Would appreciate input on the spacing between the pipes on an underfloor heating system, starting a self build bungalow going to go with air sourced heat pump, trying to work out heating requirements. Seems to be conflicting advice on how close the pipes should be to each other. Pipe diameter also a factorbut what is the experience from people here?

Any experience on using the tray type system versus the staple to the floor system?

Also how would the floor structure be made up have been told - 100mm hardcore, blinding sand, DPM, then insulation boards then concrete then UFH pipes then screed? But doesn't this mean that you are heating up a a slab of concrete? Have to use trays this way.

Make more sense to go 100mm hardcore, blinding sand the DPM, then concrete then insulation boards, then UFH pipes then screed. This way i can staple the pipe to the boards.

Any views on an eco insulation board rather than the poly urethane boards, have used sheeps wool insulation and hemp insulation from Black Mountain before on lofts and walls which were great but they don't do a board and they couldn't recommend one.

Welcome everyones thoughts.

o.028 U value from memory.

Can't you work it out from the conductance of the plate material and the heat losses though the floor and to the air (where you want the heat). You will also need to know the power that the pipe can deliver, so that will be the pipe thermal properties and the flow rate for any given temperature. Do the manufacturers of the system not have tables?

''Any views on an eco insulation board rather than the poly urethane boards, have used sheeps wool insulation and hemp insulation from Black Mountain before on lofts and walls which were great but they don't do a board and they couldn't recommend one.''

At South Yorkshire Energy Centre we used NBT's wood-fibre boards. Seems to be OK, but bear in mind that, compared to Pu, you'd need nearly twice the thickness, and it's pricey.

Yes, if it's really 0.28 W/m²·K for a new build then it's close to off-topic for this forum unless there's a weird special reason. Should be trying to do better than half that conduction for the UK. If you're in a climate where that level of insulation is not justified then UFH is probably a waste, anyway.

Second Nick's comment on wood-fibre board. Can't staple to it, and AFA heat loss goes, sometimes it just has to be foam. That's what the Bubble-bath rep said, anyway.....

Ed: Coupla points: Not all builds are 'new' as in the PP is years old and the U-values at the time were great if they were anything below 1!!! Off-topic....my Dutch cap....you sound like a green headmaster!! Stop nit-picking and let the man fit his UFH. If you feel you have to crusade, do so by campaigning for EWI/IWI on by far the main domestic wastage in the UK - existing housing stock, not a guy who's asking advice - from this forum - to do the best he can within his green agenda and pricing structure. Or you could always try campaigning in interior China, where, allegedly, the U values are approaching 3.0 and counting....get it in perspective along with the ideological missionary zeal pleeeease.

2nd point: UFH a waste in low-insulation dwellings? Come off it. The lower flow temps allowed either keep a condensing boiler firmly in its C spot, or allow better COPs from a heat-pump. Either way, widely-agreed savings are IRO 20% against 'traditional systems. So waste it ain't. And of course, our enquirer could always upgrade the insulation hereafter, perhaps at the same rate as the Chinese...

CDs: Maybe I am now nit-picking but allowing greater pipe density in the floor does not achieve a low flow temperature. It certainly enables it - and gives you flexibility of suply - via suitable controls.

David of the middle 1st Legion: Talk to your supplier. 14, 15 and 16mm are all common on systems I have fitted recently. With the right Euro-cones and spacing, diameter is relatively irrelevant. Typical stratification is: Oversite concrete, DPM, insulation, pipe-in-screed. Although creative methods such as the kiln-burnt/clay tiles with moulded channel (Back to earth I believe, Exeter) are becoming common.

Very limited benefit insulating underneath the oversite as you have to insulate beneath the screed and pipe anyway, and you may as well add more under the screed. Low screed density (thickness) makes for more controllability. And forget trays unless you are on a first (suspended) floor. Use bifular rather than linear pattern. More on this in a thread I started a while ago. Search on More Efficient UFH.

Edit: Spacings, aka density, 150mm is way plenty, 'even' at .28 U value.

Posted By: crusoeEd: Coupla points: Not all builds are 'new' as in the PP is years old and the U-values at the time were great if they were anything below 1!!!

What's the date of the planning permission got to do with the matter?

Posted By: crusoe2nd point: UFH a waste in low-insulation dwellings? Come off it.

