/efficient method is by battons then 9mm ply and a biscuit screed (?) on and around the pipes. (with an insulation layer in there somewhere)

Advice on the following would be great. batton size and height from top of joists, what type of insulation (and where it goes in the "sandwitch" and, the main thing of concern... weight loading on joists, is there any reason the joist of a 70's built house would not be able to withstand the increased loading of the weight of the new screed floor? Maximum joist span is no greater than 4.5M

Oh, also.... is there any rough guide as to quantity of sand/cement required. e.g. if screed is 60cm thick (if that's the right thickness) what quantities of sand / cement would be required to cover what area.

Sorry if I'm being a bit vague.

Cheers

[Peter Parry]

Our UF heating is simply clipped into shaped aluminium plates which act as heat spreaders. The plates are screwed to the joists and the flooring laid on top. Works fine and a lot simpler than the method you seem to be contemplating.

Screed is usually used for the ground floor, I've not seen it recommended for a wooden first floor (although it is used if you have all concrete floors).

[rob w]

We have underfloor heating and its just screwed straight to the chipboard flooring every 300mm ( thousands of bloody clips, we had to take the nail out drill the clip and use a screww )then 1" foam insulation under this. It works great very pleased indead.

[David Moodie]

As this is upstairs, and between the joists I hope that the screed is 60mm rather than cm :-) But that aside, some of the best and most reliable info can be obtained from the manufactures and installers. I've been looking at UFH for the extension that I'm currently designing and received some decent design info, including eth sort that you are after from

are based up on Ullapool in the NW of Scotland but there client list extends all over the UK so don't let that put you off at least filling in there estimate form and getting a quote and design from them... this is beginning to sound like I work for them :-)... (insert usual disclaimers, no connection etc etc)

A few other ideas for the installation with reference to the batten size and construction which may be of use to you can be found at

David

[N. Thornton]

I cant say I'd recommend putting 2' thick screed on a first floor :) Or any screed for that matter, it doesnt make sense.

Regards, NT

[Christian McArdle]

You've got the wrong system. There is no need for screed in upstairs underfloor heating. Investigate underfloor heating designed specifically for suspended wooden floors.

You can get panels filled with plastic pipe and spreaders that attach between the joists. A bit of insulation underneath, coupled with boarding above is all you need, with no substantial raising of floor level, either.

Heat output is limited on wooden underfloor heating to prevent warping of the joists and boards. If you have inadequete wall or ceiling insulation, or substantially glazed areas, you may need additional heating in the room, although this can be only a fraction of the size needed compared to not having the underfloor. You need to do the calcs to be sure.

Christian.

[Pet]

I have got a quote from Nu-heat but their quote is based on either the screeed around pipes as detailed on the above page, or, using their chanelled foam with spreader plates which pushes the price up by nearly £700 also... on the invisible-heating site (I think) it states the screed (backfill) is also more beneficial from a soundproofing aspect which is a very high on our importance list as upstairs is the living area and bedrooms are downstairs.

Though the following paragraph -

" The infill is not Intended as load bearing merely as a heat transferance medium. CONSULT YOUR ARCHITECT OR STRUCTURAL ENGINEER TO ASSESS FLOOR SUITABILITY"

Makes me wonder if anyone knows of a "structural engineer" that could advise acordingly.

Cheers Pete

[Christian McArdle]

Should you have problems with floor weight, you may have to consider losing the screed. There are many suitable systems, such as

have no experience with the actual system, so can't tell you if it is recommended. However, I bet it will have a lot less weight. You basically lift the floorboards, insulate the joists, lay spreader plates over the joists, stick plastic pipe into the grooves in the plates (the pipework lies below the top of the joist and stick the floorboards back down. The floor height is raised by the thickness of a sheet of metal plate.

If you really want the extra sound proofing and do have enough weight capacity in the roof (possibly unlikely, as the joist will often have been carefully selected as the thinnest allowed), pour sand between the joists below the insulation. You still get the advantage of having almost no increased floor height.

The system above doesn't require channeled foam. AFAICT, you can use standard foam or rockwool insulation as the spreader plates support the pipework.

Christian.

[Pet]

Looks like a minimum of 25mm is fine

's to increase "thermal mass" like a storage heater I s'pose.

[The Natural Philosopher]

Actually, you can get away with pipes simply laid beteen the joists over a bed of rockwool, or celotex.

Not top banana for heat transfer, but good enough.

You are aiming for a warm floor, and a much cooler ceiling below.

Convection around the pipes will carry heat to the wood above almost as efficiently as screed.

Naturally people who sell expensive bits to do somewhat better will not tell you this.

:-)

[Peter Parry]

I really can't see why you would want to do this on a first floor - it's complicated and much simpler heat spreaders would work just as well. There is no need to make a storage heater.

[N. Thornton]

IMHO its not fine at all. Someone somewhere just isnt understanding the subject.

Regards, NT

[IMM]

Huf Haus have a screen on a suspended wooden floor.

[IMM]

Put high density Rockwool slbs between in the floor space. 75% fill.

[The Natural Philosopher]

We were discussing screeds, not screens.

>

[David Moodie]

Hi Pete

I was just researching some plastic pipe options for my central heating / water and came up with another link/option which I don't think has been mentioned Have a look at the UFH section at

looks to be a neat but expensive option for bewteen joist application. It appears that they have a combined insulation spreader plate solution that would offer reduced weight for your first floor application. Fill in there literature request and tehy will supply the literature , including prices to give you a rough idea. I only contacted them yesterday afternoon and teh info popped through the door this morning,

The only issue with the Wavin advice that I've come across so far that seems a bit suspect is the quote below " The final floor deck can be 20-25mm softwood or hardwood planks. Alternatively it can be 18-22mm chipboard or ply, covered in a timber finish or underlay and carpet. " I've not come across any other supplier who actullay recommends underlay and carpet, as this would generally provide too much insulation.

cheers

David

[Christian McArdle]

You'd have to derate the output. However, in a well insulated house, this might not be a problem, or a small radiator might be enough to make up the difference.

It's not a case of recommending underlay and carpet, it's just a case of recognising that this is what some people want.

Christian.

[Pet]

Thanks David, Greatly appreciated. Re: Underlay/carpet, the Chip-board panells with integral 10mm pipe is an interesting solution, though not one that would suit my needs. However they state "Due to the higher achievable outputs from these products they suit high resistance floor coverings such as underlay and carpet."

Nu-heat also say carpets/underlay _can_ be used, but should be allowed for on planning closer spacing and higher output is required. (I think that's where I saw it)

Cheers Pete