That is not at all what I said. I quite clearly stated that I was talking about a climate where higher levels of insulation are not justified and from the context it's obvious I'm talking about a new build. Of course retrofit is difficult so lower levels of insulation on older buildings have to be accepted. If you have an existing building which requires a reasonable amount of heating then I think UFH is great. I just question the wisdom of building something new which needs sufficient heating that UFH makes sense in our current energy situation.

Borpin , reinforcing fabric mesh A98 or A142
My prefered build up , HC, blinding, DPM, 200mm EPS,DPM,100-150mm concrete slab with UFH pipes tied to top of A98 mesh lifted up off EPS/DPM 25-50mm ish on mesh feet, trowel to finish, level tex if I'm a bit off on my finish.

Posted By: TimSmall

Posted By: borpin
I'm doing blinding, DPM, 150mm PIR insulation (plus edge ins)

PIR is a little bit iffy under floor isn't it? Needs to be fully wrapped in a carefully joined, heavy duty DPM, otherwise may become waterlogged at the bottom edge in the very long term (and even then, still might in very long term)?

DPM needs to be well done as you say - not sure I'd use the term iffy but I'll let you know in 20 years how it has worked.....

yes , light weight as in not structual slab mesh, only 5-6mm bars ,200mm spacing
works well , though a little fiddly walking about on the mesh cable tieing the pipe with big boots on , best to find someone with small feet to do the job.

15mm speedfit polybutlene , 100-120m lengths , 100mm ish spacing , approx 12m2 per 100m coil (120m coils leaves some to return to manifold on larger jobs)
Like speedfit as it's manifactured local to me , used other brands occasionally
good info from polypipe here, wouldn't bother with there red eggbox pipes laying template though
http://download.polypipe.com/bp/brochures/tig1_under_floor_tech_install.pdf

Just got home from working away, the U value was 0.18 not 0.28. Makes more sense regarding the comments. Thanks for everyones input really appreciate it. Like the idea of using mesh. The kitchen, diner, family room is 65m2 which is a lot of pipe at 100mm spacing. Looks like it is PIR board for insulation, Evens at Black Mountain returned my call today and even he said it was the route he would suggest! Gave me the name of a retailer that was running a summer price promotion on natural insulations, will check them out tomorrow.
Really good input thanks.

Posted By: borpin[PIR under floor] DPM needs to be well done as you say - not sure I'd use the term iffy but I'll let you know in 20 years how it has worked.....

I suppose what I'm saying, is why not use EPS100 instead of the PIR? It's got a far longer track record under screed, doesn't have problems with pentane-loss over time leading to reduced insulation performance (perhaps this is less of a problem if you wrap it in a radon barrier grade DPM?), but perhaps most importantly, it doesn't lose so much of its insulation value when damp. It's cheaper and I believe takes a bit less energy to manufacture than PIR. As it doesn't have foil facing, you can also use two layer and glue them together with a PU foam glue like Soudatherm Roof 250 to create a very solid raft for your slab (which you could probably make a bit thinner as a result).

What's not to like?

BTW, I've seen a PU warm deck roof come off absolutely saturated - I'd estimate the boards were 5 times heavier than they were originally, due to the water they were holding. This was (I believe) due to a roof leak, but some WUFI simulations of PIR over extended time periods (decades) have show moisture build up in the PIR too. Better foil-tape the PIR too just in case...

Posted By: TimSmallWhat's not to like?

The insulation value. If I had the depth/height I probably would but with what I have available I need the higher value for the a relatively small depth.

The insulation takes quite a bashing when you lay the screed , this should flatten out the board if there's a bit of a bend.
I think it depends on various things though. Thickness of screed , thickness of board.
If trad. screed then 75mm seems a minimum thickness with UFH pipes , if you floors ins. a thick build up better to have 2 boards rather than 1 to allow them to flatten out easier, eg if EPS 2 x 100mm. PUR 2 x 60mm etc.
Trad. screed goes down pretty dry to reduce shrinkage, settlement. I'd have thought you dont really want any settlement at all as this may crack the screed.
My kitchen floor was done using the build up I mentioned above and it rings , I think this may be more to do with 125mm concrete sitting on 200mm EPS creating some kind of acoustic vibration ?
Off to do a 18m2 trad. screed with UFH now , what fun